# AC 00-45F CHG 2: Aviation Weather Services - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Historical - Approved: March 12, 2009 - Last reviewed: September 13, 2024 - This change: This entire document series, all through the H Revision, is canceled. - Family: AC 00-45 - Cancels: [AC 00-45F CHG 1](https://openairdocs.org/ac/00-45F-CHG-1) - Cancelled by: [AC 00-45F CHG 2](https://openairdocs.org/ac/00-45F-CHG-2) - 14 CFR parts: 1 - Pages: 388 - PDF: https://openairdocs.org/files/sha256/ce/9a/ce9ab669ad214fcab4bb23371ddb8d97e34b46b31ca1fca1d39804ec4f982aff - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID173748422020240913191641.0001 - DRS record last changed: November 21, 2025 - Page: https://openairdocs.org/ac/00-45F-CHG-2 ## Versions - [AC 00-45H CHG 2](https://openairdocs.org/ac/00-45) (Historical), approved Mar 6, 2019, 348 pages. CHG 2 of AC 00-45H. This entire document series, all through the H Revision, is canceled. - [AC 00-45H CHG 1](https://openairdocs.org/ac/00-45H-CHG-1) (Historical), approved Jan 8, 2018, 346 pages. CHG 1 of AC 00-45H. This entire document series, all through the H Revision, is canceled. - [AC 00-45H](https://openairdocs.org/ac/00-45H) (Historical), approved Nov 14, 2016, 331 pages. This entire document series, all through the H Revision, is canceled. - [AC 00-45G CHG 2](https://openairdocs.org/ac/00-45G-CHG-2) (Historical), approved Oct 1, 2014, 427 pages. CHG 2 of AC 00-45G. This entire document series, all through the H Revision, is canceled. - [AC 00-45G CHG 1](https://openairdocs.org/ac/00-45G-CHG-1) (Historical), approved Jul 29, 2010, 405 pages. This entire document series, all through the H Revision, is canceled. - [AC 00-45G](https://openairdocs.org/ac/00-45G) (Historical), approved Feb 11, 2010, 1 page. This entire document series, all through the H Revision, is canceled. - [AC 00-45F CHG 2](https://openairdocs.org/ac/00-45F-CHG-2) (Historical), approved Mar 12, 2009, 388 pages. This entire document series, all through the H Revision, is canceled. - [AC 00-45F CHG 1](https://openairdocs.org/ac/00-45F-CHG-1) (Historical), approved Jul 1, 2008, 399 pages. This entire document series, all through the H Revision, is canceled. - [AC 00-45F](https://openairdocs.org/ac/00-45F) (Historical), approved Oct 1, 2007, 1 page. The AC 00-45F base document is unavailable. This entire document series, all through the H Revision, is canceled. - [AC 00-45E](https://openairdocs.org/ac/00-45E) (Historical), approved Dec 1, 1999, 211 pages. This entire document series, all through the H Revision, is canceled. ## Text Each page's text from the PDF; open the PDF at a page with #page=N. Some pages are OCR from the scanned FAA advisory circular. OCR can misread letters and numbers. Those pages are marked (OCR). ### Page 1 **AVIATION** **WEATHER** SERVICES Advisory Circular, AC 00-45F, Change 2 **U.S. DEPARTMENT OF COMMERCE** **NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION** **NATIONAL WEATHER SERVICE** **U.S. DEPARTMENT OF TRANSPORTATION** **FEDERAL AVIATION ADMINISTRATION** Photo courtesy of Aaron A. Gilstad Published March 12, 2009 ### Page 2 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Summary of Changes **SUMMARY OF CHANGES** SECTION CHANGE(S) Cover Specified that this is AC 00-45F, Change 2. The previous version of this document used the word “Revision” instead of “Change.” Did this to maintain consistency with other FAA Advisory Circulars. Also, changed NWS FAA Academy email address to: nws-faa.academy@noaa.gov Table of Contents Updated due to changes listed below. 1.3.7 Inserted ADS-B and FIS-B information. 3.1.4 Changed section title from “Examples of METAR Reports, Explanations, and Phraseology” to “METAR/SPECI Examples.” Replaced METAR/SPECI examples. 7.1 Updated FA product descriptions and replaced CONUS examples. 7.1.2 Inserted a note to define the terms “CSTL WTRS” and “CSTL SXNS” 7.1 Deleted “AND CSTL WTRS” from Figure 7-6 and Table 7-3. 7.2 Deleted TAF location maps. 7.2 Updated to 30-hour TAF format. 7.2.2 “Section 7.2.2.5 Valid period of Amended TAFs” was deleted and pertinent information was moved to section 7.2.2.4. 7.2.3 Sections 7.2.3.1 – 7.2.3.4 were updated to follow NWS Directive 10- 813 (dated 11/19/2007). 10, Appendix A Replaced “ASOS/AWOS Location Maps” with “Definitions of Common Terms used in En Route Forecasts and Advisories.” 15, Appendix F Updated Figure F-1. AWC Advisory Plotting Chart – Contiguous US and accompanying table. ### Page 3 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Foreword **FOREWORD** Aviation Weather Services, Advisory Circular 00-45F, is published jointly by the National Weather Service (NWS) and the Federal Aviation Administration (FAA). This publication supplements its companion manual Aviation Weather, Advisory Circular 00-6A, which documents weather theory and its application to the aviation community. This advisory circular, AC 00-45F, explains U.S. aviation weather products and services. It details the interpretation and application of advisories, coded weather reports, forecasts, observed and prognostic weather charts, and radar and satellite imagery. Product examples and explanations are taken primarily from the Aviation Weather Center’s Aviation Digital Data Service website (http://adds.aviationweather.noaa.gov/). The AC 00-45F was written by Robert A. Prentice with assistance from Douglas D. Streu, and edited by Cynthia Abelman and Tom Dulong. Stan Roberts (AFS-600) was the reviewer for the FAA. Additional contributors include Raymond Tanabe, Larry Burch, Duane Carpenter, Lisa Glikbarg, Celia Miner, Ronald Olson, Richard Akers, Bill Carle, and Christa Jacobs. An online version of this document can be found at: http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/MainFram e?OpenFrameSet or http://www.srh.noaa.gov/faa/pubs.html Comments and suggestions for improving this publication are encouraged and should be directed to: E-mail nws-faa.academy@noaa.gov US Postal Mail NATIONAL WEATHER SERVICE, W/SR64 BLDG 30, RM 107 6500 S MACARTHUR BLVD OKLAHOMA CITY OK 73169-6901 Aviation Weather Services, Advisory Circular, AC 00-45F, Change 2, supersedes AC 00-45F, revision 1, published July 31, 2008. This AC document will be cancelled when the AC 00-45G is published on February 11, 2010. ### Page 4 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) NOTE: CLICK ON ANY ENTRY IN THE OF THE TABLE OF CONTENTS TO JUMP DIRECTLY TO THAT SECTION … XVI 1  AVIATION WEATHER SERVICE PROGRAM … 1-1 1.1  NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA) … 1-1 1.1.1  National Environmental Satellite Data and Information Service (NESDIS) … 1-1 1.1.1.1  Satellite Analysis Branch (SAB) … 1-1 1.1.2  National Weather Service (NWS) … 1-1 1.1.2.1  National Centers for Environmental Prediction (NCEP) … 1-1 1.1.2.1.1  NCEP Central Operations (NCO) … 1-2 1.1.2.1.2  Aviation Weather Center (AWC) … 1-2 1.1.2.1.3  Hydrometeorological Prediction Center (HPC) … 1-2 1.1.2.1.4  Storm Prediction Center (SPC) … 1-2 1.1.2.1.5  Tropical Prediction Center (TPC) … 1-2 1.1.2.2  Alaskan Aviation Weather Unit (AAWU) … 1-2 1.1.2.3  Center Weather Service Unit (CWSU) … 1-3 1.1.2.4  Weather Forecast Office (WFO) … 1-3 1.1.2.5  NWS Office at the FAA Academy … 1-3 1.2  FEDERAL AVIATION ADMINISTRATION (FAA) … 1-4 1.2.1  Air Traffic Control System Command Center (ATCSCC) … 1-4 1.2.2  Air Route Traffic Control Center (ARTCC) … 1-4 1.2.3  Air Traffic Control Tower (ATCT) and Terminal Radar Approach Control (TRACON) … 1-4 1.2.4  Flight Service Station (FSS) / Automated Flight Service Station (AFSS) … 1-5 1.3  DISSEMINATION OF AVIATION WEATHER PRODUCTS … 1-6 1.3.1  Weather Briefings … 1-6 1.3.1.1  Standard Briefing … 1-6 1.3.1.2  Abbreviated Briefing … 1-7 1.3.1.3  Outlook Briefing … 1-7 1.3.2  Direct Use Access Terminal Service (DUATS/DUAT) … 1-7 1.3.3  Aviation Digital Data Service (ADDS) … 1-8 1.3.4  Telephone Information Briefing Service (TIBS) … 1-8 1.3.5  Hazardous Inflight Weather Advisory Service (HIWAS) … 1-9 1.3.6  En Route Flight Advisory Service (EFAS) … 1-10 1.3.7  Automatic Dependent Surveillance – Broadcast (ADS-B) … 1-11 1.3.7.1  Flight Information Service – Broadcast (FIS-B) … 1-11 1.3.7.1.1  FIS-B Products … 1-11 1.3.7.1.2  Operational Use of FIS-B Products … 1-12 2  AVIATION WEATHER PRODUCT CLASSIFICATION AND POLICY … 2-1 2.1  CLASSIFICATION OF AVIATION WEATHER PRODUCTS … 2-1 2.1.1  Primary Weather Product Classification … 2-1 2.1.2  Supplementary Weather Product Classification … 2-1 2.2  TYPES OF AVIATION WEATHER INFORMATION … 2-2 2.2.1  Observations … 2-2 2.2.2  Analysis … 2-2 2.2.3  Forecasts … 2-2 2.3  CATEGORIZING AVIATION WEATHER SOURCES … 2-2 2.3.1  Federal Government … 2-2 2.3.2  Enhanced Weather Information System (EWINS) … 2-3 2.3.3  Commercial Weather Information Providers … 2-3 3  OBSERVED TEXT PRODUCTS … 3-1 **3.1 AVIATION ROUTINE WEATHER REPORTS (METAR) AND AVIATION SELECTED SPECIAL WEATHER** REPORTS (SPECI) … 3-1 3.1.1  Aviation Routine Weather Report (METAR) … 3-1 3.1.2  Aviation Selected Special Weather Report (SPECI) … 3-1 Table 3-1. SPECI Criteria … 3-2 AC 00-45F, CHG 2 Table of Contents Page i ### Page 5 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3  Format … 3-3 Figure 3-1. METAR/SPECI Coding Format … 3-3 3.1.3.1  Type of Report … 3-3 3.1.3.2  Station Identifier … 3-3 Figure 3-2. ICAO Continent codes … 3-4 3.1.3.3  Date and Time of Report … 3-5 3.1.3.4  Report Modifier (As Required) … 3-5 3.1.3.5  Wind Group … 3-6 3.1.3.5.1  Wind Gust … 3-6 3.1.3.5.2  Variable Wind Direction (speed 6 knots or less) … 3-6 3.1.3.5.3  Variable Wind Direction (speed greater than 6 knots) … 3-6 3.1.3.5.4  Calm Wind … 3-7 3.1.3.6  Visibility Group … 3-7 3.1.3.7  Runway Visual Range (RVR) Group … 3-7 3.1.3.8  Present Weather Group … 3-8 Table 3-2. METAR/SPECI Notations for Reporting Present Weather1 … 3-9 3.1.3.8.1  Intensity Qualifier … 3-10 3.1.3.8.2  Proximity Qualifier … 3-10 3.1.3.8.3  Descriptor Qualifier … 3-10 3.1.3.8.4  Precipitation … 3-11 3.1.3.8.5  Obscuration … 3-11 3.1.3.8.6  Other Weather Phenomena … 3-11 3.1.3.9  Sky Condition Group … 3-12 Figure 3-3. Obscuration Effects on Slant Range Visibility … 3-12 Table 3-3. METAR/SPECI Contractions for Sky Cover … 3-13 Table 3-4. METAR/SPECI Increments of Reportable Values of Sky Cover Height … 3-13 Figure 3-4. METAR/SPECI Sky Condition Coding … 3-14 3.1.3.10  Temperature/Dew Point Group … 3-15 3.1.3.11  Altimeter … 3-15 3.1.3.12  Remarks (RMK) … 3-15 Table 3-5. METAR/SPECI Order of Remarks … 3-16 3.1.3.13  Automated, Manual, and Plain Language Remarks … 3-17 3.1.3.13.1  Volcanic Eruptions (Plain Language) … 3-17 3.1.3.13.2  Funnel Cloud … 3-17 3.1.3.13.3  Type of Automated Station … 3-17 3.1.3.13.4  Peak Wind … 3-17 3.1.3.13.5  Wind Shift … 3-18 3.1.3.13.6  Tower or Surface Visibility … 3-18 3.1.3.13.7  Variable Prevailing Visibility … 3-18 3.1.3.13.8  Sector Visibility (Plain Language) … 3-18 3.1.3.13.9  Visibility at Second Location … 3-18 3.1.3.13.10 Lightning … 3-18 Table 3-6. METAR/SPECI Type and Frequency of Lightning … 3-19 3.1.3.13.11 Beginning and Ending of Precipitation … 3-19 3.1.3.13.12 Beginning and Ending of Thunderstorms … 3-19 3.1.3.13.13 Thunderstorm Location (Plain Language) … 3-19 3.1.3.13.14 Hailstone Size (Plain Language) … 3-19 3.1.3.13.15 Virga (Plain Language) … 3-20 3.1.3.13.16 Variable Ceiling Height … 3-20 3.1.3.13.17 Obscurations (Plain Language) … 3-20 3.1.3.13.18 Variable Sky Condition (Plain Language) … 3-20 3.1.3.13.19 Significant Cloud Types (Plain Language) … 3-20 3.1.3.13.19.1  Cumulonimbus or Cumulonimbus Mammatus … 3-20 Figure 3-5. Cumulonimbus (CB) Example … 3-21 Figure 3-6. Cumulonimbus Mammatus (CBMAM) Example … 3-21 3.1.3.13.19.2  Towering Cumulus … 3-22 Figure 3-7. Towering Cumulus (TCU) Example … 3-22 3.1.3.13.19.3  Altocumulus Castellanus … 3-23 Figure 3-8. Altocumulus Castellanus (ACC) Example … 3-23 3.1.3.13.19.4  Standing Lenticular or Rotor Clouds … 3-24 Figure 3-9. Standing Lenticular and Rotor Clouds Example … 3-24 3.1.3.13.20 Ceiling Height at Second Location … 3-24 AC 00-45F, CHG 2 Table of Contents Page ii ### Page 6 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.13.21 Pressure Rising or Falling Rapidly … 3-25 3.1.3.13.22 Sea-Level Pressure … 3-25 3.1.3.13.23 Aircraft Mishap (Plain Language) … 3-25 3.1.3.13.24 No SPECI Reports Taken (Plain Language) … 3-25 3.1.3.13.25 Snow Increasing Rapidly … 3-25 3.1.3.13.26 Other Significant Information (Plain Language) … 3-25 3.1.3.14  Additive and Automated Maintenance Data … 3-25 3.1.3.14.1  Hourly Temperature and Dew Point … 3-25 3.1.3.14.2  Maintenance Data Groups … 3-26 3.1.3.14.2.1  Sensor Status Indicators … 3-26 3.1.3.14.2.2  Maintenance Indicator … 3-26 3.1.4  METAR/SPECI Examples … 3-27 3.2  PILOT WEATHER REPORTS (PIREP) … 3-32 3.2.1  Format … 3-32 Figure 3-10. Pilot Weather Report (PIREP) Coding Format … 3-32 3.2.1.1  Message Type (UUA/UA) … 3-32 3.2.1.1.1  Urgent PIREPs … 3-32 3.2.1.1.2  Routine PIREPs … 3-33 3.2.1.2  Location (/OV) … 3-33 3.2.1.2.1  Location … 3-33 3.2.1.2.1.1  3.2.1.3.1.1 Route Segment … 3-33 3.2.1.3  Time (/TM) … 3-34 3.2.1.4  Altitude/Flight Level (/FL) … 3-34 3.2.1.5  Aircraft Type (/TP) … 3-34 3.2.1.6  Sky Condition (/SK) … 3-34 3.2.1.7  Flight Visibility and Weather (/WX) … 3-35 Table 3-7. PIREP Weather Type and Symbols … 3-36 3.2.1.8  Air Temperature (/TA) … 3-38 3.2.1.9  Wind Direction and Speed (/WV) … 3-38 3.2.1.10  Turbulence (/TB) … 3-38 Table 3-8. PIREP Turbulence Reporting Criteria … 3-39 3.2.1.11  Icing (/IC) … 3-39 Table 3-9. Icing Intensities, Contractions, and Airframe Ice Accumulation … 3-40 Table 3-10. Icing Types, Contractions, and Descriptions … 3-40 3.2.1.12  Remarks (/RM) … 3-40 3.2.1.12.1  Wind Shear … 3-41 3.2.1.12.2  FUNNEL CLOUD, TORNADO, and WATERSPOUT … 3-41 3.2.1.12.3  Thunderstorm … 3-41 3.2.1.12.4  Lightning … 3-41 3.2.1.12.5  Electrical Discharge … 3-41 3.2.1.12.6  Clouds … 3-42 3.2.1.12.7  Plain Language … 3-42 3.2.1.12.8  Volcanic Eruptions … 3-42 3.2.1.12.9  SKYSPOTTER … 3-42 3.2.2  PIREP Examples … 3-43 3.3  RADAR WEATHER REPORT (SD/ROB) … 3-45 Figure 3-11. Radar Weather Report (SD/ROB) Coding Format … 3-45 3.3.1  Format … 3-45 3.3.1.1  Location Identifier … 3-45 3.3.1.2  Time … 3-45 3.3.1.3  Configuration … 3-45 Figure 3-12. Radar Weather Report (SD/ROB) Configurations … 3-46 3.3.1.4  Coverage … 3-46 3.3.1.5  Precipitation Type … 3-46 3.3.1.6  Precipitation Intensity … 3-47 Table 3-11. SD/ROB Reportable Intensities … 3-47 3.3.1.7  Location … 3-47 Figure 3-13. SD/ROB AREA, Line (LN), and CELL Location Examples … 3-48 3.3.1.8  Maximum Top … 3-48 3.3.1.9  Cell Movement … 3-48 3.3.1.10  Remarks … 3-49 AC 00-45F, CHG 2 Table of Contents Page iii ### Page 7 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-12. Weather Radar Report Remarks and Meaning … 3-49 3.3.1.11  Digital Section … 3-49 Figure 3-14. SD/ROB Digital Section Information Plotted on a PPI Grid Overlay Example … 3-50 3.3.2  Examples … 3-50 Figure 3-15. WSR-88D Weather Radar Network Sites … 3-52 4  RADAR AND SATELLITE IMAGERY … 4-1 4.1  RADAR … 4-1 4.1.1  Description … 4-1 4.1.2  Modes of Operation … 4-1 4.1.2.1  Clear Air Mode … 4-1 4.1.2.2  Precipitation Mode … 4-1 4.1.3  Echo Intensities … 4-2 Figure 4-1. WSR-88D Weather Radar Echo Intensity Legend … 4-2 Table 4-1. WSR-88D Weather Radar Precipitation Intensity Terminology … 4-2 4.1.4  Products … 4-3 4.1.4.1  Base Reflectivity … 4-3 Figure 4-2. WSR-88D Weather Radar Short Range (124 NM) Base Reflectivity Product Example . … 4-3 Figure 4-3. WSR-88D Weather Radar Long Range (248 NM) Base Reflectivity Product Example 4- 4 4.1.4.1.1  Base Reflectivity Use … 4-4 Figure 4-4. WSR-88D Weather Radar Stratiform Precipitation on the 0.5ºBase Reflectivity Product Example … 4-5 Figure 4-5. WSR-88D Weather Radar Convective Precipitation on the 0.5ºBase Reflectivity Product Example … 4-5 4.1.4.1.2  Strengths of Base Reflectivity … 4-6 4.1.4.1.3  Limitations of Base Reflectivity … 4-6 4.1.4.1.3.1  Radar Beam Overshooting … 4-6 4.1.4.1.3.2  Beam Blockage … 4-6 Figure 4-6. WSR-88D Weather Radar Beam Blockage on Base Reflectivity Product Example … 4-7 4.1.4.1.3.3  Ground Clutter … 4-7 Figure 4-8. WSR-88D Weather Radar Ground Clutter Example … 4-7 4.1.4.1.3.4  Ghost … 4-8 Figure 4-9. WSR-88D Weather Radar Ghost Example … 4-8 4.1.4.1.3.5  Angels … 4-8 Figure 4-10. WSR-88D Weather Radar Angle Example … 4-9 4.1.4.1.3.6  Anomalous Propagation (AP) … 4-9 Figure 4-11. WSR-88D Weather Radar Anomalous Propagation (AP) Example … 4-10 4.1.4.2  Composite Reflectivity … 4-10 Figure 4-12. Creation of a Composite Reflectivity product … 4-10 Figure 4-13. WSR-88D Weather Radar Long Range (248 NM) Composite Reflectivity Product Example … 4-11 Figure 4-14. WSR-88D Weather Radar Short Range (124 NM) Composite Reflectivity Product Example … 4-12 4.1.4.2.1  Composite Reflectivity Use … 4-12 Figure 4-15. WSR-88D Weather Radar 0.5º Base Reflectivity versus Composite Reflectivity Comparison … 4-13 4.1.4.2.2  Strengths of Composite Reflectivity … 4-13 4.1.4.2.3  Limitations of Composite Reflectivity … 4-13 4.1.4.2.3.1  Radar Beam Overshooting … 4-13 4.1.4.2.3.2  Beam Blockage … 4-13 4.1.4.2.3.3  Ground Clutter … 4-14 4.1.4.2.3.4  Ghost … 4-14 4.1.4.2.3.5  Angels … 4-14 4.1.4.2.3.6  Anomalous Propagation (AP) … 4-14 4.1.5  Radar Mosaics … 4-14 4.1.5.1  0.5º Mosaics - Contiguous U.S. and Hawaii … 4-15 Table 4-2. NWS Radar Mosaic Products … 4-15 Figure 4-16. Great Lakes Regional Radar Mosaic Example … 4-15 4.1.5.2  0.5º Mosaics - Alaska … 4-16 AC 00-45F, CHG 2 Table of Contents Page iv ### Page 8 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-17. Alaskan Regional Radar Mosaic Example … 4-16 4.2  SATELLITE … 4-17 4.2.1  Description … 4-17 4.2.2  Imagery Types … 4-17 4.2.2.1  Visible Imagery … 4-17 Figure 4-18. Visible Satellite Image – U.S. Example … 4-18 Figure 4-19. Visible Satellite Image – Regional-Scale Example … 4-19 4.2.2.1.1  Visible Image Data Legend … 4-19 Figure 4-20. Visible Satellite Data Legend … 4-19 4.2.2.2  Infrared (IR) Imagery … 4-19 Figure 4-21. Infrared (Color) Satellite Image – U.S. Example … 4-20 Figure 4-22. Infrared (Color) Satellite Image – Regional-Scale Example … 4-21 Figure 4-23. Unenhanced Infrared (black and white) Satellite Image – U.S. Example … 4-21 Figure 4-24. Unenhanced Infrared (black and white) Satellite Image – Regional- Scale Example . 4- 22 4.2.2.2.1  Infrared Image Data Legends … 4-22 Figure 4-25. Infrared (Color) Satellite Image Data Legend … 4-22 Figure 4-26. Unenhanced Infrared (black and while) Satellite Image Data Legend … 4-22 4.2.3.3  Water Vapor Imagery … 4-22 Figure 4-27. Water Vapor Satellite Image – U.S. Example … 4-23 Figure 4-28. Water Vapor Satellite Image – Regional-Scale Example … 4-24 4.2.3.3.1  Water Vapor Image Data Legend … 4-24 Figure 4-29. Water Vapor Satellite Image Data Legend … 4-24 5  GRAPHICAL OBSERVATIONS AND DERIVED PRODUCTS … 5-1 5.1  SURFACE ANALYSIS CHARTS … 5-1 Figure 5-1. HPC Surface Analysis Chart Example … 5-1 5.1.1  Issuance … 5-1 5.1.2  HPC Surface Analysis Charts … 5-2 5.1.2.1  Issuance … 5-2 Table 5-1. HPC Surface Analysis Charts Issuance Schedule … 5-2 5.1.2.2  Analysis Symbols … 5-2 Figure 5-2. HPC Surface Analysis Chart Symbols … 5-3 5.1.2.3  Station Plot Models … 5-3 Figure 5-3. HPC Surface Analysis Chart Station Plot Model … 5-3 Figure 5-4. HPC Surface Analysis Chart Ship/Buoy Plot Model … 5-4 Figure 5-5. HPC Surface Analysis Chart for Aviation Interests Station Plot Model … 5-4 5.1.2.3.1  Station Identifier … 5-4 5.1.2.3.2  Temperature … 5-4 5.1.2.3.3  Dew Point … 5-5 5.1.2.3.4  Weather … 5-5 Figure 5-6. HPC Surface Analysis Chart Common Weather Symbols … 5-5 5.1.2.3.5  Wind … 5-5 Figure 5-7. HPC Surface Analysis Chart Wind Plotting Model … 5-6 5.1.2.3.6  Ceiling … 5-6 5.1.2.3.7  Visibility … 5-6 5.1.2.3.8  Pressure … 5-6 5.1.2.3.9  Pressure Trend … 5-6 Figure 5-8. HPC Surface Analysis Chart Pressure Trends … 5-7 5.1.2.3.10  Sky Cover … 5-7 Figure 5-9. HPC Surface Analysis Chart Sky Cover Symbols … 5-7 5.1.2.3.11  Water Temperature … 5-7 5.1.2.3.12  Swell Information … 5-8 5.1.2.3.13  Wave Information … 5-8 5.1.2.4  Analyses … 5-8 5.1.2.4.1  Isobars … 5-8 5.1.2.4.2  Pressure Systems … 5-9 5.1.2.4.3  Fronts … 5-9 Figure 5-10. HPC Surface Analysis Chart – North America Example … 5-9 Figure 5-11. HPC Surface Analysis Chart - Contiguous U.S. Example … 5-10 Figure 5-12. HPC Surface Analysis Chart - Northeast U.S. Example … 5-10 AC 00-45F, CHG 2 Table of Contents Page v ### Page 9 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-13. HPC Surface Analysis Chart for Aviation Interests – Contiguous U.S. Example ... 5-11 Figure 5-14. HPC Surface Analysis Chart for Aviation Interests – South central U.S. Example 5-11 5.1.3  OPC and WFO Honolulu Surface Analysis Charts … 5-12 5.1.3.1  Issuance … 5-12 Table 5-2. OPC and WFO Honolulu Surface Analysis Charts Issuance Schedule … 5-12 5.1.3.2  Analysis Symbols … 5-12 Figure 5-15. OPC and WFO HNL Surface Analysis Chart Symbols … 5-12 Figure 5-16. WFO HNL Surface Analysis Chart – North Pacific Example … 5-13 5.1.3.3  Wave Information … 5-13 5.1.3.4  Analyses … 5-13 5.1.3.4.1  Isobars … 5-13 5.1.3.4.2  Pressure Systems … 5-14 5.1.3.4.3  Fronts … 5-14 5.1.4  TPC Surface Analysis Charts … 5-14 5.1.4.1  Issuance … 5-14 Table 5-3. TPC Surface Analysis Charts Issuance Schedule … 5-14 5.1.4.2  Analysis Symbols … 5-14 Figure 5-17. TPC Surface Analysis Chart Symbols … 5-15 Figure 5-18. TPC Tropical Surface Analysis Chart Example … 5-15 5.1.4.2.1  Wind … 5-15 Figure 5-19: TPC Surface Analysis Chart Wind Plotting Model … 5-16 5.1.4.3  Analyses … 5-16 5.1.4.3.1  Isobars … 5-16 5.1.4.3.2  Pressure Systems … 5-16 5.1.4.3.3  Fronts … 5-17 5.1.5  Unified Surface Analysis Chart … 5-17 5.1.5.1  Issuance … 5-17 Table 5-4. Unified Surface Analysis Chart Issuance Schedule … 5-17 Figure 5-20. Unified Surface Analysis Chart Example … 5-17 5.1.5.2  Analysis Symbols … 5-17 Figure 5-21. Unified Surface Analysis Chart Symbols … 5-18 5.1.5.3  Analyses … 5-18 5.1.5.3.1  Isobars … 5-18 5.1.5.3.2  Pressure Systems … 5-18 5.1.5.3.3  Fronts … 5-18 5.1.6  AAWU Surface Charts … 5-19 5.1.6.1  Issuance … 5-19 Table 5-5. AAWU Surface Analysis Issuance Schedule … 5-19 5.1.6.2  Analysis Symbols … 5-19 Figure 5-22. AAWU Surface Analysis Chart Symbols … 5-19 Figure 5-23. AAWU Alaskan Surface Chart Example … 5-20 5.1.6.3  Station Plot Models … 5-20 Figure 5-24. AAWU Surface Analysis Chart Station Plot Model … 5-20 Figure 5-25. AAWU Surface Analysis Chart Ship/buoy Plot Model … 5-21 5.1.6.3.1  Station Identifier … 5-21 5.1.6.3.2  Temperature … 5-21 5.1.6.3.3  Dew Point … 5-21 5.1.6.3.4  Wind … 5-21 Figure 5-26: AAWU Surface Analysis Chart Wind Plotting Model … 5-22 5.1.6.3.5  Ceiling … 5-22 5.1.6.3.6  Visibility … 5-22 5.1.6.3.7  Pressure … 5-22 5.1.6.3.8  Pressure Trend … 5-22 Figure 5-27. AAWU Surface Analysis Chart Pressure Trends … 5-23 5.1.6.3.9  Sky Cover … 5-23 Figure 5-28. AAWU Surface Analysis Chart Sky Cover Symbols … 5-23 5.1.6.3.10  Water Temperature … 5-23 5.1.6.3.11  Swell Information … 5-24 5.1.6.3.12  Wave Information … 5-24 5.1.6.4  Analyses … 5-24 5.1.6.4.1  Isobars … 5-24 5.1.6.4.2  Pressure Systems … 5-24 AC 00-45F, CHG 2 Table of Contents Page vi ### Page 10 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.6.4.3  Fronts … 5-25 5.2  CONSTANT PRESSURE CHARTS … 5-26 Figure 5-29. Constant Pressure Chart Example … 5-26 5.2.1  Issuance … 5-26 5.2.2  Observational Data … 5-26 Figure 5-30. U.S. Radiosonde Network … 5-27 Table 5-6 Features of Constant Pressure Charts … 5-28 Table 5-7. Constant Pressure Chart Plotting Models … 5-28 Table 5-8. Radiosonde Plotting Model Examples … 5-29 5.2.3  Analyses … 5-29 5.2.3.1  Height … 5-29 5.2.3.2  Temperature … 5-29 5.2.3.3  Wind Speed … 5-30 5.2.3.4  Use … 5-30 Table 5-9. Reconnaissance Aircraft (RECCO) Plotting Model Examples … 5-30 Table 5-10. Aircraft Report (AIREP) Plotting Model Examples … 5-31 Table 5-11. Satellite Wind Estimate Plotting Model Examples … 5-31 Figure 5-31. 850MB Analysis Chart Example … 5-32 Figure 5-32. 700MB Analysis Chart Example … 5-32 Figure 5-33. 500MB Analysis Chart Example … 5-33 Figure 5-34. 300MB Analysis Chart Example … 5-33 Figure 5-35. 200MB Analysis Chart Example … 5-34 5.3  FREEZING-LEVEL GRAPHICS … 5-35 5.3.1  Issuance … 5-35 5.3.2  Observational Data … 5-35 5.3.3  Format … 5-36 Figure 5-36. RUC 00-hour Freezing Level Graphic Example … 5-37 5.3.4  Use … 5-38 Figure 5-37. ADDS Freezing Level Graphic Example … 5-38 5.4  LIFTED INDEX ANALYSIS CHART … 5-39 Figure 5-38. Lifted Index Analysis Chart Example … 5-39 5.4.1  Issuance … 5-39 5.4.2  Lifted Index (LI) … 5-39 5.4.2.1  Data Plot … 5-40 5.4.2.2  Analysis … 5-40 5.4.2.3  Use of Lifted Index … 5-40 5.4.3  K Index … 5-40 5.4.3.1  Data Plot … 5-40 5.4.3.2  Use of K Index … 5-40 Table 5-12. K Index and Coverage of General Thunderstorms … 5-41 5.5  WEATHER DEPICTION CHART … 5-42 Figure 5-39. Weather Depiction Chart Example … 5-42 5.5.1  Issuance … 5-42 Table 5-13. Weather Depiction Charts Issuance Schedule … 5-42 5.5.2  Station Plot Model … 5-42 Figure 5-40. Weather Depiction Chart Station Plot Model … 5-43 5.5.2.1  Visibility … 5-43 5.5.2.2  Present Weather … 5-43 5.5.2.3  Sky Cover … 5-43 5.5.2.4  Ceiling … 5-43 5.5.3  Weather Flying Category Analysis … 5-44 5.5.4  Use … 5-44 5.6  ALASKA WEATHER DEPICTION CHARTS … 5-45 Figure 5-41. AAWU Alaska Weather Depiction Chart Example … 5-45 Table 5-14. AAWU Alaska Weather Depiction Charts Coverage … 5-46 5.6.1  Issuance … 5-46 5.6.2  Legends … 5-46 5.6.2.1  Flying Category … 5-46 Table 5-15 AAWU Alaska Weather Flying Categories and Criteria … 5-46 5.6.2.2  Station Plot … 5-46 AC 00-45F, CHG 2 Table of Contents Page vii ### Page 11 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-42. AAWU Alaska Weather Depiction Chart Station Plot Legend … 5-46 5.6.2.3  Sky Cover … 5-47 5.6.2.4  Station Identifier (STNID) … 5-47 5.6.2.5  Wind … 5-47 Figure 5-43. AAWU Alaska Weather Depiction Chart Wind Symbols … 5-47 5.6.2.6  Temperature (TMP deg F) … 5-47 5.6.2.7  Visibility (VIS) … 5-47 5.6.2.8  Dew Point Temperature (DEWPT deg F) … 5-48 5.6.2.9  Ceiling (CIG) … 5-48 5.6.2.10  Present Weather (WX) … 5-48 Table 5-16 Alaska Weather Depiction Charts Precipitation Symbols … 5-48 Table 5-17 Alaska Weather Depiction Charts Obstruction to Visibility Symbols … 5-48 Table 5-18 Alaska Weather Depiction Charts Precipitation Intensity Symbols … 5-48 5.6.3  Use … 5-49 Figure 5-44. AAWU Alaska Weather Depiction Chart – South Central Alaska Example … 5-49 5.7  RADAR SUMMARY CHART … 5-50 Figure 5-45. Radar Summary Chart Example … 5-50 5.7.1  Issuance … 5-50 5.7.2  Format … 5-50 5.7.2.1  Precipitation Type … 5-50 Table 5-19. Radar Summary Chart Precipitation Type Symbols … 5-51 5.7.2.2  Precipitation Intensity … 5-51 Figure 5-46. WSR-88D Weather Radar Network … 5-51 Figure 5-47. Radar Summary Chart Precipitation Intensity … 5-52 5.7.2.3  Echo Coverage … 5-52 5.7.2.4  Line Echoes … 5-52 Table 5-20. Radar Summary Chart Echo Configuration Symbols … 5-52 5.7.2.5  Cell Movement … 5-52 Table 5-21. Radar Summary Chart Cell Movement Examples … 5-53 5.7.2.6  Maximum Top … 5-53 Figure 5-48. Radar Summary Chart Maximum Top Example … 5-53 5.7.2.7  Weather Watch Areas … 5-54 Table 5-22. Radar Summary Chart Weather Watch Area Examples … 5-54 5.7.2.8  Operational Contractions … 5-54 Table 5-23. Radar Summary Chart Operational Contractions … 5-54 5.7.3  Use … 5-54 Figure 5-49. Radar Summary Chart Example … 5-55 5.8  ALASKA INITIAL GEOPOTENTIAL HEIGHTS AND WINDS CHARTS … 5-56 Figure 5-50. Alaskan Initial Geopotential Heights and Winds Chart Example … 5-56 Table 5-24. Pressure Altitudes of Alaska Initial Geopotential Heights and Winds Charts … 5-56 5.8.1  Issuance … 5-56 5.8.2  Analysis … 5-57 5.8.2.1  Height Contours … 5-57 5.8.2.2  Winds … 5-57 Figure 5-51. Alaskan Initial Geopotential Heights and Winds Chart Wind Plotting Model … 5-57 5.8.3  Use … 5-57 Figure 5-52. Alaskan Initial Geopotential Heights and Winds Chart - 200MB Winds and Contours Chart Example … 5-59 Figure 5-53. Alaskan Initial Geopotential Heights and Winds Chart - 300MB Winds and Contours Chart Example … 5-59 Figure 5-54. Alaskan Initial Geopotential Heights and Winds Chart - 500MB Winds and Contours Chart Example … 5-60 Figure 5-55. Alaskan Initial Geopotential Heights and Winds Chart - 700MB Winds and Contours Chart Example … 5-60 Figure 5-56. Alaskan Initial Geopotential Heights and Winds Chart - 850MB Winds and Contours Chart Example … 5-61 6  PRODUCTS FOR AVIATION HAZARDS … 6-1 6.1  SIGNIFICANT METEOROLOGICAL INFORMATION (SIGMET) … 6-1 6.1.1  SIGMET Issuance … 6-1 Figure 6-1. AWC SIGMET Areas of Responsibility - Conterminous U.S … 6-2 AC 00-45F, CHG 2 Table of Contents Page viii ### Page 12 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-2. AWC SIGMET Areas of Responsibility – Atlantic Basin … 6-2 Figure 6-3. SIGMET Areas of Responsibility – Pacific Basin … 6-3 6.1.1.1  SIGMET Identification … 6-3 6.1.2  SIGMET Standardization … 6-4 6.1.3  SIGMET (Non-Convective) – Conterminous U.S … 6-4 6.1.3.1  SIGMET (Non-Convective) Issuance Criteria – Contiguous U.S … 6-4 6.1.3.2  SIGMET (Non-Convective) Issuance Time and Valid Period – Conterminous U.S … 6-5 6.1.3.3  SIGMET (Non-Convective) Format – Conterminous U.S … 6-5 Figure 6-4. SIGMET for the Conterminous U.S. Decoding Example … 6-6 Table 6-1. Decoding a SIGMET (Non-Convective) for the Conterminous U.S … 6-6 6.1.3.4  SIGMET (Non-Convective) Cancellations – Conterminous U.S … 6-7 6.1.3.5  SIGMET (Non-Convective) Amendments – Conterminous U.S … 6-7 6.1.3.6  SIGMET (Non-Convective) Corrections – Conterminous U.S … 6-7 6.1.3.7  SIGMET (Non-Convective) Example – Conterminous U.S … 6-7 6.1.4  Convective SIGMET … 6-7 6.1.4.1  Convective SIGMET - Routine Issuance Criteria … 6-7 6.1.4.2  Convective SIGMET - Special Issuance Criteria … 6-8 6.1.4.3  Convective SIGMET Issuance Time and Valid Period … 6-8 Figure 6-5. AWC Convective SIGMET Areas of Responsibility … 6-8 6.1.4.4  Convective SIGMET Format … 6-9 Figure 6-6. Convective SIGMET Decoding Example … 6-10 Table 6-2. Decoding a Convective SIGMET … 6-10 6.1.4.5  Convective SIGMET Outlook … 6-11 6.1.4.6  Convective SIGMET Cancellations … 6-11 6.1.4.7  Convective SIGMET Amendments … 6-11 6.1.4.8  Convective SIGMET Corrections … 6-11 6.1.4.9  Convective SIGMET Bulletin Examples … 6-11 6.1.4.9.1  Convective SIGMET Bulletin – Tropical Cyclone Example … 6-12 6.1.5  SIGMET – Outside the Conterminous U.S. (O-CONUS) … 6-13 6.1.5.1  SIGMET Issuance Criteria – Outside the Conterminous U.S. (O-CONUS) … 6-14 6.1.5.2  SIGMET Issuance Time and Valid Period – Outside the Conterminous U.S. (O-CONUS) … 6-14 6.1.5.3  SIGMET Format – Outside the Conterminous U.S. (O-CONUS) … 6-14 Figure 6-7. SIGMET Outside the Conterminous U.S. Decoding Example … 6-16 Table 6-3. Decoding a SIGMET Outside of the Conterminous U.S. (O-CONUS) … 6-16 6.1.5.4  SIGMETs for Volcanic Ash … 6-17 6.1.5.5  SIGMETs for Tropical Cyclone … 6-17 6.1.5.6  SIGMET Cancellation– Outside the Conterminous U.S. (O-CONUS) … 6-17 6.1.5.7  SIGMET Amendments– Outside the Conterminous U.S. (O-CONUS) … 6-17 6.1.5.8  SIGMET Corrections– Outside the Conterminous U.S. (O-CONUS) … 6-17 6.1.5.9  SIGMET Example– Outside the Conterminous U.S. (O-CONUS) … 6-18 6.1.5.9.1  SIGMET for Volcanic Ash Example … 6-18 6.1.5.9.2  SIGMET for Tropical Cyclone Example … 6-18 6.2  AIRMEN’S METEOROLOGICAL INFORMATION (AIRMET) … 6-20 6.2.1  AIRMET Issuance … 6-20 Figure 6-8 AWC AIRMET Areas of Responsibility – Conterminous U.S … 6-21 Figure 6-9. AAWU Flight Advisory and Area Forecast Zones - Alaska … 6-22 Table 6-4. AAWU Flight Advisory and Area Forecast Zones – Alaska … 6-22 Figure 6-10. WFO Honolulu AIRMET Areas of Responsibility - Hawaii … 6-23 6.2.2  AIRMET Issuance Criteria … 6-23 6.2.3  AIRMET Standardization … 6-24 6.2.4  AIRMET Bulletins, Issuance Times, and Valid Period … 6-24 Table 6-5. AIRMET Issuance Schedule … 6-24 6.2.5  AIRMET Format … 6-25 Figure 6-11. AIRMET Bulletin Decoding Example … 6-26 Table 6-6. Decoding an AIRMET Bulletin … 6-26 6.2.5.1  AIRMET Updates and Amendments … 6-27 6.2.5.2  AIRMET Corrections … 6-27 6.2.6  AIRMET Examples … 6-27 6.2.6.1  CONUS AIRMET Example … 6-27 6.2.6.2  Hawaii AIRMET Example … 6-28 6.2.6.3  Alaska AIRMET Example … 6-29 AC 00-45F, CHG 2 Table of Contents Page ix ### Page 13 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.3  CENTER WEATHER ADVISORY (CWA) … 6-31 6.3.1  CWA Issuance … 6-31 Figure 6-12. Center Weather Service Unit (CWSU) Areas of Responsibility, Contiguous U.S. .. 6-31 Figure 6-13. CWSU Anchorage, AK (PAZA) Area of Responsibility … 6-32 6.3.2  CWA Communications Headers (UCWA / CWA) … 6-32 6.3.3  CWA Criteria … 6-32 6.3.4  CWA Format … 6-33 Figure 6-14. Center Weather Advisory (CWA) Decoding Example … 6-33 Table 6-7. Decoding a Center Weather Advisory (CWA) … 6-33 6.3.5  Examples … 6-34 6.4  ADDITIONAL PRODUCTS FOR CONVECTION … 6-37 6.4.1  Convective Outlooks (AC) … 6-37 6.4.1.1  Issuance … 6-37 Table 6-8. Convective Outlook Issuance Schedule … 6-37 Figure 6-15. Day 1 Categorical Convective Outlook Graphic Example … 6-38 6.4.1.2  Format of the Categorical Convective Outlook Narrative … 6-38 6.4.2  Watch Notification Messages … 6-39 6.4.2.1  Aviation Watch Notification Message … 6-39 6.4.2.1.1  Format of an Aviation Watch Notification Message … 6-39 Figure 6-16. Aviation Watch Notification Message Decoding Example … 6-40 Table 6-9. Decoding a Severe Weather Watch Bulletin … 6-40 6.4.2.1.2  Issuance … 6-41 6.4.3  Public Severe Thunderstorm Watch Notification Message … 6-41 6.4.3.1  Format of Public Severe Thunderstorm Watch Notification Message … 6-41 6.4.3.2  Example of a Public Severe Thunderstorm Watch Notification Message … 6-42 6.4.4  Public Tornado Watch Notification Message … 6-43 6.4.4.1  Format of a Public Tornado Watch Notification Message … 6-44 6.4.4.2  Example of a Public Tornado Watch Notification Message … 6-44 6.5  PRODUCTS FOR TROPICAL CYCLONES … 6-46 6.5.1  Aviation Tropical Cyclone Advisory (TCA) … 6-46 6.5.1.1  Issuance … 6-46 6.5.1.2  Content … 6-46 6.5.1.3  Format … 6-46 6.5.1.4  Aviation Tropical Cyclone Advisory (TCA) Example … 6-47 6.5.2  Tropical Cyclone Public Advisory (TCP) … 6-47 6.5.2.1  TCP Responsibility … 6-47 6.5.2.2  TCP Issuance … 6-48 Table 6-10. Tropical Cyclone Public Advisory Issuance Schedule … 6-48 6.5.2.2.1  TCP Intermediate Issuances … 6-49 Table 6-11. Intermediate Tropical Cyclone Public Advisory Issuance Schedule … 6-49 6.5.2.3  TCP Content … 6-49 6.5.2.4  TCP Format … 6-50 6.5.2.5  Tropical Storm Public Advisory (TCP) Example … 6-51 6.5.2.6  Hurricane/Typhoon Public Advisory Example … 6-51 6.5.2.7  Intermediate Public Advisory Example … 6-53 6.5.2.8  Special Public Advisory Example … 6-55 6.5.2.9  Public Advisory Correction Example … 6-56 6.6  VOLCANIC ASH ADVISORY PRODUCTS … 6-57 6.6.1  Volcanic Ash Advisory Center (VAAC) … 6-57 Figure 6-17. Volcanic Ash Advisory Centers (VAACs) Area of Responsibility … 6-57 6.6.2  Volcanic Ash Advisory Statement (VAAS) … 6-58 6.6.2.1  Issuance … 6-58 6.6.2.2  Format … 6-58 6.6.2.3  VAAS Issued by the Washington VAAC Example … 6-58 6.6.3  Volcanic Ash Advisory (VAA) … 6-59 6.6.3.1  VAA Issuance … 6-59 6.6.3.2  VAA Format … 6-59 6.6.3.3  Volcanic Ash Advisory (VAA) Example … 6-59 7  FORECAST TEXT PRODUCTS … 7-1 AC 00-45F, CHG 2 Table of Contents Page x ### Page 14 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 7.1  AREA FORECASTS (FA) … 7-1 7.1.1  Area Forecast Issuance … 7-1 Figure 7-1. AWC Area Forecast Regions- Contiguous U.S … 7-2 Figure 7-2. AWC Area Forecast Region and WMO Header - Gulf of Mexico … 7-2 Figure 7-3. AWC Area Forecast Region and WMO Header - Caribbean … 7-3 Figure 7-4. WFO Honolulu Area Forecast Region and WMO header - Hawaii … 7-3 Figure 7-5. AAWU Flight Advisory and Area Forecast Zones - Alaska … 7-4 Table 7-1. AAWU Area Forecast Zones – Alaska … 7-4 7.1.2  Area Forecast Standardization … 7-4 7.1.3  Area Forecast Issuance Schedule … 7-5 Table 7-2. Area Forecast (FA) Issuance Schedule … 7-5 7.1.4  Area Forecast Amendments … 7-5 7.1.5  Area Forecast Corrections … 7-6 7.1.6  Area Forecast Format – Conterminous U.S. (CONUS) … 7-6 Figure 7-6. Area Forecast – CONUS Communication and Product Header Example … 7-7 Table 7-3. Decoding a CONUS Area Forecast Communication and Product Header … 7-7 Figure 7-7. Area Forecast - Clouds and Weather Element Example … 7-8 7.1.6.1  Area Forecast – Conterminous U.S. (CONUS) Examples … 7-8 7.1.6.1.1  Area Forecast – BOS Example … 7-8 7.1.6.1.2  Area Forecast – SFO (FA) Example … 7-10 7.1.7  Area Forecast Format – Gulf of Mexico (FAGX) … 7-12 7.1.7.1  Area Forecast – Gulf of Mexico (FAGX) Example … 7-13 7.1.8  Area Forecast Format – Caribbean (FACA) … 7-13 7.1.8.1  Area Forecast – Caribbean (FACA) Example … 7-14 7.1.9  Area Forecast Format - Hawaii … 7-15 7.1.9.1  Area Forecast – Hawaii Example … 7-15 7.1.10  Area Forecast Format - Alaska … 7-16 7.1.10.1  Area Forecast – Alaska Example … 7-17 7.2  TERMINAL AERODROME FORECAST (TAF) … 7-19 7.2.1  Responsibility … 7-19 7.2.2  Generic Format of the Forecast Text of a NWS-Prepared TAF … 7-19 7.2.2.1  Type of Report (TAF or TAF AMD or TAF COR) … 7-19 7.2.2.2  Location Identifier (CCCC) … 7-20 7.2.2.3  Date/Time of Forecast Origin Group (YYGGggZ) … 7-20 7.2.2.4  Valid Period (Y1Y1G1G1/Y2Y2G2G2) … 7-20 7.2.2.5  Wind Group (dddffGfmfmKT) … 7-21 7.2.2.6  Visibility Group (VVVV) … 7-22 7.2.2.7  Significant Weather Group (w'w' or NSW) … 7-22 7.2.2.7.1  Exception for Encoding Multiple Precipitation Types … 7-23 7.2.2.7.2  Thunderstorm Descriptor … 7-24 7.2.2.7.3  Fog Forecast … 7-24 Table 7-5. TAF Fog Terms … 7-25 7.2.2.8  Vicinity (VC) … 7-25 Table 7-6: TAF Use of Vicinity (VC) … 7-25 7.2.2.9  Cloud and Vertical Obscuration Groups (NsNsNshshshs or VVhshshs or SKC) … 7-26 7.2.2.9.1  Cloud Group (NsNsNshshshs) … 7-26 Table 7-7. TAF Sky Cover … 7-26 7.2.2.9.2  Vertical Obscuration Group (VVhshshs) … 7-26 7.2.2.9.3  Cloud Type (CB) … 7-26 7.2.2.10  Non-Convective Low-Level Wind Shear (LLWS) Group (WShwshwshws/dddffKT) … 7-27 7.2.2.11  Forecast Change Indicator Groups … 7-28 7.2.2.11.1  From (FM) Group (FMYYGGgg) … 7-28 7.2.2.11.2  TEMPO (YYGG/YeYeGeGe) Group … 7-29 7.2.2.11.3  PROB30 (YYGG/YeYeGeGe) Group … 7-30 7.2.2.12  TAF Examples … 7-31 7.2.3  Issuance … 7-33 Table 7-8. TAF Issuance Schedule … 7-33 7.2.3.1  Minimum Observational Requirements for Routine TAF Issuance and Continuation … 7-34 7.2.3.2  Sites with Scheduled Part-Time Observations … 7-34 7.2.3.2.1  Examples of Scheduled Part-Time Observations TAFs … 7-34 AC 00-45F, CHG 2 Table of Contents Page xi ### Page 15 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 7.2.3.3  Automated Observing Sites Requiring Part-Time Augmentation … 7-35 7.2.3.4  Non-Augmented Automated Observing Sites … 7-35 7.3  INTERNATIONAL AVIATION ROUTE FORECASTS (ROFOR) … 7-36 7.3.1  ROFOR Criteria … 7-36 7.3.2  Issuance … 7-36 7.3.2.1  ROFOR Amendments … 7-36 7.3.2.2  ROFOR Corrections … 7-36 7.3.3  ROFOR Content … 7-36 7.3.4  ROFOR Examples … 7-37 7.3.4.1  Majuro to Kwajalein Route ROFOR Example … 7-37 7.3.4.2  Tarawa to Majuro Route ROFOR Example … 7-37 7.3.4.3  Santa Barbara and San Francisco to Honolulu Route ROFOR Example … 7-37 7.4  WIND AND TEMPERATURE ALOFT FORECAST (FB) … 7-39 7.4.1  Forecast Altitudes … 7-39 Table 7-9. Wind and Temperature Aloft Forecast Levels … 7-39 7.4.2  Format … 7-39 7.4.2.1  Coding Example … 7-40 Table 7-10. Wind and Temperature Aloft Forecast Decoding Examples … 7-41 7.4.2.2  Example for the Contiguous US and Alaska … 7-41 7.4.2.3  Example for Hawaii and the Western Pacific … 7-41 7.4.3  Issuance … 7-42 Figure 7-8. Wind and Temperature Aloft Forecast Network - Contiguous US … 7-42 Figure 7-9. Wind and Temperature Aloft Forecast Network - Alaska … 7-43 Figure 7-10. Wind and Temperature Aloft Forecast Network - Hawaii … 7-43 Figure 7-11. Wind and Temperature Aloft Forecast Network - Western Pacific … 7-44 Table 7-11. Wind and Temperature Aloft Forecast (FB) Periods … 7-44 7.4.4  Delayed Forecasts … 7-44 8  FORECAST CHARTS … 8-1 8.1  SHORT-RANGE SURFACE PROGNOSTIC (PROG) CHARTS … 8-1 Figure 8-1. Surface Prog Chart Example … 8-1 8.1.1  Content … 8-2 Figure 8-2. Surface Prog Chart Symbols … 8-2 8.1.1.1  Pressure Systems … 8-2 8.1.1.2  Fronts … 8-2 8.1.1.3  Squall Lines … 8-2 8.1.1.4  Precipitation … 8-2 Figure 8-3. Surface Prog Chart Precipitation Symbols … 8-3 Figure 8-4. Surface Prog Chart Precipitation Example … 8-3 Figure 8-5. Surface Prog Chart Precipitation Coverage … 8-4 8.1.2  Issuance … 8-4 Table 8-1. Short-Range Surface Prog Charts Schedule … 8-4 8.1.3  Use … 8-4 Figure 8-6. 12-hour Surface Prog Chart Example … 8-5 Figure 8-7. 24-hour Surface Prog Chart Example … 8-5 Figure 8-8. 36-hour Surface Prog Chart Example … 8-6 Figure 8-9. 48-hour Surface Prog Chart Example … 8-7 8.2  LOW-LEVEL SIGNIFICANT WEATHER (SIGWX) CHARTS … 8-8 Figure 8-10. 12-Hour Low-Level SIGWX Chart Example … 8-8 8.2.1  Content … 8-8 Figure 8-11. Low-Level SIGWX Chart Symbols … 8-9 8.2.1.1  Flying Categories … 8-9 Figure 8-12. Low-Level SIGWX Chart Flying Categories Example … 8-9 8.2.1.2  Turbulence … 8-9 Figure 8-13. Low-Level SIGWX Chart Turbulence Forecast Example … 8-10 8.2.1.3  Freezing Levels … 8-10 Figure 8-14. Low-Level SIGWX Chart Freezing Level Forecast Example … 8-11 Figure 8-15. Low-Level SIGWX Chart Multiple Freezing Levels Example … 8-11 8.2.2  Issuance … 8-12 8.2.3  Use … 8-12 AC 00-45F, CHG 2 Table of Contents Page xii ### Page 16 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 8-16. 12-Hour Low-Level SIGWX Chart Example … 8-12 Figure 8-17. 24-hour Low-Level SIGWX Chart Example … 8-13 8.3  MID-LEVEL SIGNIFICANT WEATHER (SIGWX) CHART … 8-14 Figure 8-18. Mid-Level SIGWX Chart Example … 8-14 8.3.1  Content … 8-14 8.3.1.1  Thunderstorms … 8-14 Table 8-3. Mid-Level SIGWX Chart Cumulonimbus Coverage … 8-15 Figure 8-19. Mid-Level SIGWX Chart Thunderstorm Examples … 8-15 8.3.1.2  Surface Frontal Positions and Movements … 8-16 Figure 8-20. Mid-Level SIGWX Chart Surface Frontal Position and Movement Example … 8-16 8.3.1.3  Jet Streams … 8-16 Figure 8-21. Mid-Level SIGWX Chart Jet stream Example … 8-16 8.3.1.4  Tropopause Heights … 8-17 Figure 8-22. Mid-Level SIGWX Chart Tropopause Height Examples … 8-17 8.3.1.5  Tropical Cyclones … 8-17 Figure 8-23. Mid-Level SIGWX Chart Tropical Cyclone Examples … 8-17 8.3.1.6  Moderate or Severe Icing … 8-17 Figure 8-24. Mid-Level SIGWX Chart Icing Examples … 8-18 8.3.1.7  Moderate or Severe Turbulence (in cloud or in clear air) … 8-18 Figure 8-25. Mid-Level SIGWX Chart Turbulence Examples … 8-18 8.3.1.8  Cloud Coverage (non-cumulonimbus) … 8-19 Table 8-4. Mid-Level SIGWX Chart Cloud Coverage (Non-cumulonimbus) … 8-19 8.3.1.9  Cloud Type … 8-19 Table 8-5. Mid-Level SIGWX Chart Cloud Types … 8-19 Figure 8-26. Mid-Level SIGWX Chart - Example of Moderate or Severe Icing, Moderate or Severe Turbulence (in cloud or in clear air), Clouds, and Cloud Types … 8-20 8.3.1.10  Volcanic Eruptions … 8-20 Figure 8-27. Mid-Level SIGWX Chart Volcanic Eruption Example … 8-20 8.3.1.11  Release of Radioactive Materials … 8-20 Figure 8-28. Mid-Level SIGWX Chart Release of Radioactive Materials Example … 8-20 8.3.2  Issuance … 8-20 Table 8-6. Mid-Level SIGWX Chart Issuance Schedule … 8-21 8.3.3  Use … 8-21 Figure 8-29. Mid-Level SIGWX Chart Example … 8-22 8.4  HIGH-LEVEL SIGNIFICANT WEATHER (SIGWX) CHARTS … 8-23 Figure 8-30. High-level SIGWX Chart Example … 8-23 8.4.1  Content … 8-24 8.4.1.1  Thunderstorms and Cumulonimbus Clouds … 8-24 Figure 8-31. High-Level SIGWX Chart Thunderstorm and Cumulonimbus Cloud Examples... 8-24 8.4.1.2  Moderate or Severe Turbulence … 8-25 Figure 8-32. High-Level SIGWX Chart Turbulence Examples … 8-25 8.4.1.3  Moderate or Severe Icing … 8-25 8.4.1.4  Jet Streams … 8-25 Figure 8-33. High-Level SIGWX Chart Jet stream Example … 8-26 8.4.1.5  Surface Fronts with Speed and Direction of Movement … 8-26 Figure 8-34. High Level SIGWX Chart Surface Front with Speed and Direction of Movement Example … 8-26 8.4.1.6  Tropopause Heights … 8-26 Figure 8-35. High-Level SIGWX Chart Tropopause Height Examples … 8-27 8.4.1.7  Tropical Cyclones … 8-27 Figure 8-36. High Level SIGWX Chart Tropical Cyclone Examples … 8-27 8.4.1.8  Severe Squall Lines … 8-27 Figure 8-37. High-Level SIGWX Chart Severe Squall Line Example … 8-27 8.4.1.9  Volcanic Eruption Sites … 8-28 Figure 8-38. High-Level SIGWX Chart Volcanic Eruption Site Example … 8-28 8.4.1.10  Widespread Sandstorms and Dust storms … 8-28 Figure 8-39. High-Level SIGWX Chart Widespread Sandstorm and Dust Storm Example … 8-28 8.4.2  Issuance … 8-28 Table 8-7. High-Level SIGWX Chart Issuance Schedule – WAFC Washington … 8-29 8.4.3  Use … 8-29 Figure 8-40. High-Level SIGWX Chart - ICAO Area A Example … 8-30 AC 00-45F, CHG 2 Table of Contents Page xiii ### Page 17 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 8-41. High-Level SIGWX Chart - ICAO Area B1 Example … 8-31 Figure 8-42. High-Level SIGWX Chart - ICAO Area F Example … 8-31 Figure 8-43. High-Level SIGWX Chart - ICAO Area H Example … 8-32 Figure 8-44. High-Level SIGWX Chart - ICAO Area I Example … 8-32 Figure 8-45. High-Level SIGWX Chart - ICAO Area J Example … 8-33 Figure 8-46. High-Level SIGWX Chart - ICAO Area M Example … 8-33 9  SUPPLEMENTARY PRODUCTS … 9-1 9.1  COLLABORATIVE CONVECTIVE FORECAST PRODUCT (CCFP) … 9-1 Figure 9-1. CCFP Example … 9-1 9.1.1  Issuance … 9-2 9.1.2  Collaboration … 9-2 9.1.3  Content … 9-2 9.1.3.1  Coverage … 9-2 Figure 9-2. CCFP Forecast Convective Coverage … 9-3 9.1.3.2  Confidence … 9-3 Figure 9-3. CCFP Forecast Confidence … 9-3 9.1.3.3  Movement … 9-3 Figure 9-4. CCFP Forecast Convective Movement … 9-4 9.1.3.4  Data Block … 9-4 Figure 9-5. CCFP Data Block … 9-4 Figure 9-6. CCFP Data Block Example … 9-5 9.1.3.4.1  Tops … 9-5 Table 9-1. CCFP Tops … 9-5 9.1.3.4.2  Growth … 9-5 Table 9-2. CCFP Growth … 9-5 9.1.3.4.3  Confidence … 9-5 Table 9-3. CCFP Confidence … 9-5 9.1.3.4.4  Coverage … 9-5 Table 9-4. CCFP Coverage … 9-6 9.1.4  Strengths and Limitations … 9-6 9.1.5  Use … 9-6 9.2  NATIONAL CONVECTIVE WEATHER FORECAST (NCWF) … 9-7 9.2.1  Issuance … 9-7 9.2.2  Content … 9-7 Figure 9-7. NCWF Example … 9-7 9.2.2.1  Current Convective Hazard Fields … 9-8 Figure 9-8. NCWF Current Convective Hazard Fields Example … 9-8 9.2.2.1.1  Convective Hazard Field Scale … 9-8 Figure 9-9. NCWF Hazard Scale … 9-9 9.2.2.2  One-Hour Extrapolated Forecast Polygons … 9-9 9.2.2.3  Forecast Speed and Direction … 9-9 9.2.2.4  Echo Tops … 9-9 Figure 9-10. NCWF One-Hour Extrapolated Forecast Polygon, Forecast Movement Velocity, and Echo Tops Example … 9-10 9.2.2.5  Previous Performance Polygons … 9-10 Figure 9-11. NCWF Previous Performance Polygons Example … 9-11 9.2.3  The ADDS and AWC JAVA display … 9-11 9.2.4  Strengths and Limitations … 9-11 9.2.5  Uses of the NCWF … 9-12 9.3  CURRENT ICING PRODUCT (CIP) … 9-13 9.3.1  Issuance … 9-13 9.3.2  Content … 9-13 9.3.2.1  Icing Probability … 9-14 Figure 9-12. CIP Icing Probability (3,000 feet MSL) Example … 9-14 9.3.2.2  Icing Probability -- Maximum … 9-15 Figure 9-13. CIP Icing Probability – Max Example … 9-15 9.3.2.3  Icing Severity … 9-16 Figure 9-14. CIP Icing Severity (3,000 feet MSL) Example … 9-16 9.3.2.4  Icing Severity -- Maximum … 9-17 AC 00-45F, CHG 2 Table of Contents Page xiv ### Page 18 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 9-15. CIP Icing Severity – Max Example … 9-17 9.3.2.5  Icing Severity – Probability > 25% … 9-17 Figure 9-16. CIP Icing Severity Probability >25% Example … 9-18 9.3.2.6  Icing Severity – Probability > 25% - Maximum … 9-18 Figure 9-17. CIP Icing Severity Probability >25% Example … 9-19 9.3.2.7  Icing Severity – Probability > 50% … 9-19 Figure 9-18. CIP Icing Severity Probability > 50% Example … 9-20 9.3.2.8  Icing Severity – Probability > 50% - Maximum … 9-20 Figure 9-19. CIP Icing Severity Probability > 50% - Max Example … 9-21 9.3.2.9  Icing Severity plus Supercooled Large Droplets (SLD) … 9-21 Figure 9-20. CIP Icing Severity plus Supercooled Large Droplets (SLD) Example … 9-22 9.3.2.10  Icing Severity plus Supercooled Large Droplets (SLD) - Maximum … 9-23 Figure 9-21. CIP Icing Severity plus Supercooled Large Droplets (SLD) – Max Example … 9-23 9.3.3  Strengths and Limitations … 9-24 9.3.3.1  Strengths … 9-24 9.3.3.2  Limitations … 9-24 9.3.4  Uses … 9-24 9.4  FORECAST ICING POTENTIAL (FIP) … 9-25 9.4.1  Issuance … 9-25 9.4.2  Content … 9-25 Figure 9-22. FIP Example … 9-26 9.4.3  Strengths and Limitations … 9-26 9.4.4  Use … 9-27 9.5  GRAPHICAL TURBULENCE GUIDANCE (GTG) … 9-28 9.5.1  Issuance … 9-28 9.5.2  Content … 9-28 9.5.2.1  GTG Analysis and Forecast … 9-28 Figure 9-23. GTG Example … 9-29 9.5.2.2  GTG Composite Analysis and Forecast … 9-29 Figure 9-24. GTG Composite Example … 9-30 9.5.3  Strengths and Limitations … 9-30 9.5.4  Use … 9-31 9.6  METEOROLOGICAL IMPACT STATEMENT (MIS) … 9-32 9.6.1  Valid Period … 9-32 9.6.2  MIS Criteria … 9-32 9.6.3  MIS Issuance … 9-33 9.6.4  Format … 9-33 Figure 9-25. Meteorological Impact Statement (MIS) Decoding Example … 9-33 Table 9-5. Meteorological Impact Statement (MIS) – Decoding … 9-33 9.6.5  Examples … 9-34 Figure 9-26. Center Weather Service Unit (CWSU) Areas of Responsibility - CONUS … 9-35 Figure 9-27. CWSU Anchorage, AK (PAZA) Area of Responsibility … 9-35 10 APPENDIX A: DEFINITION OF COMMON TERMS USED IN EN ROUTE FORECASTS AND ADVISORIES … 10-1 11  APPENDIX B: CONTRACTIONS AND ACRONYMS … 11-1 12  APPENDIX C: STANDARD CONVERSION CHART … 12-1 Figure C-1. Standard Conversion Chart … 12-1 13  APPENDIX D: DENSITY ALTITUDE CALCULATION … 13-1 Figure D-1. Density Altitude Computation Chart … 13-1 14  APPENDIX E: INTERNET LINKS … 14-1 Table E-1. Selected National Weather Service (NWS) Links … 14-1 Table E-2. Selected Federal Aviation Administration (FAA) Links … 14-1 Table E-3. Selected Links to Aviation Weather Products … 14-2 AC 00-45F, CHG 2 Table of Contents Page xv ### Page 19 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Table of Contents Page xvi 15  APPENDIX F: AWC ADVISORY PLOTTING CHART … 15-1 Figure F-1. AWC Advisory Plotting Chart … 15-1 16  APPENDIX G: WSR-88D WEATHER RADAR NETWORK … 16-1 Figure G-1. WSR-88D Weather Radar Network Sites … 16-1 Table G-1. WSR-88D Weather Radar Network … 16-2 17  APPENDIX H: AWC GEOGRAPHICAL AREA DESIGNATOR MAP … 17-1 Figure H-1: AWC Geographical Area Designator Map … 17-1 18  APPENDIX I: PRESENT WEATHER SYMBOLS … 18-1 Figure I-1. Present Weather Symbols with Text Explanation … 18-1 Figure I-2. Present Weather Symbols with Corresponding METAR/SPECI Present Weather Code . … 18-2 19  APPENDIX J: TURBULENCE AND ICING INTENSITY DEPICTIONS … 19-1 Table J-1. Turbulence Intensity … 19-1 Table J-2. Icing Intensity … 19-1 NOTE: CLICK ON ANY ENTRY IN THE OF THE TABLE OF CONTENTS TO JUMP DIRECTLY TO THAT SECTION. ### Page 20 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 1 AVIATION WEATHER SERVICE PROGRAM The aviation weather service program is a joint effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), the Department of Defense (DOD), and other aviation-oriented groups and individuals. This section discusses the civilian agencies of the U.S. Government and their observation, communication and forecast services to the aviation community. 1.1 National Oceanic and Atmospheric Administration (NOAA) The National Oceanic and Atmospheric Administration (NOAA) is an agency of the Department of Commerce (DOC). NOAA conducts research and gathers data about the global oceans, atmosphere, space, and sun, and applies this knowledge to science and service which touches the lives of all Americans. Among its six major divisions are the National Environmental Satellite Data and Information Service (NESDIS) and the NWS. 1.1.1 National Environmental Satellite Data and Information Service (NESDIS) The National Environmental Satellite Data and Information Service (NESDIS) manages the U.S. civil operational remote-sensing satellite systems, as well as other global information for meteorology, oceanography, solid-earth geophysics, and solar-terrestrial sciences. NESDIS provides this data to NWS meteorologists and a wide range of other users for operational weather forecasting. 1.1.1.1 Satellite Analysis Branch (SAB) NESDIS' Satellite Analysis Branch (SAB) serves as the operational focal point for real-time imagery products and multi-disciplinary environmental analyses. The SAB’s primary mission is to support disaster mitigation and warning services for U.S. Federal agencies and the international community. Routine environmental analyses are provided to forecasters and other environmental users and used in the numerical models of the NWS. The SAB schedules and distributes real-time satellite imagery products from global geostationary and polar-orbiting satellites to environmental users. The SAB coordinates the satellite and other information for the NOAA Volcanic Hazards Alert program under an agreement with the FAA and works with the NWS as part of the Washington, D.C. Volcanic Ash Advisory Center (VAAC). 1.1.2 National Weather Service (NWS) The National Weather Service (NWS) provides weather data, forecasts and warnings for the United States, its territories, adjacent waters and ocean areas for the protection of life and property and the enhancement of the national economy. NWS data and products form a national information database and infrastructure that can be used by other government agencies, the private sector, the public and the global community. The following is a description of NWS offices associated with aviation weather. 1.1.2.1 National Centers for Environmental Prediction (NCEP) The National Centers for Environmental Prediction (NCEP) is where virtually all global meteorological data is collected and analyzed. NCEP then provides a wide variety of national and international weather guidance products to NWS field offices, government agencies, emergency managers, private sector meteorologists, and meteorological organizations and AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-1 ### Page 21 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) societies throughout the world. NCEP is a critical resource in national and global weather prediction and is the starting point for nearly all weather forecasts in the U. S. NCEP is comprised of nine distinct centers and the Office of the Director. Each center has its own specific mission. The following NCEP centers provide aviation weather products and services: 1.1.2.1.1 NCEP Central Operations (NCO) NCEP’s Central Operations (NCO) in Camp Springs, Maryland, sustains and executes the operational suite of the numerical analysis and forecast models and prepares NCEP products for dissemination. It also links all nine of the national centers together via computer and communications-related services. 1.1.2.1.2 Aviation Weather Center (AWC) The Aviation Weather Center (AWC), a Meteorological Watch Office (MWO) for the International Civil Aviation Organization (ICAO), is located in Kansas City, Missouri. The AWC issues the following products in support of FAA air traffic controllers and the National Airspace System (NAS): Airman’s Meteorological Information (AIRMETs), Significant Meteorological Information (SIGMETs), Convective SIGMETs, Area Forecasts (FAs), Significant Weather Prognostic Charts (low, middle, and high), Collaborative Convective Forecast Product (CCFP), National Convective Weather Forecast (NCWF), Current Icing Product (CIP), and Forecast Icing Potential (FIP). 1.1.2.1.3 Hydrometeorological Prediction Center (HPC) The Hydrometeorological Prediction Center (HPC) in Camp Springs, Maryland, provides analysis and forecast products specializing in quantitative precipitation forecasts to five days, weather forecast guidance to seven days, real-time weather model diagnostics discussions and surface pressure and frontal analyses. 1.1.2.1.4 Storm Prediction Center (SPC) The Storm Prediction Center (SPC) in Norman, Oklahoma, provides tornado and severe weather watches for the contiguous U. S. along with a suite of hazardous weather forecasts including the Alert Severe Weather Watch Bulletins and mesoscale guidance products 1.1.2.1.5 Tropical Prediction Center (TPC) The Tropical Prediction Center (TPC) in Miami, Florida, provides official NWS forecasts of the movement and strength of tropical weather systems and issues the appropriate watches and warnings for the contiguous U.S. and surrounding areas. It also issues a suite of marine products covering the tropical Atlantic, Caribbean, Gulf of Mexico, and tropical eastern Pacific. 1.1.2.2 Alaskan Aviation Weather Unit (AAWU) The Alaskan Aviation Weather Unit (AAWU), located in Anchorage, Alaska, is a MWO for the ICAO. The AAWU is responsible for the entire Anchorage Flight Information Region (FIR). They issue the following products for the airspace over Alaska and adjacent coastal waters: AIRMETs, SIGMETs, FAs, Graphic Area Forecasts, and Significant Weather Prognostic Charts (Low- and Mid-level – below flight level (FL) 250). The AAWU is also designated as the Anchorage Volcanic Ash Advisory Center (VAAC). The VAAC area of responsibility includes the Anchorage FIR and Far Eastern Russia and is responsible for the issuance of Volcanic Ash Advisories (FVs). AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-2 ### Page 22 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 1.1.2.3 Center Weather Service Unit (CWSU) Center Weather Service Units (CWSUs) are units of NWS meteorologists under contract with the FAA that are stationed at and support the FAA’s Air Route Traffic Control Centers (ARTCC). CWSUs provide timely weather consultation, forecasts, and advice to managers within ARTCCs and to other supported FAA facilities. This information is based on monitoring, analysis, and interpretation of real-time weather data at the ARTCC through the use of all available data sources including radar, satellite, Pilot Weather Reports (PIREPs), and various NWS products such as Terminal Aerodrome Forecasts (TAFs), FAs, and inflight advisories. Special emphasis is given to those weather conditions hazardous to aviation or which would impede the flow of air traffic within the NAS. Rerouting of aircraft around hazardous weather is based largely on forecasts provided by the CWSU meteorologist. They issue the following products in support of their respective ARTCC: Center Weather Advisories (CWA) and Meteorological Impact Statements (MIS). 1.1.2.4 Weather Forecast Office (WFO) A NWS Weather Forecast Office (WFO) is a multi-purpose, local weather forecast center that produces, among its suite of services, aviation-related products. In support of aviation, WFOs issue Terminal Aerodrome Forecasts (TAFs), Transcribed Weather En Route Broadcasts (TWEBs) forecasts, with some offices issuing Airport Weather Warnings, and Soaring Forecasts. WFO Honolulu is also designated as a Meteorological Watch Office (MWO) for ICAO. As a result of this unique designation, WFO Honolulu is the only WFO to issue the following text products: AIRMETs, SIGMETs, FAs, and Route Forecasts (ROFOR). WFO Honolulu serves as the Central Pacific Hurricane Center (CPHC). CPHC provides official NWS forecast of the movement and strength of tropical weather systems and issues the appropriate watches and warnings for the central Pacific including the State of Hawaii. WFO Honolulu also issues a suite of marine products covering a large portion of the Pacific Ocean. 1.1.2.5 NWS Office at the FAA Academy The mission of the National Weather Service (NWS) Office at the FAA Academy is to provide weather training for Federal Aviation Administration (FAA) Air Traffic Controllers, write reference materials, and administer NWS certification examinations for FAA Pilot Weather Briefers and Tower Visibility Observers. AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-3 ### Page 23 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 1.2 Federal Aviation Administration (FAA) The FAA, a part of the Department of Transportation (DOT), provides a safe, secure, and efficient aerospace system that contributes to national security and the promotion of U.S. aerospace safety. As the leading authority in the international aerospace community, the FAA is responsive to the dynamic nature of user needs, economic conditions, and environmental concerns. The FAA provides a wide range of services to the aviation community. The following is a description of those FAA facilities which are involved with aviation weather and pilot services. 1.2.1 Air Traffic Control System Command Center (ATCSCC) The Air Traffic Control System Command Center (ATCSCC) is located in Herndon, Virginia. ATCSCC has the mission of balancing air traffic demand with system capacity. This ensures maximum safety and efficiency for the NAS while minimizing delays. The ATCSCC utilizes the Traffic Management System, aircraft situation display, monitor alert, the follow-on functions, and direct contact with ARTCC and terminal radar approach control facility (TRACON) traffic management units to manage flow on a national level. Because weather is the most common reason for air traffic delays and re-routings, the ATCSCC is supported by Air Traffic Control System Command Center Weather Unit Specialists (ATCSCCWUS). These flight service specialists are responsible for the dissemination of meteorological information as it pertains to national air traffic flow management. 1.2.2 Air Route Traffic Control Center (ARTCC) An ARTCC is a facility established to provide air traffic control service to aircraft operating on Instrument Flight Rules (IFR) flight plans within controlled airspace and principally during the en route phase of flight. When equipment capabilities and controller workload permit, certain advisory/assistance services may be provided to Visual Flight Rules (VFR) aircraft. En route controllers become familiar with pertinent weather information and stay aware of current weather information needed to perform air traffic control duties. En route controllers advise pilots of hazardous weather that may impact operations within 150 NM of the controller’s assigned sector(s). 1.2.3 Air Traffic Control Tower (ATCT) and Terminal Radar Approach Control (TRACON) An ATCT is a terminal facility that uses air/ground communications, visual signaling, and other devices to provide ATC services to aircraft operating in the vicinity of an airport or on the movement area. It authorizes aircraft to land or take off at the airport controlled by the tower or to transit the Class D airspace area regardless of flight plan or weather conditions (IFR or VFR). A tower may also provide approach control services. TRACONs manage the airspace from 10 to 40 miles outside of selected airports and below 13,000 feet. They also coordinate aircraft spacing as they approach and depart these airports. Terminal controllers become familiar with pertinent weather information and stay aware of current weather information needed to perform air traffic control duties. Terminal controllers advise pilots of hazardous weather that may impact operations within 150 NM of the controller’s AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-4 ### Page 24 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) assigned sector or area of jurisdiction. ATCTs and TRACONs may opt to broadcast hazardous weather information alerts only when any part of the area described is within 50 NM of the airspace under the ATCT’s jurisdiction. The tower controllers are also properly certified and act as official weather observers as required. An Automatic Terminal Information Service (ATIS) is a continuous broadcast of recorded information in selected terminal areas. Its purpose is to improve controller effectiveness and to relieve frequency congestion by automating the repetitive transmission of non-controlled airport/terminal area and meteorological information. 1.2.4 Flight Service Station (FSS) / Automated Flight Service Station (AFSS) Flight Service Stations (FSSs) and Automated Flight Service Stations (AFSSs) provide pilot weather briefings, en route weather, receive and process IFR and VFR flight plans, relay ATC clearances, and issue Notices to Airmen (NOTAMs). They also provide assistance to lost aircraft and aircraft in emergency situations, and conduct VFR search and rescue services. AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-5 ### Page 25 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 1.3 Dissemination of Aviation Weather Products The ultimate users of aviation weather services are pilots and aircraft dispatchers. Maintenance personnel may use the service to keep informed of weather that could cause possible damage to unprotected aircraft. Pilots contribute to aviation weather services as well as use them. PIREPs help other pilots, dispatchers, briefers and forecasters as an observation of current conditions. In the interest of safety and in compliance with Title 14, Code of Federal Regulations, all pilots should get a complete weather briefing before each flight. The pilot is responsible for ensuring he/she has all the information needed to make a safe flight. 1.3.1 Weather Briefings Prior to every flight, pilots should gather all information vital to the nature of the flight. This includes an appropriate weather briefing obtained from a specialist at an FSS, AFSS, or via Direct User Access Terminal Service (DUATS). To provide an appropriate weather briefing, specialists need to know which of the three types of briefings is needed - a standard, abbreviated or outlook. Other helpful information is whether the flight will be conducted VFR or IFR, aircraft identification and type, departure point, estimated time of departure (ETD), flight altitude, route of flight, destination, and estimated time en route (ETE). This information is recorded in the flight plan system and a note is made regarding the type of weather briefing provided. If necessary, it can be referenced later to file or amend a flight plan. It is also used when an aircraft is overdue or is reported missing. 1.3.1.1 Standard Briefing A standard briefing provides a complete weather picture and is the most detailed of all briefings. This type of briefing should be obtained prior to the departure of any flight and should be used during flight planning. A standard briefing provides the following information in sequential order if it is applicable to the route of flight. 1. Adverse Conditions - This includes info rmation about adverse conditions that may influence a decision to cancel or alter the route of flight. Adverse conditions include significant weather such as thunderstorms, aircraft icing, turbulence, wind shear, reduced visibilities and other important items such as airport closings. 2. VFR Flight NOT RECOMMENDED (VNR) - If the weather for the route of flight is below VFR minimums, or if it is doubtful the flight could be made under VFR conditions due to the forecast weather, the briefer may state that VFR is not recommended. The pilot can then decide whether or not to continue the flight under VFR, but this advisory should be weighed carefully. 3. Synopsis - The synopsis is an overview of the larger weather picture. Fronts and major weather systems along or near the route of flight and weather which may affect the flight are provided. AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-6 ### Page 26 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4. Current Conditions - This portion of the briefing contains the current surface weather observations, pilot weather reports (PIREPs), satellite and radar data along the route of flight. If the departure time is more than 2 hours away, current conditions will not be included in the briefing. 5. En Route Forecast - The en route forecast is a summary of the weather forecast for the proposed route of flight. 6. Destination Forecast - The destination forecast is a summary of the expected weather for the destination airport at the estimated time of arrival (ETA). 7. Winds and Temperatures Aloft - Winds and temperatures aloft is a forecast of the winds at specific altitudes along the route of flight. However, the temperature information is provided only on request. 8. NOTAMs - This portion supplies Notice to Airmen (NOTAM) information pertinent to the route of flight which has not been published in the Notice to Airmen publication. Published NOTAM information is provided during the briefing only when requested. 9. ATC Delays - This is an advisory of any known air traffic control (ATC) delays that may affect the flight. 10. Other Information - At the end of the standard briefing, the specialist will provide the radio frequencies needed to open a flight plan and to contact En Route Flight Advisory Service (EFAS). Any additional information requested is also provided at this time. 1.3.1.2 Abbreviated Briefing An abbreviated briefing is a shortened version of the standard briefing. It should be requested when a departure has been delayed or when specific weather information is needed to update a previous standard briefing. When this is the case, the weather specialist needs to know the time and source of the previous briefing so the necessary weather information will not be omitted inadvertently. 1.3.1.3 Outlook Briefing An outlook briefing should be requested when a planned departure is 6 or more hours away. It provides initial forecast information that is limited in scope due to the timeframe of the planned flight. This type of briefing is a good source of flight planning information that can influence decisions regarding route of flight, altitude, and ultimately the “go, no-go” decision. A follow-up standard briefing prior to departure is advisable since an outlook briefing generally only contains information based on weather trends and existing weather in geographical areas at or near the departure airport. The FSS/AFSS’s purpose is to serve the aviation community. Pilots should not hesitate to ask questions and discuss factors they do not fully understand. The briefing should be considered complete only when the pilot has a clear picture of what weather to expect. Pilots should also make a final weather check immediately before departure if at all possible. 1.3.2 Direct Use Access Terminal Service (DUATS/DUAT) The Direct User Access Terminal Service, which is funded by the FAA, allows any pilot with a current medical certificate to access weather information and file a flight plan via computer. Two methods of access are available to connect with DUATS. The first is on the Internet AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-7 ### Page 27 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) through Computer Sciences Corporation (CSC) at http://www.duats.com or Data Transformation Corporation at http://www.duat.com. The second method requires a modem and a communications program supplied by a DUATS provider. To access the weather information and file a flight plan by this method, pilots use a toll free telephone number to connect the user’s computer directly to the DUATS computer. The current vendors of DUATS service and the associated phone numbers are listed in Chapter 7 of the Aeronautical Information Manual (AIM). 1.3.3 Aviation Digital Data Service (ADDS) The Aviation Digital Data Service (ADDS) provides the aviation community with text, digital and graphical forecasts, analyses, and observations of aviation-related weather variables. ADDS is a joint effort of NOAA Forecast Systems Laboratory (FSL), NCAR Research Applications Laboratory (RAL), and the AWC. 1.3.4 Telephone Information Briefing Service (TIBS) The Telephone Information Briefing Service (TIBS) is a service prepared and disseminated by selected Automated Flight Service Stations. It provides continuous telephone recordings of meteorological and aeronautical information. Specifically, TIBS provides area and route briefings, as well as airspace procedures and special announcements, if applicable. It is designed to be a preliminary briefing tool and is not intended to replace a standard briefing from a flight service specialist. The TIBS service is available 24 hours a day and is updated when conditions change, but it can only be accessed by a TOUCH-TONE phone. The phone numbers for the TIBS service are listed in the Airport/Facility Directory (A/FD). TIBS should also contain, but is not limited to: surface observations, TAFs, and winds/ temperatures aloft forecasts. Each AFSS provides at least four route and/or area briefings. As a minimum, area briefings encompass a 50 NM radius. Pilots have access to NOTAM data through: Area or route briefings, on separate channels that are designated specifically for NOTAMs, or by access to a briefer. Separate channels are designated for each route, area, local meteorological/aeronautical information, special event, airspace procedures, etc. The order and content of the TIBS recording is as follows: 1. Introduction. Includes the preparation time and the route and/or the area of coverage. The service area may be configured to meet the individual facility’s needs. 2. Adverse Conditions. A summary of Convective SIGMETs, SIGMETs, AIRMETs, Center Weather Advisories, Alert Severe Weather Watch Bulletins, and any other available information that may adversely affect flight in the route/area. 3. VNR Statement. Included when current or forecast conditions, surface or aloft, would make the flight under visual flight rules doubtful. 4. Synopsis. A brief statement describing t he type, location, and movement of weather systems and/or air masses that might affect the route or the area. This element may be combined with adverse conditions and/or the VNR element, in any order, when it will help to more clearly describe conditions. AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-8 ### Page 28 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5. Current Conditions. A summary of current weather conditions over the route/area. PIREPs are included on conditions reported aloft and a summary of observed radar echoes. Specific departure/destination observation may also be included. 6. Density Altitude. The statement “check density altitude” will be included for any weather reporting point with a field elevation of 2,000 feet MSL or above that meets certain temperature criteria. 7. En Route Forecast. A summary of appropriate forecast data provided in logical order, i.e., climb out, en route, and descent. 8. Winds Aloft. A summary of winds aloft forecast for the route/area as interpolate d from forecast data for the local and/or the adjacent reporting locations for levels through 12,000 feet. The broadcast should include the levels from 3,000 to 12,000 feet, but usually includes at least two forecast levels above the surface. 9. Request for PIREPs. When weather conditions within the area or along the route meet requirements for soliciting PIREPs, a request will be included in the recording. 10. NOTAM information that affects the route/area may be included as part of the briefing, on a separate channel, or obtained by direct contact with a pilot weather briefer. 11. Military Training Activity. A statement is included in the closing announcement to contact a briefer for information on military training activity. 12. Closing Announcement. TIBS services may be reduced during the hours of 1800-0600 local time only. Resumption of full broadcast service is adjusted seasonally to coincide with daylight hours. During the period of reduced broadcast, a recorded statement may indicate when the broadcast will be resumed and to contact Flight Service for weather briefing and other services. For those pilots already in flight and needing weather information and assistance, the following services are provided by flight service stations. They can be accessed over the proper radio frequencies printed in flight information publications. 1.3.5 Hazardous Inflight Weather Advisory Service (HIWAS) HIWAS is a national program for broadcasting hazardous weather information continuously over selected navigational aids (NAVAIDs). The broadcasts include advisories such as AIRMETs, SIGMETS, convective SIGMETs, and urgent PIREPs. These broadcasts are only a summary of the information, and pilots should contact an FSS/AFSS or En Route Flight Advisory Service (EFAS) for detailed information. The HIWAS broadcast area is defined as the area within 150 NM of HIWAS outlets. HIWAS broadcasts are not interrupted or delayed except for emergency situations, when an aircraft requires immediate attention, or for reasonable use of the voice override capability on specific HIWAS outlets in order to use the limited Remote Communications Outlet (RCO) to maintain en route communications. The service is provided 24-hours a day. An announcement is made for no hazardous weather advisories. AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-9 ### Page 29 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Hazardous weather information is recorded if it is occurring within the HIWAS broadcast area. The broadcast includes the following elements: 1. A statement of introduction including the appropriate area(s) and a recording time. 2. A summary of Convective SIGMETs, SIGMETs, AIRMET s, Urgent PIREPs, Aviation Watch Notification Messages, Center Weather Advisories, and any other weather such as isolated thunderstorms that are rapidly developing and increasing in intensity, or low ceilings and visibilities that are becoming widespread which are considered significant and are not included in a current hazardous weather advisory. 3. A request for PIREPs, if applicable. 4. A recommendation to contact AFSS/FSS/FLIGHT WATCH for additional details concerning hazardous weather. Once the HIWAS broadcast is updated, an announcement will be made once on all communications/NAVAID frequencies except emergency, EFAS, and navigational frequencies already dedicated to continuous broadcast services. In the event a HIWAS broadcast area is out of service, an announcement is made on all communications/NAVAID frequencies except on emergency, EFAS, and navigational frequencies already dedicated to continuous broadcast services. 1.3.6 En Route Flight Advisory Service (EFAS) The purpose of EFAS, radio call “FLIGHT WATCH” (FW), is to provide en route aircraft with timely and pertinent weather data tailored to a specific altitude and route using the most current available sources of aviation meteorological information. EFAS specialists tailor en route flight advisories to the phase of flight that begins after climb out and ends with descent to land. Current weather and terminal forecast at the airport of first intended landing and/or the alternate airport is provided on request. When conditions dictate, EFAS specialists provide information on weather for alternate routes and/or altitudes to assist the pilot in the avoidance of hazardous flight conditions. The pilot is advised to contact the adjacent flight watch facility when adverse weather conditions along the intended route extend beyond the Flight Watch Area (FWA). EFAS is NOT used for routine in-flight services; e.g., flight plan filing, position reporting, or full route (pre-flight) briefings. If a request for information is received that is not within the scope of EFAS, the pilot is advised of the appropriate AFSS/FSS to contact. EFAS specialists suggest route or destination changes to avoid areas of weather that in the judgment of the specialists constitutes a threat to safe flight. EFAS is provided on 122.0 MHz to aircraft below FL180. An assigned discrete frequency is used to provide EFAS to aircraft at FL180 and above. This frequency can also be used for communications with aircraft below FL180 when communication coverage permits. Aircraft AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-10 ### Page 30 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) operating at FL 180 or above that contact FW on frequency 122.0 MHz are advised to change to the discrete frequency for EFAS. 1.3.7 Automatic Dependent Surveillance – Broadcast (ADS-B) Automatic Dependent Surveillance–Broadcast (ADS-B ) is a surveillance system combining the advanced technologies of satellite positioning, aircraft avionics, and ground based transceivers. ADS-B equipped aircraft automatically broadcast their identification, current position, altitude, and velocity information approximately once per second. This continuous broadcast of flight data, improves aircraft position accuracy beyond the capabilities of current NAS radar/transponder based surveillance systems. In the United States, two different data links have been adopted for use with ADS −B: 1090 MHz Extended Squitter (1090ES) and the 978 MHz, Universal Access Transceiver (UAT). The 1090ES link is intended for aircraft that primarily operate at FL240 and above, whereas the UAT link is intended for use by aircraft that primar ily operate at lower altitudes. From a pilot’s standpoint, the two links operate similarly and support ADS −B and Traffic Information Services- Broadcast (TIS-B). The UAT link will provide additional weather and other aeronautical information through the Flight Information Service − Broadcast (FIS-B). 1.3.7.1 Flight Information Service – Broadcast (FIS-B) FIS-B provides certain aviation weather and other aeronautical information to aircraft equipped with an appropriate cockpit display. Reception of FIS-B services can be expected within a ground station coverage volume when line-of-sight geometry is maintained between the aircraft and ground station. NAS-wide service availability is targeted for 2013 and is currently available within certain regions. 1.3.7.1.1 FIS-B Products FIS-B provides the following textual and graphi cal aviation weather and aeronautical products free-of-charge. A detailed description of these products can be found within this Advisory Circular and the Aeronautical Information Manual (AIM). Textual • Aviation Routine Weather Reports (METARs) and Aviation Selected Special Weather Reports (SPECIs) • Pilot Weather Reports (PIREPS) • Terminal Aerodrome Forecasts (TAFs) and their amendments • Winds and Temperatures Aloft Graphical • WSR-88D (NEXRAD) Weather Radar CONUS and regional-scale composite reflectivity mosaic products Text/Graphical Overlay • Notice to Airmen (NOTAM) Distant and Flight Data Center • Airmen’s Meteorological Information (AIRMET) • Significant Meteorological Information (SIGMET) • Convective SIGMET • Status of Special Use Airspace (SUA); • Temporary Flight Restriction (TFR) NOTAMS AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-11 ### Page 31 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Section 1: Aviation Weather Service Program Page 1-12 Subject to FAA approval, additional products may be offered by the service provider in the future which may incur a usage fee. 1.3.7.1.2 Operational Use of FIS-B Products FIS-B products are intended to enhance the user’s situational awareness and enable more efficient use of ATC/FSS/AOCC services. The in formation provided by FIS-B is advisory in nature and should not be used in lieu of individual pre-flight, in-flight, weather, or flight planning briefings provided by ATC/FSS/AOCC services. Specific guidance on the operational use of Flight Information Services can be found in Chapter 7, Safety of Flight of the AIM. Guidance concerning the content, format, and symbology of individual FIS-B products should be obtained from the manufacturer of the avionics equipment used to receive and display them. ### Page 32 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 2 AVIATION WEATHER PRODUCT CLASSIFICATION AND POLICY The demand for new and improved aviation weather products continues to grow and, with new products introduced to meet the demand, some confusion has resulted in the aviation community regarding the relationship between regulatory requirements and the new weather products. This section will clarify that relationship by providing: • classification of the weather products and policy guidance in their use, • descriptions of the types of aviation weather information, and • categorization of the sources of aviation weather information. 2.1 Classification of Aviation Weather Products The FAA has developed two classifications of aviation weather products: primary weather products, and supplementary weather products. The classifications are meant to eliminate confusion by differentiating between weather products that may be used to meet regulatory requirements and other weather products that may only be used to improve situational awareness. All flight-related, aviation weather decisions must be based on the primary weather products. Supplementary weather products augment the primary products by providing additional weather information, but may not be used as stand-alone products to meet aviation weather regulatory requirements or without the relevant primary products. When discrepancies exist between primary and supplementary products pertaining to the same weather phenomena, pilots must base flight-related decisions on the primary weather product. Furthermore, multiple primary products may be necessary to meet all aviation weather regulatory requirements. Aviation weather products produced by the federal government (NWS) are primary products unless designated as a supplementary product by the FAA. In addition, the FAA may choose to restrict certain weather products to specific types of usage or classes of user. Any limitations imposed by the FAA on the use of a product will appear in the product label. 2.1.1 Primary Weather Product Classification A primary weather product is an aviation weather product that meets all of the regulatory requirements and safety needs for use in making weather-related flight decisions. Note: Sections 3 through 8 of this Advisory Circular are considered Primary Weather Products. 2.1.2 Supplementary Weather Product Classification A supplementary weather product is an aviation weather product that may be used for enhanced situational awareness. A supplementary weather product must only be used in conjunction with one or more primary weather products. In addition, the FAA may further restrict the use of the supplementary weather products through limitations described in the product label. AC 00-45F, CHG 2 Section 2: Aviation Weather Product Classification and Policy Page 2-1 ### Page 33 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Note: Section 9 of this Advisory Circular contains information on Supplementary Weather Products. 2.2 Types of Aviation Weather Information The FAA has identified the following three distinct types of weather information that may be needed to conduct aircraft operations: observations, analyses, and forecasts. 2.2.1 Observations Observations are raw weather data collected by some type of sensor(s). The observations can either be in situ (e.g. surface or airborne) or remote (e.g. weather radar, satellite, profiler, and lightning). 2.2.2 Analysis Analyses of weather information are an enhanced depiction and/or interpretation of observed weather data. 2.2.3 Forecasts Forecasts are the predictions of the development and/or movement of weather phenomena based on meteorological observations and various mathematical models. In-flight weather advisories, including Significant Meteorological Information (SIGMET), Convective SIGMETs, Airman’s Meteorological Information (AIRMET), Center Weather Advisories (CWA), and Meteorological Impact Statements (MIS), are considered forecast weather information products. 2.3 Categorizing Aviation Weather Sources The regulations pertaining to aviation weather reflect that, historically, the federal government was the only source of aviation weather information. That is, the FAA and NWS, or its predecessor organizations, were solely responsible for the collection and dissemination of weather data, including forecasts. Thus, the term “approved source(s)” referred exclusively to the federal government. The federal government is no longer the only source of weather information, due to the growing sophistication of aviation operations and scientific and technological advances. Since all three types of weather information defined in paragraph 2.3 are not available from all sources of aviation weather information, the FAA has categorized the sources as follows: federal government, Enhanced Weather Information System (EWINS), and commercial weather information providers. 2.3.1 Federal Government The FAA and NWS collect weather observations. The NWS analyzes the observations, and produces forecasts, including in-flight aviation weather advisories (e.g., SIGMETs). The FAA and NWS disseminate meteorological observations, analyses, and forecast products through a variety of systems. The federal government is the only approval authority for sources of weather observations (e.g., contract towers and airport operators). AC 00-45F, CHG 2 Section 2: Aviation Weather Product Classification and Policy Page 2-2 ### Page 34 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Section 2: Aviation Weather Product Classification and Policy Page 2-3 Commercial weather information providers contracted by the FAA to provide weather observations (e.g., contract towers) are included in the federal government category of approved sources by virtue of maintaining required technical and quality assurance standards under FAA and NWS oversight. 2.3.2 Enhanced Weather Information System (EWINS) EWINS is an FAA-approved proprietary system for tracking, evaluating, reporting, and forecasting the presence or absence of adverse weather phenomena. EWINS is authorized to produce flight movement forecasts, adverse weather phenomena forecasts, and other meteorological advisories. To receive FAA approval, EWINS-approved source must have sufficient procedures, personnel, and communications and data processing equipment to effectively obtain, analyze, and disseminate aeronautical weather data. For a full explanation of the requirements for EWINS approval, see the Air Transportation Operations Inspector’s Handbook, Order 8400.10, volume 3, chapter 7, section 5. An EWINS-approved source may produce weather analyses and forecasts based on meteorological observations provided by the federal government. Approval to use EWINS weather products is issued on a case by case basis and is currently only applicable to FAR part 121 and 135 certificate holders, who may either act as their own EWINS or contract those services from a separate entity. For these approved users, the weather analyses and forecasts produced by their approved EWINS are considered primary weather products as defined in paragraph 2.2.1, Primary Weather Products. 2.3.3 Commercial Weather Information Providers Commercial weather providers are a major source of weather products for the aviation community. In general, they produce proprietary weather products based on NWS products with formatting and layout modifications but no material changes to the weather information itself. This is also referred to as “repackaging.” Commercial providers may also produce forecasts, analyses, and other proprietary weather products and substantially alter the information contained in NWS-produced products. Hence, operators and pilots contemplating using such services should request and/or review an appropriate description of services and provider disclosure. This should include, but is not limited to, • the type of weather product (e.g., current weather or forecast weather), • the currency of the product (i.e., product issue and valid times), and • the relevance of the product. Pilots and operators should be cautious when using unfamiliar products, or products not supported by FAA/NWS technical specifications. Commercially-available proprietary weather products that substantially alter NWS-produced weather products, or information, may only be approved for use by part 121 or part 135 operators or fractional ownership programs if the commercial provider is EWINS-qualified (see paragraph 2.4.2, above). Government products that are only repackaged and not altered, or products produced by EWINS-approved source, are considered primary weather products as defined in paragraph 2.2.1, Primary Weather Products. ### Page 35 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3 OBSERVED TEXT PRODUCTS 3.1 Aviation Routine Weather Reports (METAR) and Aviation Selected Special Weather Reports (SPECI) Surface weather observations are fundamental to all meteorological services. Observations are the basic information upon which forecasts and warnings are made in support of a wide range of weather sensitive activities within the public and private sectors, including aviation. Although the METAR/SPECI code is used worldwide, each country is allowed to make modifications or exceptions to the code for use in their particular country. This section will focus on the U.S. modifications and exceptions. METAR/SPECIs are available online at: http://adds.aviationweather.gov/metars/ 3.1.1 Aviation Routine Weather Report (METAR) Aviation Routine Weather Report (METAR) is the primary observation code used in the U. S. to satisfy World Meteorological Organization (WMO) and International Civil Aviation Organization (ICAO) requirements for reporting surface meteorological data. A METAR report includes the airport identifier, time of observation, wind, visibility, runway visual range, present weather phenomena, sky conditions, temperature, dew point, and altimeter setting. Excluding the airport identifier and the time of observation, this information is collectively referred to as “the body of the report.” As an addition, coded and/or plain language information elaborating on data in “the body of the report” may be appended to the end of the METAR in a section coded as “Remarks.” The contents of the “Remarks” section vary with the type of reporting station. The METAR may be abridged at some designated stations only including a few of the mentioned elements. 3.1.2 Aviation Selected Special Weather Report (SPECI) An Aviation Selected Special Weather Report (SPECI) is an unscheduled report taken when any of the criteria given in Table 3-1 are observed during the interim period between the hourly reports. SPECI contains all data elements found in a METAR plus additional plain language information which elaborates on data in the body of the report. All SPECIs are made as soon as possible after the relevant criteria are observed. Whenever SPECI criteria are met at the time of the routine METAR, a METAR is issued. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-1 ### Page 36 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-1. SPECI Criteria 1 Wind Shift Wind direction changes by 45 degrees or more in less than 15 minutes and the wind speed is 10 knots or more throughout the wind shift. 2 Visibility Surface visibility as reported in the body of the report decreases to less than, or if below, increases to equal or exceed: a. 3 miles b. 2 miles c. 1 mile d. The lowest standard instrument approa ch procedure minimum as published in the National Ocean Service (NOS) U.S Instrument Procedures. If none published use ½ mile. 3 Runway Visual Range (RVR) The highest value from the designated RVR runway decreases to less than, or if below, increases to equal or exceed 2,400 feet during the preceding 10 minutes. U.S. military stations may not report a SPECI based on RVR. 4 Tornado, Funnel Cloud, or Waterspout a. is observed. b. disappears from sight, or ends. 5 Thunderstorm a. begins (a SPECI is not required to report the beginning of a new thunderstorm if one is currently reported). b. ends. 6 Precipitation a. hail begins or ends. b. freezing precipitation begins , ends, or changes intensity. c. ice pellets begin, end, or change intensity 7 Squalls When they occur 8 Ceiling The ceiling (rounded off to reportable values) forms or dissipates below, decreases to less than, or if below, increases to equal or exceed: a. 3,000 feet. b. 1,500 feet c. 1,000 feet d. 500 feet e. The lowest standard instrument approa ch procedure minimum as published in the National Ocean Service (NOS) U.S Instrument Procedures. If none published, use 200 feet. 9 Sky Condition A layer of clouds or obscurations aloft is present below 1,000 feet and no layer aloft was reported below 1,000 feet in the preceding METAR or SPECI. 10 Volcanic Eruption When an eruption is first noted 11 Aircraft Mishap Upon notification of an aircraft mishap, unless there has been an intervening observation 12 Miscellaneous Any other meteorological situation designated by the responsible agency of which, in the opinion of the observer, is critical. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-2 ### Page 37 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3 Format Figure 3-1. METAR/SPECI Coding Format A METAR/SPECI (Figure 3-1) has two major sections: the Body (consisting of a maximum of 11 groups) and the Remarks (consisting of 2 categories). Together, the body and remarks make up the complete METAR/SPECI. When an element does not occur, or cannot be observed, the corresponding group is omitted from that particular report. 3.1.3.1 Type of Report METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The type of report, METAR or SPECI precedes the body of all reports. 3.1.3.2 Station Identifier METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The station identifier, in ICAO format, is included in all reports to identify the station to which the coded report applies. The ICAO airport code is a four-letter alphanumeric code designating each airport around the world. The ICAO codes are used for flight planning by air traffic controllers and airline operation departments. These codes are not the same as the International Air Transport Association (IATA) codes encountered by the general public used for reservations, baggage handling and in airline timetables. ICAO codes are also used to identify weather stations located on- or offairport. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-3 ### Page 38 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Unlike the IATA codes, the ICAO codes have a regional structure. For example, the first letter is allocated by continent (Figure 3-2), the second is a country within the continent; the remaining two are used to identify each airport. Figure 3-2. ICAO Continent codes In the contiguous U. S., ICAO station identifiers are coded K followed by the three-letter IATA identifier. For example, the Seattle, Washington (IATA identifier SEA) becomes the ICAO identifier KSEA. ICAO station identifiers in Alaska, Hawaii, and Guam begin with the continent code P, followed by the proper country code (A, H, and G respectively), and the two-letter airport identifier. Examples: PANC Anchorage, AK PAOM Nome, AK PHNL Honolulu, HI PHKO Keahole Point, HI PGUM Agana, Guam PGUA Anderson AFB, Guam Canadian station identifiers begin with C, followed by the country code, and the two-letter airport identifier. Examples: AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-4 ### Page 39 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) CYYZ Toronto, Canada CYYC Calgary Canada CYQB Quebec, Canada CYXU London, Canada CZUM Churchill Falls, Canada Mexican and western Caribbean station identifiers begin with M, followed by the proper country code and two-letter airport identifier. Examples: MMMX Mexico City, Mexico MUGM Guantanamo Bay, Cuba MDSD Santo Domingo, Dominican Republic MYNN Nassau, Bahamas Eastern Caribbean station identifiers begin with T, followed by the proper country code, and airport identifier. Examples: TJSJ San Juan, Puerto Rico TIST Saint Thomas, Virgin Islands For a list of Alaskan, Hawaiian, Canadian, Mexican, Pacific, and Caribbean ICAO identifiers see FAA Order 7350.7. For a complete worldwide listing, see ICAO Document 7910, “Location Indicators.” Both are available on-line. 3.1.3.3 Date and Time of Report METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The date and time is coded in all reports as follows: the day of the month is the first two digits (01) followed by the hour (19), and the minutes (55). The coded time of observations is the actual time of the report or when the criteria for a SPECI is met or noted. If the report is a correction to a previously disseminated report, the time of the corrected report is the same time used in the report being corrected. The date and time group always ends with a Z indicating Zulu time (or UTC). For example, METAR KOKC 011955Z would be disseminated as the 2000 hour scheduled report for station KOKC taken on the 1st of the month at 1955 UTC. 3.1.3.4 Report Modifier (As Required) METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The report modifier, AUTO, identifies the METAR/SPECI as a fully automated report with no human intervention or oversight. In the event of a corrected METAR or SPECI, the report modifier, COR, is substituted for AUTO. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-5 ### Page 40 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.5 Wind Group METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Wind is the horizontal motion of air past a given point. It is measured in terms of velocity, which is a vector that includes direction and speed. It indicates the direction the wind is coming FROM. In the wind group, the wind direction is coded as the first three digits (220) and is determined by averaging the recorded wind direction over a 2-minute period. It is coded in tens of degrees relative to true north using three figures. Directions less than 100 degrees are preceded with a 0. For example, a wind direction of 900 is coded as 090. Immediately following the wind direction is the wind speed coded in two or three digits (15). Wind speed is determined by averaging the speed over a 2-minute period and is coded in whole knots using the units, tens digits and, when required, the hundreds digit. When wind speeds are less than 10 knots, a leading zero is used to maintain at least a two digit wind code. For example, a wind speed of 8 knots will be coded 08KT. The wind group is always coded with a KT to indicate wind speeds are reported in knots. Other countries may use kilometers per hour (KPH) or meters per second (MPS) instead of knots. Examples: 05008KT Wind 50 degrees at 8 knots 15014KT Wind 150 degrees at 14 knots 340112KT Wind 340 degrees at 112 knots 3.1.3.5.1 Wind Gust Wind speed data for the most recent 10 minutes is examined to evaluate the occurrence of gusts. Gusts are defined as rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. The coded speed of the gust is the maximum instantaneous wind speed. Wind gusts are coded in two or three digits immediately following the wind speed. Wind gusts are coded in whole knots using the units, tens, and, if required, the hundreds digit. For example, a wind out of the west at 20 knots with gusts to 35 knots would be coded 27020G35KT. 3.1.3.5.2 Variable Wind Direction (speed 6 knots or less) Wind direction may be considered variable when, during the previous 2-minute evaluation period, the wind speed was 6 knots or less. In this case, the wind may be coded as VRB in place of the 3-digit wind direction. For example, if the wind speed was recorded as 3 knots, it would be coded VRB03KT. 3.1.3.5.3 Variable Wind Direction (speed greater than 6 knots) Wind direction may also be considered variable when, during the 2-minute evaluation period, it varies by 60 degrees or more and the speed is greater than 6 knots. In this case a variable wind direction group immediately follows the wind group. The directional variability is coded in a clockwise direction and consists of the extremes of the wind directions separated by a V. For AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-6 ### Page 41 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) example, if the wind is variable from 180º to 240º at 10 knots, it would be coded 21010KT 180V240. 3.1.3.5.4 Calm Wind When no motion of air is detected, the wind is reported as calm. A calm wind is coded as 00000KT. 3.1.3.6 Visibility Group METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Visibility is a measure of the opacity of the atmosphere. Prevailing visibility is the reported visibility considered representative of recorded visibility conditions at the station during the time of observation. It is the greatest distance that can be seen throughout at least half of the horizon circle, not necessarily continuous. Surface visibility is the prevailing visibility from the surface at manual stations or the visibility derived from sensors at automated stations. The visibility group is coded as the surface visibility in statute miles. A space is coded between whole numbers and fractions of reportable visibility values. The visibility group ends with SM to indicate that the visibility is in statute miles. For example, a visibility of one and a half statute miles is coded 1 1/2SM. Other countries may use meters (no code). Automated stations use an M to indicate “less than.” For example, M1/4SM means a visibility of less than one-quarter statute mile. 3.1.3.7 Runway Visual Range (RVR) Group METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The runway visual range (RVR) is an instrument-derived value representing the horizontal distance a pilot may see down the runway. RVR is reported whenever the station has RVR equipment and prevailing visibility is 1 statute mile or less and/or the RVR for the designated instrument runway is 6,000 feet or less. Otherwise the RVR group is omitted. Runway visual range is coded in the following format: the initial R is code for runway and is followed by the runway number. When more than one runway is defined with the same runway number a directional letter is coded on the end of the runway number. Next is a solidus /; followed by the visual range in feet and then FT completes the RVR report. For example, an RVR value for Runway 01L of 800 feet would be coded R01L/0800FT. Other countries may use meters. RVR values are coded in increments of 100 feet up to 1,000 feet, increments of 200 feet from 1,000 feet to 3,000 feet, and increments of 500 feet from 3,000 feet to 6,000 feet. Manual RVR AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-7 ### Page 42 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) is not reported below 600 feet. At automated stations, RVR may be reported for up to four designated runways. When the RVR varies by more than one reportable value, the lowest and highest values will be shown with V between them indicating variable conditions. For example, the 10-minute RVR for runway 01L varying between 600 and 1,000 feet would be coded R01L/0600V1000FT. If RVR is less than its lowest reportable value, the visual range group is preceded by M. For example, an RVR for runway 01L of less than 600 feet is coded R01L/M0600FT. If RVR is greater than its highest reportable value, the visual range group is preceded by a P. For example, an RVR for runway 27 of greater than 6,000 feet will be coded R27/P6000FT. 3.1.3.8 Present Weather Group METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Present weather includes precipitation, obscurations, and other weather phenomena. The appropriate notations found in Table 3-2 are used to code present weather. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-8 ### Page 43 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-2. METAR/SPECI Notations for Reporting Present Weather1 **QUALIFIER WEATHER PHENOMENA** **INTENSITY OR** **PROXIMITY** **DESCRIPTOR PRECIPITATION OBSCURATION OTHER 1 2 3 4 5** - Light MI Shallow DZ Drizzle BR Mist PO Dust/Sand whirls Moderate2 PR Partial RA Rain FG Fog SQ Squalls + Heavy BC Patches SN Snow FU Smoke FC Funnel Cloud, Tornado, or Waterspout4 VC In the Vicinity3 DR Low Drifting SG Snow Grains VA Volcanic Ash SS Sandstorm BL Blowing IC Ice Crystals (Diamond Dust) DU Widespread Dust DS Duststorm SH Shower(s) PL Ice Pellets SA Sand TS Thunderstorms GR Hail HZ Haze FZ Freezing GS Small Hail and/or Snow Pellets PY Spray UP Unknown Precipitation 1. The weather groups are construct ed by considering columns 1 to 5 in the table above in sequence, i.e., intensity followed by description, followed by weather phenomena, e.g., heavy rain shower(s) is coded as +SHRA. 2. To denote moderate intensity no entry or symbol is used. 3. See text for vicinity definitions. 4. Tornadoes and waterspouts are coded as +FC. Separate groups are used for each type of present weather. Each group is separated from the other by a space. METAR/SPECI reports contain no more than three present weather groups. When more than one type of present weather is reported at the same time, present weather is reported in the following order: • Tornadic activity – Tornado, Funnel Cloud, or Waterspout. • Thunderstorm(s) with and without associated precipitation. • Present weather in order of decreasing dominance, i.e., the most dominant type is reported first. • Left-to-right in Table 3-2 (Columns 1 through 5). AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-9 ### Page 44 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Qualifiers may be used in various combinations to describe weather phenomena. Present weather qualifiers fall into two categories: intensity (Section 3.1.3.8.1) or proximity (Section 3.1.3.8.2) and descriptors (Section 3.1.3.8.3). 3.1.3.8.1 Intensity Qualifier The intensity qualifiers are light, moderate, and heavy. They are coded with precipitation types except ice crystals (IC) and hail (GR or GS) including those associated with a thunderstorm (TS) and those of a showery nature (SH). Tornadoes and waterspouts are coded as heavy (+FC). No intensity is ascribed to the obscurations of blowing dust (BLDU), blowing sand (BLSA), and blowing snow (BLSN). Only moderate or heavy intensity is ascribed to sandstorm (SS) and duststorm (DS). When more than one form of precipitation is occurring at a time or precipitation is occurring with an obscuration, the reported intensities are not cumulative. The reported intensity will not be greater than the intensity for each form of precipitation. 3.1.3.8.2 Proximity Qualifier Weather phenomena occurring beyond the point of observation (between 5 and 10 statute miles) are coded as in the vicinity (VC). VC can be coded in combination with thunderstorm (TS), fog (FG), shower(s) (SH), well-developed dust/sand whirls (PO), blowing dust (BLDU), blowing sand (BLSA), blowing snow (BLSN), sandstorm (SS), and duststorm (DS). Intensity qualifiers are not coded in conjunction with VC. For example, VCFG can be decoded as meaning some form of fog is between 5 and 10 statute miles of the point of observation. If VCSH is coded, showers are occurring between 5 and 10 statute miles of the point of observation. Weather phenomena occurring at the point of observation (at the station) or in the vicinity of the point of observation are coded in the body of the report. Weather phenomena observed beyond 10SM from the point of observation (at the station) is not coded in the body but may be coded in the remarks section (Section 3.1.3.12). 3.1.3.8.3 Descriptor Qualifier Descriptors are qualifiers which further amplify weather phenomena and are used in conjunction with some types of precipitation and obscurations. The descriptor qualifiers are: shallow (MI), partial (PR), patches (BC), low drifting (DR), blowing (BL), shower(s) (SH), thunderstorm (TS), and freezing (FZ). Only one descriptor is coded for each weather phenomena group, e.g., FZDZ. The descriptors shallow (MI), partial (PR), and patches (BC) are only coded with FG, e.g., MIFG. Mist (BR) is not coded with any descriptor. The descriptors low drifting (DR) and blowing (BL) will only be coded with dust (DU), sand (SA), and snow (SN), e.g., BLSN or DRSN. DR is coded with DU, SA, or SN for raised particles drifting less than six feet above the ground. When blowing snow is observed with snow falling from clouds, both phenomena are reported, e.g., SN BLSN. If blowing snow is occurring and the observer cannot determine whether or not snow is also falling, then BLSN is reported. Spray (PY) is coded only with blowing (BL). AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-10 ### Page 45 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) The descriptor for showery-type precipitation (SH) is coded only with one or more of the precipitation qualifiers for rain (RA), snow (SN), ice pellets (PL), small hail (GS), or large hail (GR). The SH descriptor indicates showery-type precipitation. When any type of precipitation is coded with VC, the intensity and type of precipitation is not coded. The descriptor for thunderstorm (TS) may be coded by itself when the thunderstorm is without associated precipitation. A thunderstorm may also be coded with the precipitation types of rain (RA), snow (SN), ice pellets (PL), small hail and/or snow pellets (GS), or hail (GR). For example, a thunderstorm with snow and small hail and/or snow pellets would be coded as TSSNGS. TS are not coded with SH. The descriptor freezing (FZ) is only coded in combination with fog (FG), drizzle (DZ), or rain (RA), e.g., FZRA. FZ is not coded with SH. 3.1.3.8.4 Precipitation Precipitation is any of the forms of water particles, whether liquid or solid, that falls from the atmosphere and reaches the ground. The precipitation types are: drizzle (DZ), rain (RA), snow (SN), snow grains (SG), ice crystals (IC), ice pellets (IP), hail (GR), small hail and/or snow pellets (GS), and unknown precipitation (UP). UP is reported if an automated station detects the occurrence of precipitation but the precipitation sensor cannot recognize the type. Up to three types of precipitation may be coded in a single present weather group. They are coded in order of decreasing dominance based on intensity. 3.1.3.8.5 Obscuration Obscurations are any phenomenon in the atmosphere, other than precipitation, reducing the horizontal visibility. The obscuration types are: mist (BR), fog (FG), smoke (FU), volcanic ash (VC), widespread dust (DU), sand (SA), haze (HZ), and spray (PY). Spray (PY) is coded only as BLPY. With the exception of volcanic ash, low drifting dust, low drifting sand, low drifting snow, shallow fog, partial fog, and patches (of) fog, an obscuration is coded in the body of the report if the surface visibility is less than 7 miles or considered operationally significant. Volcanic ash is always reported when observed. 3.1.3.8.6 Other Weather Phenomena Other weather phenomena types include: well-developed dust/sand whirls (PO), sand storms (SS), dust storms (DS), squalls (SQ), funnel clouds (FC), and tornados and waterspouts (+FC). Examples: -DZ L i g h t drizzle -RASN Light rain and snow SN BR (Moderate) snow, mist -FZRA FG Light freezing rain, fog SHRA (Moderate) rain shower VCBLSA Blowing sand in the vicinity -RASN FG HZ Light rain and snow, fog, haze TS Thunderstorm (without precipitation) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-11 ### Page 46 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) +TSRA Thunderstorm, heavy rain +FC TSRAGR BR Tornado, thunderstorm, (moderate) rain, hail, mist 3.1.3.9 Sky Condition Group METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Sky condition is a description of the appearance of the sky. It is coded as: sky condition, vertical visibility, or clear skies. The sky condition group is based on the amount of sky cover (the first three letters) followed by the height of the base of the sky cover (final three digits). No space is between the amount of sky cover and the height of the layer. The height of the layer is recorded in feet Above Ground Level (AGL). Sky condition is coded in ascending order and ends at the first overcast layer. At mountain stations, if the layer is below station level, the height of the layer will be coded as ///. Vertical visibility is coded as VV followed by the vertical visibility into the indefinite ceiling. No space is between the group identifier and the vertical visibility. Figure 3-3 illustrates the effect of an obscuration on the vision from a descending aircraft. Figure 3-3. Obscuration Effects on Slant Range Visibility The ceiling is 500 feet in both examples, but the indefinite ceiling example (bottom) produces a more adverse impact to landing aircraft. This is because an obscuration (e.g., fog, blowing dust, snow, etc.) limits runway AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-12 ### Page 47 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) acquisition due to reduced slant range visibility. This pilot would be able to see the ground but not the runway. If the pilot was at approach minimums, the approach could not be continued and a missed approach must be executed. Clear skies are coded in the format, SKC or CLR. When SKC is used, an observer indicates no layers are present; and CLR is used by automated stations to indicate no layers are detected at or below 12,000 feet. Each coded layer is separated from the others by a space. Each layer reported is coded by using the appropriate reportable contraction seen in Table 3-3. A report of clear skies (SKC or CLR) is a complete layer report within itself. The abbreviations FEW, SCT, BKN, and OVC will be followed, without a space, by the height of the layer. Table 3-3. METAR/SPECI Contractions for Sky Cover Reportable Contraction Meaning Summation Amount of Layer VV Vertical Visibility 8/8 SKC or CLR1 Clear 0 FEW2 Few 1/8 – 2/8 SCT Scattered 3/8 – 4/8 BKN Broken 5/8 – 7/8 OVC Overcast 8/8 1. The abbreviation CLR will be used at automated stations when no layers at or below 12,000 feet are reported; the abbreviation SKC will be used at manual stations when no layers are reported. 2. Any layer amount less than 1/8 is reported as FEW. The height is coded in hundreds of feet above the surface using three digits in accordance with Table 3-4. Table 3-4. METAR/SPECI Increments of Reportable Values of Sky Cover Height Range of Height Values (feet) Reportable Increment (feet) Less than or equal to 5,000 To nearest 100 5,001 to 10,000 To nearest 500 Greater than 10,000 To nearest 1,000 The ceiling is the lowest layer aloft reported as broken or overcast. If the sky is totally obscured with ground based clouds, the vertical visibility is the ceiling. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-13 ### Page 48 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 3-4. METAR/SPECI Sky Condition Coding Clouds at 1,200 feet obscure 2/8ths of the sky (FEW). Higher clouds at 3,000 feet obscure an additional 1/8th of the sky, and because the observer cannot see above the 1,200-foot layer, he is to assume that the higher 3,000-foot layer also exists above the lower layer (SCT). The highest clouds at 5,000 feet obscure 2/8ths of the sky, and again since the observer cannot see past the 1,200 and 3,000-foot layers, he is to assume the higher 5,000-foot layer also exists above the lower layers (BKN). The sky condition group would be coded as: FEW012 SCT030 BKN050. At manual stations, cumulonimbus (CB) or towering cumulus (TCU) is appended to the associated layer. For example, a scattered layer of towering cumulus at 1,500 feet would be coded SCT015TCU and would be followed by a space if there were additional higher layers to code. Examples: SKC No layers are present CLR No layers are detected at or below 12,000 feet AGL FEW004 Few at 400 feet AGL SCT023TCU Scattered layer of towering cumulus at 2,300 feet BKN105 Broken layer ( ceiling) at 10,500 feet OVC250 Overcast layer ( ceiling) at 25,000 feet VV001 Indefinite ceiling with a vertical visibility of 100 feet FEW012 SCT046 Few clouds at 1,200 feet, scattered layer at 4,600 feet SCT033 BKN085 Scattered layer at 3,300 feet, broken layer ( ceiling) at 8,500 feet SCT018 OVC032CB Scattered layer at 1,800 feet, overcast layer ( ceiling) of cumulonimbus at 7,500 feet SCT009 SCT024 BKN048 Scattered layer at 900 feet, scattered layer at 2,400 feet, broken layer (ceiling) at 4,800 feet AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-14 ### Page 49 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.10 Temperature/Dew Point Group METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Temperature is the degree of hotness or coldness of the ambient air seems as measured by a suitable instrument. Dew point is the temperature to which a given parcel of air must be cooled at constant pressure and constant water vapor content for the air to become fully saturated. Temperature and dew point are coded as two digits rounded to the nearest whole degree Celsius. For example, a temperature of 0.3ºC would be coded at 00. Sub-zero temperatures and dew points are prefixed with an M. For example, a temperature of 4ºC with a dew point of – 2ºC would be coded as 04/M02; a temperature of –2ºC would be coded as M02. If temperature is not available, the entire temperature/dew point group is not coded. If dew point is not available, temperature is coded followed by a solidus, /, and no entry made for dew point. For example, a temperature of 1.5ºC and a missing dew point would be coded as 02/. 3.1.3.11 Altimeter METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 The altimeter setting group codes the current pressure at elevation. This setting is then used by aircraft altimeters to determine the true altitude above a fixed plane of mean sea level. The altimeter group always starts with an A (the international indicator for altimeter in inches of mercury) and is followed by the four digit group representing the pressure in tens, units, tenths, and hundredths of inches of mercury. The decimal point is not coded. For example, an altimeter setting of 29.92 inches of Mercury would be coded as A2992. 3.1.3.12 Remarks (RMK) METAR KOKC 011955Z AUTO 22015G25KT 180V250 3/4SM R17L/2600FT +TSRA BR OVC010CB 18/16 A2992 RMK AO2 TSB25 TS OHD MOV E SLP132 Remarks are included in all METAR and SPECI, when appropriate. Remarks are separated from the body of the report by the contraction RMK. When no remarks are necessary, the contraction RMK is not required. METAR/SPECI remarks fall into two categories: (1) Automated, Manual, and Plain Language, and (2) Additive Maintenance Data. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-15 ### Page 50 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-5. METAR/SPECI Order of Remarks Automated, Manual, and Plain Language Additive and Automated Maintenance Data 1. Volcanic Eruptions 14. Hailstone Size 27. Precipitation* 2. Funnel Cloud 15. Virga 28. Cloud Types* 3. Type of Automated Station 16. Variable Ceiling Height 29. Duration of Sunshine* 4. Peak Wind 17. Obscurations 30. Hourly Temperature and Dew Point 5. Wind Shift 18. Variable Sky Condition 31. 6-Hourly Maximum Temperature* 6. Tower or Surface Visibility 19. Significant Cloud Types 32. 6-Hourly Minimum Temperature* 7. Variable Prevailing Visibility 20. Ceiling Height at Second Location 33. 24-Hour Maximum and Minimum Temperature* 8. Sector Visibility 21. Pressure Rising or Falling Rapidly 34. 3-Hourly Pressure Tendency* 9. Visibility at Second Location 22. Sea-Level Pressure 35. Sensor Status Indicators 10. Lightning 23. Aircraft Mishap 36. Maintenance Indicator 11. Beginning and Ending of Precipitation 24. No SPECI Reports Taken Note: Additive data is primarily used by the National Weather Service for climatological purposes. * These groups should have no direct impact on the aviation community and will not be discussed in this document. 12. Beginning and Ending of Thunderstorms 25. Snow Increasing Rapidly 13. Thunderstorm Location 26. Other Significant Information Remarks are made in accordance with the following: • Time entries are made in minutes past the hour if the time reported occurs during the same hour the observation is taken. Hours and minutes are used if the hour is different; • Present weather coded in the body of the report as VC may be further described, i.e., direction from the station, if known. Weather phenomena beyond 10 statute miles of the point(s) of observation are coded as distant (DSNT) followed by the direction from the station. For example, precipitation of unknown intensity within 10 statute miles east of the station would be coded as VCSH E; lightning 25 statute miles west of the station would be coded as LTG DSNT W; • Distance remarks are in statute miles except for automated lightning remarks which are in nautical miles; AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-16 ### Page 51 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • Movement of clouds or weather, when known, is coded with respect to the direction toward which the phenomena are moving. For example, a thunderstorm moving toward the northeast would be coded as TS MOV NE; • Directions use the eight points of the compass coded in a clockwise order; and • Insofar as possible, remarks are entered in the order they are presented in the following paragraphs (and Table 3-5). 3.1.3.13 Automated, Manual, and Plain Language Remarks These remarks generally elaborate on parameters reported in the body of the report. Automated and manual remarks may be generated either by an automated station or observer. Plain language remarks are only provided from an observer. 3.1.3.13.1 Volcanic Eruptions (Plain Language) Volcanic eruptions are coded in plain language and contain the following, when known: • Name of volcano • Latitude and longitude or the direction and approximate distance from the station • Date/Time (UTC) of the eruption • Size description, approximate height, and direction of movement of the ash cloud • Any other pertinent data about the eruption For example, a remark on a volcanic eruption would look like the following: MT. AUGUSTINE VOLCANO 70 MILES SW ERUPTED AT 231505 LARGE ASH CLOUD EXTENDING TO APRX 30000 FEET MOVING NE. Pre-eruption volcanic activity is not coded. Pre-eruption refers to unusual and/or increasing volcanic activity which could presage a volcanic eruption. 3.1.3.13.2 Funnel Cloud At manual stations, tornadoes, funnel clouds, and waterspouts are coded in the following format: Tornadic activity, TORNADO, FUNNEL CLOUD, or WATERSPOUT, followed by the beginning and/or ending time, followed by the location and/or direction of the phenomena from the station, and/or movement, when known. For example, TORNADO B13 6 NE would indicate that a tornado began at 13 minutes past the hour and was 6 statute miles northeast of the station. 3.1.3.13.3 Type of Automated Station AO1 or AO2 are coded in all METAR/SPECI from automated stations. Automated stations without a precipitation discriminator are identified as AO1; automated stations with a precipitation discriminator are identified as AO2. 3.1.3.13.4 Peak Wind Peak wind is coded in the following format: the remark identifier PK WND, followed by the direction of the wind (first three digits), peak wind speed (next two or three digits) since the last METAR, and the time of occurrence. A space is between the two elements of the remark identifier and the wind direction/speed group; a solidus, /, (without spaces) separates the wind AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-17 ### Page 52 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) direction/speed group and the time. For example, a peak wind of 45 knots from 280 degrees which occurred at 15 minutes past the hour is coded PK WND 28045/15. 3.1.3.13.5 Wind Shift Wind shift is coded in the format: the remark identifier WSHFT, followed by the time the wind shift began. The contraction FROPA is entered following the time if there is reasonable data to consider the wind shift was the result of a frontal passage. A space is between the remark identifier and the time and, if applicable, between the time and the frontal passage contraction. For example, a remark reporting a wind shift accompanied by a frontal passage that began at 30 minutes after the hour would be coded as WSHFT 30 FROPA. 3.1.3.13.6 Tower or Surface Visibility Tower or surface visibility is coded in the following format: tower TWR VIS or surface SFC, followed by the observed tower/surface visibility value. A space is coded between each of the remark elements. For example, the control tower visibility of 1 ½ statute miles would be coded TWR VIS 1 1/2. 3.1.3.13.7 Variable Prevailing Visibility Variable prevailing visibility is coded in the following format: the remark identifier VIS, followed the lowest and highest visibilities evaluated separated by the letter V. A space follows the remark identifier and no spaces are between the letter V and the lowest/highest values. For example, a visibility that was varying between 1/2 and 2 statute miles would be coded VIS 1/2V2. 3.1.3.13.8 Sector Visibility (Plain Language) Sector visibility is coded in the following format: the remark identifier VIS, followed by the sector referenced to 8 points of the compass, and the sector visibility in statute miles. For example, a visibility of 2 1/2 statute miles in the northeastern octant is coded VIS NE 2 1/2. 3.1.3.13.9 Visibility at Second Location At designated automated stations, the visibility at a second location is coded in the following format: the remark identifier VIS, followed by the measured visibility value and the specific location of the visibility sensor(s) at the station. This remark will only be generated when the condition is lower than that contained in the body of the report. For example, a visibility of 2 1/2 statute miles measured by a second sensor located at runway 11 is coded VIS 2 1/2 RWY11. 3.1.3.13.10 Lightning When lightning is observed at a manual station, the frequency, type of lightning and location is reported. The contractions for the type and frequency of lightning are based on Table 3-6, for example, OCNL LTGICCG NW, FRQ LTG VC, or LTG DSNT W. When lightning is detected by an automated system: • Within 5 nautical miles of the Airport Location Point (ALP), it is reported as TS in the body of the report with no remark; • Between 5 and 10 nautical miles of the ALP, it is reported as VCTS in the body of the report with no remark; and • Beyond 10 but less than 30 nautical miles of the ALP, it is reported in remarks only as LTG DSNT followed by the direction from the ALP. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-18 ### Page 53 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-6. METAR/SPECI Type and Frequency of Lightning Type of Lightning Type Contraction Definition Cloud-ground CG Lightning occurring between cloud and ground. In-cloud IC Lightning which takes place within the cloud. Cloud-cloud CC Streaks of lightning reaching from one cloud to another. Cloud-air CA Streaks of lightning which pass from a cloud to the air, but do not strike the ground. Frequency of Lightning Frequency Contraction Definition Occasional OCNL Less than 1 flash/minute. Frequent FRQ About 1 to 6 flashes/minute. Continuous CONS More than 6 flashes/minute. 3.1.3.13.11 Beginning and Ending of Precipitation At designated stations, the beginning and ending time of precipitation is coded in the following format: the type of precipitation, followed by either a B for beginning or an E for ending, and the time of occurrence. No spaces are coded between the elements. The coded times of the precipitation start and stop times are found in the remarks section of the next METAR. The times are not required to be in the SPECI. The intensity qualifiers are coded. For example, if rain began at 0005 and ended at 0030 and then snow began at 0020 and ended at 0055, the remarks would be coded as RAB05E30SNB20E55. If the precipitation were showery, the remark is coded SHRAB05E30SHSNB20E55. If rain ended and snow began at 0042, the remark would be coded as RAESNB42. 3.1.3.13.12 Beginning and Ending of Thunderstorms The beginning and ending of thunderstorms are coded in the following format: TS for thunderstorms, followed by either a B for beginning or an E for ending and the time of occurrence. No spaces are between the elements. For example, if a thunderstorm began at 0159 and ended at 0230, the remark is coded TSB0159E30. 3.1.3.13.13 Thunderstorm Location (Plain Language) Thunderstorm locations are coded in the following format: the thunderstorm identifier, TS, followed by location of the thunderstorm(s) from the station and the direction of movement when known. For example, a thunderstorm southeast of the station and moving toward the northeast is coded TS SE MOV NE. 3.1.3.13.14 Hailstone Size (Plain Language) At designated stations the hailstone size is coded in the following format: the hail identifier GR, followed by the size of the largest hailstone. The hailstone size is coded in ¼ inch increments. For example, GR 1 3/4 would indicate that the largest hailstone were 1 ¾ inches in diameter. If small hail or snow pellets, GS, is coded in the body of the report, no hailstone size remark is required. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-19 ### Page 54 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.13.15 Virga (Plain Language) Virga is coded in the following format: the identifier VIRGA, followed by the direction from the station. The direction of the phenomena from the station is optional, e.g., VIRGA or VIRGA SW. 3.1.3.13.16 Variable Ceiling Height The variable ceiling height is coded in the following format: the identifier CIG, followed by the lowest ceiling height recorded, V denoting variability between two values, and ending with the highest ceiling height. A single space follows the identifier with no other spaces between the letter V and the lowest/highest ceiling values. For example, CIG 005V010 would indicate a ceiling is variable between 500 and 1,000 feet. 3.1.3.13.17 Obscurations (Plain Language) Obscurations, surface-based or aloft, are coded in the following format: the weather identifier causing the obscuration at the surface or aloft followed by the sky cover of the obscuration aloft (FEW, SCT, BKN, OVC) or at the surface (FEW, SCT, BKN), and the height. Surface-based obscurations have a height of 000. A space separates the weather causing the obscuration and the sky cover; no space is between the sky cover and the height. For example, fog hiding 3/8 to 4/8 of the sky is coded FG SCT000; a broken layer at 2,000 feet composed of smoke is coded FU BKN020. 3.1.3.13.18 Variable Sky Condition (Plain Language) Variable sky condition remarks are coded in the following format: the two operationally significant sky conditions (FEW, SCT, BKN, and OVC) separated by spaces and V denoting the variability between the two ranges. If several layers have the same condition amount, the layer height of the variable layer is coded. For example, a cloud layer at 1,400 feet varying between broken and overcast is coded BKN014 V OVC. 3.1.3.13.19 Significant Cloud Types (Plain Language) Significant cloud type remarks are coded in all reports. 3.1.3.13.19.1 Cumulonimbus or Cumulonimbus Mammatus Cumulonimbus or Cumulonimbus Mammatus not associated with thunderstorms are coded in the following format: the cloud type (CB or CBMAM) followed by the direction from the station and the direction of movement when known. The cloud type, location, direction, and direction of movement entries are separated from each other by a space. For example, a CB up to 10 statute miles west of the station moving toward the east would be coded CB W MOV E. If the CB was more than 10 statute miles to the west, the remark is coded CB DSNT W. Cumulonimbus (CB) always evolves from the further development of towering cumulus (TCU). The unusual occurrence of lightning and thunder within or from a CB leads to its popular title, thunderstorm. A thunderstorm usually contains severe or greater turbulence, severe icing, low level wind shear (LLWS), and instrument flight rules (IFR) conditions. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-20 ### Page 55 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 3-5. Cumulonimbus (CB) Example CB always evolves from the further development of towering cumulus (TCU). The usual occurrence of lightning and thunder within or from a CB leads to its popular title, thunderstorm. A thunderstorm usually contains severe or greater turbulence, severe icing, low level wind shear (LLWS), and instrument flight rules (IFR) conditions. (Copyright Robert A. Prentice, 1990) Figure 3-6. Cumulonimbus Mammatus (CBMAM) Example Cumulonimbus Mammatus (CBMAM) (also called mammatus) appears as hanging protuberances, like pouches, on the undersurface of a cloud. (Copyright Robert A. Prentice, 1993) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-21 ### Page 56 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.13.19.2 Towering Cumulus Towering cumulus clouds are coded in the following format: the identifier TCU followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, a towering cumulus cloud up to 10 statute miles west of the station is coded as TCU W. Figure 3-7. Towering Cumulus (TCU) Example Towering Cumulus (TCU). TCU is produced by strong convective updrafts and, thus, indicates turbulence. Icing is typically found above the freezing level. TCU often transforms into cumulonimbus (CB). (Copyright Charles A. Doswell, III, 1977) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-22 ### Page 57 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.13.19.3 Altocumulus Castellanus Altocumulus Castellanus is coded in the following format: the identifier ACC followed by direction from the station. The cloud type and direction entries are separated by a space. For example, an altocumulus cloud 5 to 10 statute miles northwest of the station is coded ACC NW. Figure 3-8. Altocumulus Castellanus (ACC) Example Altocumulus Castellanus (ACC). ACC indicates convective turbulence aloft from the top of the cloud to its base and usually an undetermined height below cloud base as well. (Photo courtesy of National Severe Storms Laboratory/University of Oklahoma) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-23 ### Page 58 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.13.19.4 Standing Lenticular or Rotor Clouds Stratocumulus (SCSL), altocumulus (ACSL), or cirrocumulus (CCSL), or rotor clouds are coded in the following format: the cloud type followed by the direction from the station. The cloud type and direction entries are separated by a space. For example, altocumulus standing lenticular clouds observed southwest through west of the station are coded ACSL SW-W; an apparent rotor cloud 5 to 10 statute miles northeast of the station is coded APRNT ROTOR CLD NE; and cirrocumulus clouds south of the station are coded CCSL S. Figure 3-9. Standing Lenticular and Rotor Clouds Example From top to bottom: Cirrocumulus standing lenticular (CCSL), altocumulus standing lenticular (ACSL), and rotor cloud. These clouds are characteristic of mountain waves. Mountain waves can occasionally produce violent downslope windstorms. Intense mountain waves can present a significant hazard to aviation by producing severe or even extreme turbulence that extends upward into the lower stratosphere. 3.1.3.13.20 Ceiling Height at Second Location At designated stations, the ceiling height at a second location is coded in the following format: the identifier CIG followed by the measured height of the ceiling and the specific location of the ceilometer(s) at the station. This remark is only generated when the ceiling is lower than that contained in the body of the report. For example, if the ceiling measured by a second sensor located at runway 11 is broken at 200 feet, the remark would be CIG 002 RWY11. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-24 ### Page 59 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.3.13.21 Pressure Rising or Falling Rapidly At designated stations, the reported pressure is evaluated to determine if a pressure change is occurring. If the pressure is rising or falling at a rate of at least 0.06 inch per hour and the pressure change totals 0.02 inch or more at the time of the observation, a pressure change remark is reported. When the pressure is rising or falling rapidly at the time of observation, the remark PRESRR (pressure rising rapidly) or PRESFR (pressure falling rapidly) is included in the remarks. 3.1.3.13.22 Sea-Level Pressure At designated stations, the sea-level pressure is coded in the following format: the identifier SLP immediately followed by the sea level pressure in hectopascals. The hundreds and thousands units are not coded and must be inferred. For example, a sea-level pressure of 998.2 hectopascals is coded as SLP982. A sea-level pressure of 1013.2 hectopascals would be coded as SLP132. For a METAR, if sea-level pressure is not available, it is coded as SLPNO. 3.1.3.13.23 Aircraft Mishap (Plain Language) If a SPECI report is taken to document weather conditions when notified of an aircraft mishap, the remark ACFT MSHP is coded in the report but the SPECI not transmitted. 3.1.3.13.24 No SPECI Reports Taken (Plain Language) At manual stations where SPECIs are not taken, the remark NOSPECI is coded to indicate no changes in weather conditions will be reported until the next METAR. 3.1.3.13.25 Snow Increasing Rapidly At designated stations, the snow increasing rapidly remark is reported, in the NEXT METAR, whenever the snow depth increases by 1 inch or more in the past hour. The remark is coded in the following format: the remark indicator SNINCR, the depth increase in the past hour, and the total depth of snow on the ground at the time of the report. The depth of snow increase in the past hour and the total depth on the ground are separated from each other by a solidus, /. For example, a snow depth increase of 2 inches in the past hour with a total depth on the ground of 10 inches is coded SNINCR 2/10. 3.1.3.13.26 Other Significant Information (Plain Language) Agencies may add to a report other information significant to their operations, such as information on fog dispersal operations, runway conditions, FIRST or LAST reports from station, etc. 3.1.3.14 Additive and Automated Maintenance Data Additive data groups (Table 3-5) are only reported at designated stations and are primarily used by the NWS for climatological purposes. Most have no direct impact on the aviation community but a few are discussed below. 3.1.3.14.1 Hourly Temperature and Dew Point At designated stations, the hourly temperature and dew point group are further coded to the tenth of a degree Celsius. For example, a recorded temperature of +2.6ºC and dew point of -1.5ºC would be coded as T00261015. The format for the coding is as follows: AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-25 ### Page 60 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) T Group indicator 0 Indicates the following number is positive; a 1 would be used if the temperature was reported as negative at the time of observation 026 Temperature disseminated to the nearest 10 th and read as 02.6 1 Indicates the following number is negative; a 0 would be used if the number was reported as positive at the time of observation 015 Dew Point disseminated to the nearest 10th and read as 01.5 No spaces are between the entries. For example, a temperature of 2.6ºC and dew point of – 1.5ºC is reported in the body of the report as 03/M01 and the hourly temperature and dew point group as T00261015. If the dew point is missing only the temperature is reported; if the temperature is missing the hourly temperature and dew point group is not reported. 3.1.3.14.2 Maintenance Data Groups The following maintenance data groups, Sensor Status Indicators and the Maintenance Indicator, are only reported from automated stations. 3.1.3.14.2.1 Sensor Status Indicators Sensor status indicators are reported as indicated below: • If the Runway Visual Range is missing and would normally be reported, RVRNO is coded • When automated stations are equipped with a present weather identifier and the sensor is not operating, the remark PWINO is coded • When automated stations are equipped with a tipping bucket rain gauge and the sensor is not operating, PNO is coded • When automated stations are equipped with a freezing rain sensor and the sensor is not operating, the remark FZRANO is coded • When automated stations are equipped with a lightning detection system and the sensor is not operating, the remark TSNO is coded • When automated stations are equipped with a secondary visibility sensor and the sensor is not operating, the remark VISNO LOC is coded • When automated stations are equipped with a secondary ceiling height indicator and the sensor is not operating, the remark CHINO LOC is coded 3.1.3.14.2.2 Maintenance Indicator A maintenance indicator, $, is coded when an automated system detects maintenance is needed on the system. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-26 ### Page 61 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.1.4 METAR/SPECI Examples **METAR PAHL 031836Z AUTO 07009KT 10SM CLR 13/02 A2980 RMK AO1 PNO** GROUP CODED TRANSLATION Type of Report METAR Aviation Routine Weather Report Station Identifier PAHL United States Huslia, Alaska Date and Time of Report 031836Z 3rd day of the month, 1836 UTC Report Modifier AUTO automated observation with no human augmentation Wind 07009KT Wind from 070 degrees (the east) at 9 knots (10 mph, 4.6 m/s) Visibility 10SM Visibility ten statute miles (16 kilometers) Runway Visual Range [omitted] Present Weather [omitted] There may or may not be significant weather present at this time Sky Condition CLR Sky clear below 12,000 feet AGL Temperature/Dewpoint 13/02 Temperature 13°C (55°F), dewpoint 2°C (36°F) Altimeter A2980 29.80 inches of mercury (1009.2 millibars, 1009.2 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language A01 Automated station without a precipitation discriminator Additive and Automated Maintenance Data PNO Tipping bucket rain gauge not operating **METAR KNSI 031656Z VRB03KT 5SM HZ SCT007 21/17 A2989 RMK SLP121 T02060172** GROUP CODED TRANSLATION Type of Report METAR Aviation Routine Weather Report Station Identifier KNSI United States San Nicolas Island, California Date and Time of Report 031656Z 3rd day of the month, 1656 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind VRB03KT Wind variable at 3 knots (4 mph, 1.5 m/s) Visibility 5SM Visibility five statute miles (8.0 kilometers) Runway Visual Range [omitted] Present Weather HZ Haze Sky Condition SCT007 Scattered at 700 feet AGL Temperature/Dewpoint 21/17 Temperature 21°C (69°F), dewpoint 17°C (63°F) Altimeter A2989 29.89 inches of mercury (1012.3 millibars, 1012.3 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language SLP121 Sea level pressure 1012.1 hectopascals (1012.1 millibars) Additive and Automated Maintenance Data T02060172 Temperature 20.6°C (69°F), dewpoint 17.2°C (63°F) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-27 ### Page 62 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) SPECI KCOT 292020Z AUTO 13009KT 3SM TSRA BR SCT011 BKN028 OVC043 23/21 A2991 RMK AO2 PK WND 13029/2000 LTG DSNT ALQDS P0020 GROUP CODED TRANSLATION Type of Report SPECI Aviation Selected Special Weather Report Station Identifier KCOT United States Cotulla, Texas Date and Time of Report 292020Z 29th day of the month, 2020 UTC Report Modifier AUTO Automated observation with no human augmentation Wind 13009KT Wind from 130 degrees (the southeast) at 9 knots (10 mph, 4.7 m/s) Visibility 3SM Visibility three statute miles (5 kilometers) Runway Visual Range [omitted] Present Weather TSRA BR Thunderstorm, moderate rain, mist Sky Condition SCT011 BKN028 OVC043 Scattered at 11,000 feet AGL, Ceiling broken at 2,800 feet AGL, Overcast at 4,300 feet AGL Temperature/Dewpoint 23/21 Temperature 23°C (73°F), dewpoint 21°C (70°F) Altimeter A2991 29.91 inches of mercury (1013.0 millibars, 1013.0 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language AO2 Automated station with a precipitation discriminator PK WND 13029/2000 Peak wind from 130 degrees (the southeast) at 29 knots (33 mph, 14.9 m/s) occurred at 2000 UTC LTG DSNT ALQDS Lightning distant all quadrants Additive and Automated Maintenance Data P0020 0.20 inches of precipitation fell in the past hour AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-28 ### Page 63 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) METAR KMDW 090153Z 23003KT 1/2SM R31C/4000V4500FT SN FZFG VV002 M04/M05 A3004 RMK AO2 SLP191 SNINCR 1/10 P0000 T10391050 GROUP CODED TRANSLATION Type of Report METAR Aviation Routine Weather Report Station Identifier KCOT United States Chicago (Midway), Illinois Date and Time of Report 090153Z 9th day of the month,0153 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind 23003KT Wind from 230 degrees (the southwest) at 3 knots (3 mph,1.6 m/s) Visibility 1/2SM Visibility one-half statute miles (0.8 kilometers) Runway Visual Range R31C/4000V4500FT Runway 31 center visual range variable between 4,000 and 4,5000 feet Present Weather SN FZFG Snow, freezing fog Sky Condition VV002 Indefinite ceiling, vertical visibility 200 feet Temperature/Dewpoint M04/M05 Temperature -4°C (25°F), dewpoint -5°C (23°F) Altimeter A3004 Altimeter 30.04 inches of mercury (1017.4 hectopascals, 1017.4 millibars) Remarks RMK Remarks section designator Automated, Manual, and Plain Language A02 Automated station with a precipitation discriminator SLP191 Sea level pressure 1019.1 hectopascals (1019.1 millibars) SNINCR 1/10 Snow increasing rapidly, snow depth increase of 1 inch in the past hour, a total depth on the ground of 10 inches Additive and Automated Maintenance Data P0000 Less than 1/100 of an inch of precipitation fell in the past hour T10391050 Temperature -3.9°C (25°F), dewpoint - 5.0°C (23°F) AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-29 ### Page 64 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) SPECI KMEM 091826 27013G27KT 240V310 1/2SM R36L/1000VP6000FT +TSRAGR FG FEW002 BKN023 OVC032CB 18/17 A2992 RMK A02 PK WND 31031/1802 WSHFT 1759 TSB22RAB17GRB23 PRESRR FRQ LTGIC W-NW TS W-NW GR 1/2 P0005 GROUP CODED TRANSLATION Type of Report SPECI Aviation Selected Special Weather Report Station Identifier KMEM United States Memphis, Tennessee Date and Time of Report 091826Z 9th day of the month, 1826 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind 27013G27KT 240V310 Wind from 270 degrees (the west) at 13 knots (15 mph, 6.7 m/s) gusting to 27 knots (31 mph, 13.9 m/s), wind variable between 240 degrees (the westsouthwest) and 310 degrees (the northwest) Visibility 1/2SM Visibility one-half statute miles (0.8 kilometers) Runway Visual Range R36L/1000VP6000FT Runway 36 left visual range variable between 1,000 and more than 6,000 feet Present Weather +TSRAGR FG Thunderstorm, heavy rain, hail, fog Sky Condition FEW002 BKN023 OVC032CB Few at 200 feet AGL, ceiling broken at 2,300 feet AGL, overcast at 3,200 feet AGL cumulonimbus Temperature/Dewpoint 18/17 Temperature 18°C (64°F), dewpoint 17°C (63°F) Altimeter A2992 29.92 inches of mercury (1013.2 millibars, 1013.2 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language AO2 Automated station with a precipitation discriminator PK WND 31031/1802 Peak wind from 310 degrees (the northwest) at 31 knots (36 mph, 15.9 m/s) occurred at 1802 or 2 minutes past the hour UTC WSHFT 1759 Wind shift occurred at 1759 UTC TSB22RAB17GRB23 Thunderstorm began at 22 minutes past the hour, rain began at 17 minutes past the hour, hail began at 23 minutes past the hour PRESRR Pressure rising rapidly FRQ LTGIC W-NW Frequent lightning in-cloud west through northwest TS W-NW Thunderstorm west through northwest GR1/2 Largest hailstone 1/2 inches in diameter Additive and Automated Maintenance Data P0005 0.05 inches of precipitation fell in the past hour AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-30 ### Page 65 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) SPECI KMSN 012312Z 13021G26KT 1SM -FZRAPL BR OVC011 00/M02 A2988 RMK AO2 PK WND 14031/2255 SFC VIS 1 1/2 P0005 $ GROUP CODED TRANSLATION Type of Report SPECI Aviation Selected Special Weather Report Station Identifier KMSN United States Madison, Wisconsin Date and Time of Report 012312Z 1st day of the month, 2312 UTC Report Modifier [omitted] Either a manual or an augmented observation Wind 13021G26KT Wind from 130 degrees (the southeast) at 21 knots (24 mph, 10.8 m/s) gusting to 26 knots (30 mph, 13.4 m/s) Visibility 1SM Visibility one statute mile (1.6 kilometers) Runway Visual Range [omitted] Present Weather -FZRAPL BR Light freezing rain, ice pellets, mist Sky Condition OVC011 Ceiling overcast at 1,100 feet AGL Temperature/Dewpoint 00/M02 Temperature 0°C (32°F), dewpoint -2°C (28°F) Altimeter A2988 29.88 inches of mercury (1011.9 millibars, 1011.9 hectopascals) Remarks RMK Remarks section designator Automated, Manual, and Plain Language AO2 Automated station with a precipitation discriminator PK WND 14031/2255 Peak wind from 140 degrees (the southeast) at 31 knots (36 mph, 15.9 m/s) occurred at 2255 UTC SFC VIS 1 1/2 Surface visibility one and on-half statute mile Additive and Automated Maintenance Data P0005 0.05 inches of precipitation fell in the past hour $ Maintenance is needed on the system AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-31 ### Page 66 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.2 Pilot Weather Reports (PIREP) No report is timelier than the one made from the flight deck of aircraft in flight. In fact, aircraft in flight are the only means of observing actual icing and turbulence conditions. Pilots welcome pilot weather reports (PIREPs) as well as pilot weather briefers and forecasters. Pilots should report any observation, good or bad, to assist other pilots with flight planning and preparation. If conditions were forecasted to occur but not encountered, a pilot should also report this inaccuracy. This will help the NWS verify forecast products and create more accurate products for the aviation community. Pilots should help themselves, the aviation public, and the aviation weather forecasters by providing PIREPs. Pipe Up with a PIREP and help the aviation community operate more safely and effectively. PIREPs are available in the internet at the Aviation Digital Data Service (ADDS) web page at: http://adds.aviationweather.gov/pireps/ 3.2.1 Format A PIREP is transmitted in a prescribed format (Figure 3-7). Required elements for all PIREPs are: message type, location, time, altitude/flight level, type aircraft, and at least one other element to describe the reported phenomena. The other elements will be omitted when no data is reported with them. All altitude references are mean sea level (MSL) unless otherwise noted. Distance for visibility is in statute miles and all other distances are in nautical miles. Time is reported in Universal Time Coordinated (UTC). Figure 3-10. Pilot Weather Report (PIREP) Coding Format 3.2.1.1 Message Type (UUA/UA) The two types of PIREPs are Urgent (UUA) and Routine (UA). 3.2.1.1.1 Urgent PIREPs Urgent (UUA) PIREPs contain information about: AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-32 ### Page 67 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • Tornadoes, funnel clouds, or waterspouts • Severe or extreme turbulence (including Clear Air Turbulence) • Severe icing • Hail • Low Level Wind Shear (LLWS ) within 2,000 feet of the surface. LLWS PIREPS are classified as UUA if the pilot reports air speed fluctuations of 10 knots or more or if air speed fluctuations are not reported but LLWS is reported, the PIREP is classified as UUA. • Volcanic ash clouds • Any other weather phenomena reported which are considered by the briefer as being hazardous, or potentially hazardous, to flight operations. 3.2.1.1.2 Routine PIREPs Routine PIREPs are issued after receiving a report from a pilot that does not contain any urgent information as listed in Section 3.2.1.1.1. 3.2.1.2 Location (/OV) The Location (/OV) can be referenced either by geographical position or by route segment. 3.2.1.2.1 Location Location can be referenced to a VHF NAVAID or an airport, using either the three-letter International Air Transport Association (IATA) or four letter International Civil Aviation Organization (ICAO) identifier. If appropriate, the PIREP is encoded using the identifier, then three digits to define a radial and three digits to define the distance in nautical miles. Examples: /OV APE Over Appleton VOR /OV KJFK Over John F. Kennedy International Airport, New York City, NY /OV APE230010 230 degrees at 10 nautical miles from the Appleton VOR /OV KJFK107080 107 degrees at 80 nautical miles fr om John F. Kennedy International Airport, New York City, New York 3.2.1.2.1.1 3.2.1.3.1.1 Route Segment A PIREP can also be referenced using two or more fixes to describe a route. Examples: /OV KSTL-KMKC From Lambert-Saint Louis International Airport, Missouri to Charles B. Wheeler Downtown Airport, Kansas City, Missouri /OV KSTL090030-KMKC045015 From 90 degrees at 30 nautical miles from Lambert- Saint Louis International Airport, Missouri to 45 degrees at 15 nautical miles from Charles B. Wheeler Downtown Airport, Kansas City, Missouri AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-33 ### Page 68 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.2.1.3 Time (/TM) Time (/TM) is the time that the reported phenomenon occurred or was encountered. It is coded in four digits UTC. Example: /TM 1315 1315 UTC 3.2.1.4 Altitude/Flight Level (/FL) The Altitude/Flight Level (/FL) is the altitude in hundreds of feet MSL where the phenomenon was first encountered. If not known, UNKN is entered. If the aircraft was climbing or descending, the appropriate contraction (DURC or DURD) is entered in the remarks (/RM). If the condition was encountered within a layer, the altitude range is entered within the appropriate element that describes the condition. Examples: /FL085 8,500 feet MSL /FL310 Flight Level 310 /FLUNKN /RM DURC Flight Level unknown, remarks, during climb 3.2.1.5 Aircraft Type (/TP) Aircraft Type (/TP) is entered. If not known, UNKN is entered. Icing and turbulence reports always include aircraft type. Examples: /TP BE20 Super King Air 200 /TP SR22 Cirrus 22 /TP P28R Piper Arrow /TP UNKN Type unknown 3.2.1.6 Sky Condition (/SK) Sky Condition (/SK) group is used to report height of cloud bases, tops, and cloud cover. The height of the base of a layer of clouds is coded in hundreds of feet MSL. The top of a layer is entered in hundreds of feet MSL preceded by the word -TOP. If reported as clear above the highest cloud layer, SKC is coded following the reported level. Examples: /BKN040-TOP065 Base of broken layer 4,000 feet MSL, top 6,500 feet MSL /SK OVC100-TOP110/ SKC Base of an overcast layer 10,000 feet MSL, top 11,000 feet MSL, clear above /SK OVC015-TOP035/OVC230 Base of an overcast layer 1,500 feet MSL, top 3,500 feet MSL, base of an overcast layer 23,000 feet MSL /SK OVC-TOP085 Overcast layer, top 8,500 feet MSL Cloud cover amount ranges are entered with a hyphen separating the amounts; i.e., BKN-OVC. Examples: AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-34 ### Page 69 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) /SK SCT-BKN050-TOP100 Base of a scattered to broken layer 5,000 feet MSL, top 10,000 feet MSL /SK BKN-OVCUNKN-TOP060/BKN120-TOP150/ SKC Base of a broken to overcast layer unknown, top 6,000 feet MSL, base of a broken layer 12,000 feet MSL, top 15,000 feet MSL, clear above Unknown heights are indicated by the contraction UNKN. Example: /SK OVC065-TOPUNKN Base of an overcast layer 6,500 feet MSL, top unknown If a pilot indicates he/she is in the clouds, IMC is entered. Example: /SK OVC065-TOPUNKN /RM IMC Base of an overcast layer 6,500 feet MSL, top unknown, remark, in the clouds When more than one layer is reported, layers are separated by a solidus (/). 3.2.1.7 Flight Visibility and Weather (/WX) Weather conditions encountered by the pilot are reported as follows: Flight visibility, when reported, is entered first in the /WX field. It is coded as FV followed by a two-digit visibility value rounded down, if necessary, to the nearest whole statute mile and appended with SM (FV03SM). If visibility is reported as unrestricted, FV99SM is entered. Flight weather types are entered using one or more of the standard surface weather reporting symbols contained in Table 3-7. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-35 ### Page 70 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-7. PIREP Weather Type and Symbols Type METAR Code Drifting / Blowing Snow DRSN/BLSN Drifting Dust DRDU Drifting Sand DRSA Drizzle/Freezing Drizzle DZ/FZDZ Dust / Blowing Dust DU/BLDU Duststorm DS Fog (visibility less than 5/8SM) FG Freezing Fog FZFG Freezing Rain FZRA Funnel Cloud FC Hail (Approximately ¼-inch diameter or more) GR Hail Shower SHGR Haze HZ Ice Crystals IC Ice Pellets/Showers PL/SHPL Mist (visibility great than or equal to 5/8SM) BR Patchy Fog BCFG Patchy Fog on part of airport PRFG Rain/Showers RA/SHRA Sand/Blowing Sand SA/BLSA Sandstorms SS Shallow Fog MIFG Small Hail/Snow Pellet Showers SHGS Small Hail/Snow Pellets GS Smoke FU Snow Grains SG Snow / Showers SN/SHSN Spray PY Squalls SQ Thunderstorm TS Tornado/Waterspout +FC Unknown Precipitation UP Volcanic Ash VA Well developed Dust/Sand Whirls PO Intensity modifiers for precipitation (- for light, no qualifier for moderate, and + for heavy) indicates precipitation type, except ice crystals and hail, including those associated with a thunderstorm and those of a showery nature. Intensity modifiers for obscurations are ascribed as moderate or heavy (+) for dust and sandstorms only. No intensity modifiers are used for blowing dust, blowing sand, or blowing snow. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-36 ### Page 71 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Example: /WV FV01SM +DS000-TOP083/SKC /RM DURC Flight visibility 1 statute mile, base heavy duststorm layer at the surface, top 8,300 feet MSL, clear above, remarks, during climb When more than one form of precipitation is combined in the report, the dominant type is reported first. Examples: /WX FV00SM +TSRAGR Flight visibility zero statute miles, thunderstorm, heavy rain, hail /WX FV02SM BRHZ000-TOP083 Flight visibility 2 statute miles, base of a haze and mist layer at the surface, top 8,300 feet MSL If a funnel cloud is reported, it is coded as FC following /WX group and is spelled out as Funnel Cloud after /RM group. If a tornado or waterspout is reported, it is coded +FC following /WX group and TORNADO or WATERSPOUT is spelled out after the /RM group. Examples: /WX FC /RM FUNNEL CLOUD Funnel cloud, remarks, funnel cloud /WX +FC /RM TORNADO Tornado, remark, tornado When the size of hail is stated, it is coded in 1/4-inch increments in remarks (/RM) group. The proximity qualifier VC (vicinity) is only used with TS, FG, FC, +FC, SH, PO, BLDU, BLSA, and BLSN. Example: /WX FV02SM BLDU000-TOP083 VC W Flight visibility 2 statute miles, base of a blowing dust layer at the surface, top 8,300 feet MSL in the vicinity, west When more than one type of weather is reported, they are reported in the following order: • TORNADO, WATERSPOUT, or FUNNEL CLOUD • Thunderstorm with or without associated precipitation • Weather phenomena in order of decreasing predominance. No more than three groups are used in a single PIREP. Weather layers are entered with the base and/or top of the layer when reported. The same format as in the sky condition (/SK) group is used. Example: /WX FU002-TOP030 Base of a smoke layer, 200 feet MSL, top 3,000 feet MSL AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-37 ### Page 72 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.2.1.8 Air Temperature (/TA) Outside air temperature (/TA) is reported using two digits in degrees Celsius. Negative temperatures is prefixed with an M; e.g., /TA 08 or /TA M08. 3.2.1.9 Wind Direction and Speed (/WV) Wind direction and speed is encoded using three digits to indicate wind direction (magnetic) and two or three digits to indicate reported wind speed. When the reported speed is less than 10 knots, a leading zero is used. The wind group will always have KT appended to represent the units in knots. Examples: /WV 02009KT Wind 20 degrees (magnetic) at 9 knots /WV 28057KT Wind 280 degrees (magnetic) at 57 knots /WV 350102KT Wind 350 degrees (magnetic) at 102 knots 3.2.1.10 Turbulence (/TB) Turbulence intensity, type, and altitude are reported after wind direction and speed. Intensity is coded first. Duration is coded next if reported by the pilot (intermittent, occasional, continuous) followed by the intensity using contractions LGT, MOD, SEV, or EXTRM. Range or variation of intensity is separated with a hyphen; e.g., MOD-SEV. If turbulence was forecasted, but not encountered, NEG is entered. Type is coded second. CAT (Clear Air Turbulence) or CHOP is entered if reported by the pilot. High-level turbulence (normally above 15,000 feet AGL) not associated with clouds (including thunderstorms) is reported as CAT. Altitude is reported (last) only if it differs from value reported in the Altitude/Flight Level (/FL) group. When a layer of turbulence is reported, height values are separated with a hyphen. If lower or upper limits are not defined, BLO or ABV is used. Examples: /TB LGT Light turbulence /TB LGT 040 Light turbulence at 4,000 feet MSL /TB OCNL MOD-SEV BLO 080 Occasional moderate to severe turbulence below 8,000 feet MSL /TB MOD-SEV CAT 350 Moderate to severe clear air turbulence at 35,000 feet MSL /TB NEG 120-180 Negative turbulence between 12,000 to 18,000 feet MSL /TB CONS MOD CHOP 220/NEG 230-280 Continuous moderate chop at 22,000 feet MSL, negative turbulence between 23,000 to 28,000 feet MSL /TB MOD CAT ABV 290 Moderate clear air turbulence above 29,000 feet MSL Turbulence reports should include location, altitude, or range of altitudes, and aircraft type, and, when reported, whether in clouds or clear air. The pilot determines the degree of turbulence, intensity, and duration (occasional, intermittent, and continuous). The report should be obtained AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-38 ### Page 73 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) and disseminated, when possible, in conformance with the U.S. Standard Turbulence Criteria Table 3-8. Table 3-8. PIREP Turbulence Reporting Criteria Intensity Aircraft Reaction Reaction Inside Aircraft Reporting Term-Definition Light Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw). Report as Light Turbulence;1 or Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude. Report as Light Chop. Occupants may feel a slight strain against belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be conducted and little or no difficulty is encountered in walking. Occasional – Less than 1/3 of the time. Intermittent-1/3 to 2/3 Continuous-More than 2/3 Moderate Turbulence that is similar to Light Turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Report as Moderate Turbulence;1 or Turbulence that is similar to Light Chop but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft or attitude. Report as Moderate Chop.1 Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult. **NOTE** 1. Pilots should report location(s), time (UTC), intensity, weather in or near clouds, altitude, type of aircraft and, when applicable, duration of turbulence. 2. Duration may be based on time between two locations or over a single location. All locations should be readily identifiable. EXAMPLES: Over Omaha. 1232Z, Moderate Turbulence, in cloud, flight Level 310, B737. b. From 50 miles south of Albuquerque to 30 miles north of Phoenix, 1210Z to 1250Z, occasional Moderate Chop, Flight Level 330, DC8. Severe Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence.1 Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food service and walking are impossible. Extreme Turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may cause structural damage. Report as Extreme Turbulence.1 1 High level turbulence (normally above 15,000 feet ASL) not associated with clouds, including thunderstorms, should be reported as CAT (clear air turbulence) preceded by the appropriate intensity, or light or moderate chop. 3.2.1.11 Icing (/IC) Icing intensity, type and altitude is reported after turbulence. Intensity is coded first using contractions TRACE, LGT (light), MOD (moderate), or SEV severe). Reports of a range or variation of intensity is separated with a hyphen. If icing was forecast but not encountered, NEG (negative) is coded. The following table classifies icing intensity according to its operational effects on aircraft. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-39 ### Page 74 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 3-9. Icing Intensities, Contractions, and Airframe Ice Accumulation Intensity Contraction Airframe Ice Accumulation Trace TRACE Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even without the use of deicing/anti-icing equipment unless encountered for an extended period of time (over 1 hour). Light LGT The rate of accumulation may create a problem if flight is prolonged in this environment (over 1 hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used. Moderate MOD The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is necessary. Severe SEV The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary. Icing type is reported second. Reportable types are RIME, CLR (clear), or MX (mixed). The following table classifies icing type according to it description. Table 3-10. Icing Types, Contractions, and Descriptions Icing Type Contraction Description Rime RM Rough, milky, opaque ice formed by the instantaneous freezing of small super-cooled water droplets. Clear CLR A glossy, clear or translucent ice formed by the relatively slow freezing of large super-cooled water droplets. Mixed MX A combination of both rime and clear. The reported icing/altitude is coded (last) only if different from the value reported in the altitude/flight level (/FL) group. A hyphen is used to separate reported layers of icing. ABV (above) or BLO (below) is coded when a layer is not defined. Pilot reports of icing should also include location (/OV), type aircraft (/TP), and air temperature (/TA). Examples: /IC LGT-MOD MX 085 Light to moderate mixed icing, 8,500 feet MSL /IC LGT RIME Light rime icing /IC MOD RIME BLO 095 Moderate rime icing below 9,500 feet MSL /IC SEV CLR 035-062 Severe clear icing 3,500 to 6,200 feet MSL 3.2.1.12 Remarks (/RM) The remarks (/RM) group is used to report a phenomenon which is considered important but does not fit in any of the other groups. This includes, but is not limited to, low-level wind shear AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-40 ### Page 75 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (LLWS) reports, thunderstorm lines, coverage and movement, size of hail (1/4-inch increments), lightning, clouds observed but not encountered, geographical or local description of where the phenomenon occurred, and contrails. Hazardous weather is reported first. LLWS is described to the extent possible. 3.2.1.12.1 Wind Shear Ten knots or more fluctuations in wind speed (+/- 10KTS), within 2,000 feet of the surface, require an Urgent (UUA) pilot report. When Low Level Wind Shear is entered in a pilot report, LLWS is entered as the first remark in the remarks (/RM) group. Example: /RM LLWS +/-15 KT SFC-008 DURC RY22 JFK Remarks, Low Level Wind Shear, air speed fluctuations of plus or minus 15 knots, surface to 800 feet during climb, runway 22, John F. Kennedy International Airport, New York. 3.2.1.12.2 FUNNEL CLOUD, TORNADO, and WATERSPOUT Funnel cloud, tornado, and waterspout are entered with the direction of movement when reported. Example: /RM TORNADO W MOV E Remarks, tornado west moving east 3.2.1.12.3 Thunderstorm Thunderstorm coverage is coded as ISOL (isolated), FEW (few), SCT (scattered), NMRS (numerous) followed by description as LN (line), BKN LN (broken line), SLD LN (solid line) when reported. This is followed with TS, the location and movement, and the type of lightning when reported. Example: /RM NMRS TS S MOV E GR1/2 Remarks, numerous thunderstorms south moving east, hail 1/2–inch in diameter 3.2.1.12.4 Lightning Lightning frequency is coded as OCNL (occasional) or FRQ (frequent), followed by type as LTGIC (lightning in cloud), LTGCC (lightning cloud to cloud), LTGCG (lightning cloud to ground), LTGCA (lightning cloud to air), or combinations, when reported. Example: /RM OCNL LTGICCG Remarks, occasional lighting in cloud, cloud to ground 3.2.1.12.5 Electrical Discharge For an electrical discharge, DISCHARGE is coded followed by the altitude. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-41 ### Page 76 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Example: /RM DISCHARGE 120 Remarks, discharge, 12,000 feet MSL 3.2.1.12.6 Clouds Remarks are used when clouds can be seen but were not encountered and reported in the sky condition group (/SK) Examples: /RM CB E MOV N Remarks, cumulonimbus east moving north /RM OVC BLO Remarks, overcast below 3.2.1.12.7 Plain Language If specific phraseology is not adequate, plain language is used to describe the phenomena or local geographic locations. Remarks that do not fit in other groups like DURC (during climb), DURD (during descent), RCA (reach cruising altitude), TOP, TOC (top of climb), or CONTRAILS are included. Examples: /RM BUMPY VERY ROUGH RIDE /RM CONTRAILS /UA/OV BIS270030/TM 1445/FL060/TP CVLT/TB LGT /RM DONNER SUMMIT PASS 3.2.1.12.8 Volcanic Eruptions Volcanic ash alone is an Urgent PIREP. A report of volcanic activity includes as much information as possible including the name of the mountain, ash cloud and movement, height of the top and bottom of the ash, etc., is included. If the report is received from a source other than a pilot, Aircraft UNKN, Flight Level UNKN, and /RM UNOFFICIAL is entered. Example: /UUA/OV ANC240075/TM 2110/FL370/TP DC10/WX VA/RM VOLCANIC ERUPTION 2008Z MT AUGUSTINE ASH 40S MOV SSE Urgent Pilot Weather Report, 240 degrees at 75 nautical miles from Anchorage International Airport, Alaska, 2110 UTC, flight level 310, a DC10 reported volcanic ash, remarks, volcanic eruption occurred at 2008 UTC Mount Augustine, ash 40 nautical miles south moving southsoutheast. 3.2.1.12.9 SKYSPOTTER The SKYSPOTTER program is a result of a recommendation from the Safer Skies FAA/INDUSTRY Joint Safety Analysis and Implementation Teams. The term SKYSPOTTER indicates a pilot has received specialized training in observing and reporting in-flight weather phenomenon, pilot weather reports, or PIREPs. When a PIREP is received from a pilot identifying themselves as a SKYSPOTTER aircraft, the additional comment “/AWC” is added at the end of the remarks section of the PIREP. Example: AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-42 ### Page 77 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) **PIREP TEXT/RM REMARKS/AWC** 3.2.2 PIREP Examples UUA /OV ORD/TM 1235/FLUNKN/TP B727/TB MOD/RM LLWS +/- 20KT BLW 003 DURD RWY27L Urgent Pilot Weather Report, over Chicago O’Hare Airport, Illinois, 1235 UTC, flight level unknown, from a Boeing 727, moderate turbulence, remarks, Low Level Wind Shear, airspeed fluctuations of plus or minus 20 knots below 300 feet AGL during descent, runway 27 left. **UUA /OV BAM260045/TM 2225/FL180/TP BE20/TB SEV/RM BROKE ALL THE** **BOTTLES IN THE BAR** Urgent Pilot Weather Report, 260 degrees at 45 nautical miles from Hazen VOR, Nevada, 2225 UTC, 18,000 feet MSL, Beech Super King Air 200, severe turbulence, remarks, broke all the bottles in the bar. UA /OV KMRB-KPIT/TM 1600/FL100/TP BE55/SK BKN024-TOP032/BKN-OVC043- TOPUNKN /TA M12/IC LGT-MOD RIME 055-080 Pilot Weather Report, Martinsburg, West Virginia to Pittsburgh International Airport, Pennsylvania, 1600 UTC, 10,000 feet MSL, Beechcraft Baron, base of a broken layer 2,400 feet MSL, top 3,200 feet MSL, base of a broken to overcast layer 4,300 feet MSL, top unknown, temperature minus 12, light to moderate rime ice between 5,500 to 8,000 feet MSL. UA /OV IRW090064/TM 1522/FL080/TP C172/SK SCT090-TOPUNKN/WX FV05SM HZ/TA M04/WV 24040KT/TB LGT/RM IN CLR Pilot Weather Report, 90 degrees and 64 nautical miles from Will Rogers VORTAC, Oklahoma City, Oklahoma, 1522 UTC, 8,000 feet MSL, Cessna 172, base of a scattered layer 9,000 feet MSL, top unknown, flight visibility 5 statute miles, haze, temperature minus 4, wind 240 degrees at 40 knots, light turbulence, remarks, in clear. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-43 ### Page 78 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) UA /OV KLIT-KFSM/TM 0310/FL100/TP BE36/SK SCT070-TOP110/TA M03/WV 25015KT Pilot Weather Report, between Little Rock and Fort Smith, Arkansas, 0310 UTC at 10,000 feet MSL. Beech 36, base of a scattered layer at 7,000 feet MSL, top 11,000 feet MSL, temperature minus 3, wind 250 degrees at 15 knots. UA /OV KAEG/TM 1845/FL UNKN/TP UNKN /RM TIJERAS PASS CLSD DUE TO FG AND LOW CLDS UNA VFR RTN KAEG. Pilot Weather Report, over Double Eagle II Airport, Albuquerque, New Mexico, 1845 UTC, remarks, Tijeras Pass closed due to fog and low clouds, unable to fly VFR, returned to Double Eagle II Airport. **UA /OV ENA14520/TM 2200/FL310/TP B737/TB MOD CAT 350-390.** Pilot Weather Report, 145 degrees at 20 nautical miles from Kenai, Alaska, at 2200 UTC, at flight level 310, Boeing 737, moderate clear air turbulence between 35,000 and 39,000 feet MSL. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-44 ### Page 79 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 3.3 Radar Weather Report (SD/ROB) A Radar Weather Report (SD/ROB) contains information about precipitation observed by weather radar. This is a textual product derived from the WSR-88D NEXRAD radar without human intervention. The resolution of this textual product is very coarse, up to 80 minutes old, and should only be used if no other radar information is available. Figure 3-11. Radar Weather Report (SD/ROB) Coding Format 3.3.1 Format Reports are transmitted hourly from WSR-88D Weather Radar sites (see figure 3-12). The SD/ROB format is presented in Figure 3-8. 3.3.1.1 Location Identifier The location identifier is reported as the three-letter International Air Transport Association (IATA) code. Example: TLX Oklahoma City Twin Lakes, Oklahoma 3.3.1.2 Time The time of the observation is reported in four-digits Universal Time Coordinated (UTC). Example: **1935 1935 UTC** 3.3.1.3 Configuration Three types of configurations can be reported: CELL, LN (line), and AREA. Multiple configurations can be reported within one Weather Radar Report. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-45 ### Page 80 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) A CELL is a single, isolated convective echo. A LN (line) is a convective echo that meets the following criteria: • Contains heavy or greater intensity precipitation • Is at least 30 miles long • Length is at least four times greater than width • Contains at least 25 percent coverage An AREA is a group of echoes of similar type, not classified as a line. Figure 3-9 illustrates the three configurations that can be reported in a Weather Radar Report. Figure 3-12. Radar Weather Report (SD/ROB) Configurations 3.3.1.4 Coverage Coverage of precipitation is coded in single digits representing tenths of coverage. For echo configurations containing multiple precipitation types, coverage is coded for each type. Total coverage is obtained by adding the individual values. Examples: 2TRW+4R 2/10 coverage TRW+, 4/10 coverage R, 6/10 total coverage 3R6S- 3/10 coverage R, 6/10 coverage S-, 9/10 total coverage 3.3.1.5 Precipitation Type Precipitation type is determined by computer model. Reportable types are: AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-46 ### Page 81 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • Rain (R ) • Rain shower (RW ) • Snow (S) • Snow shower (SW ) • Thunderstorm ( T) Multiple precipitation types can be reported within a configuration. 3.3.1.6 Precipitation Intensity Four precipitation intensities can be reported as shown in table 3-11. Table 3-11. SD/ROB Reportable Intensities Symbol Intensity dBZ - Light 0-29 (no entry) Moderate 30-40 + Heavy 41-45 ++ Heavy 46-49 X Extreme 50-56 XX Extreme 57 or more Examples: 7R- 7/10 coverage of light rain 3R-6S 3/10 coverage light rain, 6/10 coverage moderate snow, 9/10 total coverage 2TRWX4R- 2/10 coverage thunderstorms, extreme rain showers , 4/10 coverage light rain, 6/10 total coverage 3.3.1.7 Location An area is coded with two end points and a width that defines a rectangle. Each end point is defined by an azimuth and range (AZRAN). A line is also coded with two end points and a width that defines a rectangle. Each end point is defined by an AZRAN. A cell is coded as a single point with a diameter (D). This point is defined by an AZRAN. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-47 ### Page 82 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 3-13. SD/ROB AREA, Line (LN), and CELL Location Examples The “+” denotes the radar location. 3.3.1.8 Maximum Top Maximum top (MT or MTS) denotes the altitude and location of the top of the highest precipitation echo. All radar heights are estimates and assume standard atmosphere conditions and, thus, standard radar wave propagation. MT denotes radar data alone was used to determine the maximum top. MTS denotes both satellite and radar data were used to estimate the maximum top. The maximum top is coded as a three-digit number in hundreds of feet MSL. Location is coded as an azimuth and range (AZRAN) relative to the radar site. If echo tops are uniform in altitude, the letter “U” precedes the altitude with no AZRAN provided. Examples: MT 150 19/32 Maximum top 15,000 feet MSL at 19 degrees, 32 nautical miles MT 340 182/98 Maximum top 34,000 feet MSL at 182 degrees, 98 nautical miles MTS 520 5/121 Maximum top with satellite data 52,000 feet MSL at 5 degrees, 121 nautical miles 3.3.1.9 Cell Movement Cell movement is the average motion of all the cells within a configuration. It is coded in the following format: the cell movement group is indicated by the letter C followed by four digits. The first two digits represent the direction the cell(s) is (are) moving from in tens of degrees referenced to true north. The last two digits represent the speed of the configuration in knots. Movement of areas and lines is not coded. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-48 ### Page 83 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Examples: C0209 Cell movement from 20 degrees at 9 knots C2043 Cell movement from 200 degrees at 43 knots C3616 Cell movement from 360 degrees at 16 knots 3.3.1.10 Remarks Remarks contain information about the radar’s status and type of report. Currently, all weather radar reports are automated. Table 3-12. Weather Radar Report Remarks and Meaning REMARK MEANING PPINE Equipment normal and operating, but no echoes observed PPINA Observation not available PPIOM Radar out for maintenance AUTO Report derived from an automated weather radar 3.3.1.11 Digital Section The information contained in the digital section is used primarily to create the Radar Summary Chart. However, with the proper grid overlay chart for the corresponding radar site, the digital section code can also be used to determine precipitation location and intensity. (See Figure 3- 11 for an example of a digital code plotted from the Oklahoma City, Oklahoma, Weather Radar Report.) Each digit represents the maximum precipitation intensity found within a grid box as determined by the weather radar. Light intensity is denoted by a 1, 2 is for moderate, 3 and 4 is for heavy, 5 and 6 is used for extreme precipitation. These digits were once commonly referred to as VIP levels because precipitation intensity, and therefore the digit, was derived using a video integrator processor (VIP). Whereas the old WSR-57 and WSR-74 weather radar video integrator processors displayed six data levels, the WSR-88D weather radar displays sixteen data levels. The data levels are still converted back to six levels for use in the Radar Weather Report. To avoid confusion, the term VIP should no longer be used to describe precipitation intensity. For example, if a grid box is coded with the number 2, it would be described as “moderate” precipitation,” not “VIP 2” or “level 2” precipitation. A grid box is identified by two letters. The first represents the row in which the box is found and the second letter represents the column. For example MO1 identifies the box located in row M and column O as containing light precipitation. A code of MO1234 indicates precipitation in four consecutive boxes in the same row. Working from left to right: box MO = 1, box MP = 2, MQ = 3, and box MR = 4. A Weather Radar Report contains data about precipitation echoes only. It does not contain information about important non-precipitation echoes such as clouds, fronts, dust, etc., which can be detected by weather radar under certain circumstances. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-49 ### Page 84 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) HQ N HI HJ HM • HP HQ HR JG IP JK JL KG JM JN JO JP KJ KK KL JS KN КР LK LM I KS MG LM UN LO LP **MI MJ MK ML ILO LR** AMILX MN MO MP NI INJ NK NL NM 1 MR †MS /Og NN I NO INP au 1 NQ INR >G PI IPJ PK /PL OL OM ON 100 /OP 0Q OR ros ан PN 4 PO PP IPQ ак PS 1 PT ам ON RI OR RK AL RM **ISH SI SJ RP RO RS RT SM SN** **ITH TI TJ TK TL TM S SP SQ SA SS ST** I TO TP Figure 3-14. SD/ROB Digital Section Information Plotted on a PPI Grid Overlay Example (See Table 3-11 for Intensity Level Codes 1 through 6.) 3.3.2 Examples GRB 1135 AREA 4TRW+ 9/101 133/76 54W MT 310 45/47 C2428 AUTO Green Bay, Wisconsin, automated Radar Weather Report at 1135 UTC. An area of echoes, 4/10 coverage, contained thunderstorms and heavy rain showers. Area is defined by points (referenced from GRB radar site) at 9 degrees, 101 nautical miles and 133 degrees, 76 nautical miles. These points, plotted on a map and connected with a straight line, define the center line of the echo pattern. The width of the area was 54 nautical miles; i.e., 27 nautical miles either side of the center line. Maximum top was 31,000 feet MSL located at 45 degrees and 47 nautical miles from Green Bay. Cell movement was from 240 degrees at 28 knots. ICT 1935 IN 9TRWX 274/84 216/93 22W MTS 440 260/48 C2131 AUTO Wichita, Kansas, automated Radar Weather Report at 1935 UTC. A line of echoes, 9/10 coverage, contained thunderstorm with intense rain showers. The center of the line extended AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-50 ### Page 85 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) from 274 degrees, 84 nautical miles to 216 degrees, 93 nautical miles. The line was 22 nautical miles wide. To display graphically, plot the center points on a map and connect the points with a straight line; then plot the width. Since the thunderstorm line was 22 nautical miles wide, it extended 11 nautical miles either side of your plotted line. The maximum top is 44,000 feet MSL at 260 degrees, 48 nautical miles from Wichita. Cell movement was from 210 degrees at 31 knots. **GGW 1135 AREA 3S- 95/129 154/81 34W MT 100 130/49 0805 AUTO** Glasgow, Montana, automated Radar Weather Report at 1135 UTC. An area, 3/10 coverage, of light snow. The area’s centerline extended from points at 95 degrees, 129 nautical miles to 154 degrees, 81 nautical miles from Glasgow. The area was 34 nautical miles wide. The maximum top was 10,000 feet MSL, at 130 degrees, 49 nautical miles from Glasgow. Cell movement was from 80 degrees at 5 knots. JGX 2235 AREA 2TRW++6R- 67/130 308/45 106W MT 380 66/54 C2038 AUTO Atlanta, Georgia, automated Radar Weather Report at 2235 UTC. An area of echoes, total coverage 8/10, with 2/10 of thunderstorms with very heavy rain showers and 6/10 coverage of light rain (This suggests that the thunderstorms were embedded in an area of light rain). The area was 53 nautical miles either side of the line defined by the two points, 67 degrees, 130 nautical miles and 308 degrees, 45 nautical miles from Atlanta. Maximum top was at 38,000 feet and was located on the 66 degree radial of JGX at 54 nautical miles. Cell movement was from 200 degrees at 38 knots. HKM 0235 CELL TRW+ 19/22 D5 MT 270 18/23 C0414 AUTO Kohala, Hawaii, automated Radar Weather Report at 0235 UTC. A cell, containing thunderstorms with very heavy rain showers, 5 miles in diameter, was located 19 degrees, 22 nautical miles from Kohala. Maximum top was 27,000 feet located at 18 degrees, 23 nautical miles from Kohala. Movement was from 40 degrees at 14 knots. **TLX 0435 PPINE AUTO** Oklahoma City, Oklahoma, automated Radar Weather Report at 0435 UTC, detected no echoes. AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-51 ### Page 86 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) KIMSK **KGGW OKMVX KDI** OKIFX OKBIS KELX KABE O КИРУ KGRB O KMAX KUDX KARY KRIW →KIE ADITY C КОСх KBB X KIŘx КСУУ кадк KOAX O OKRCE OKILN KRLX KDAX *KUEX ILLO KFTGO OKEAX KICK KPUX O KE SX KDDCO ÖKIT ÖKSEF *EMEX KRAI OKVTX KEYXO KNKX KIWA KF SX ' KABX KPDE OKLBB HUN KIng -OKFDR CATLE OKSRX KLZK KGWO KNOA KHIS KBMX RESP OKCA Cas -KYUX кНіх KIGX KEMY OKFWS ÖESHY КРОЕ KJAN KE OXO KÅIT KGRK O KLCH' киХО KDEX KEWE PAPD Figure 3-15. WSR-88D Weather Radar Network Sites AC 00-45F, CHG 2 Section 3: Observed Text Products Page 3-52 ### Page 87 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4 RADAR AND SATELLITE IMAGERY 4.1 Radar 4.1.1 Description Radar images are graphical displays of precipitation and non-precipitation targets detected by weather radar. WSR-88D Doppler radar displays these targets on a variety of products which can be found on the internet on the National Weather Service (NWS) Doppler Radar Images web site at: http://radar.weather.gov/ridge/ 4.1.2 Modes of Operation The WSR-88D Doppler radar has two operational modes, Clear Air and Precipitation. 4.1.2.1 Clear Air Mode In Clear Air Mode, the radar is in its most sensitive operation. This mode has the slowest antenna rotation rate which permits the radar to sample the atmosphere longer. This slower sampling increases the radar's sensitivity and ability to detect smaller objects in the atmosphere. The term "clear air" does not imply "no-precipitation" mode. Even in Clear Air Mode, the WSR- 88D can detect light, stratiform precipitation (e.g., snow) due to the increased sensitivity. Many of the radar returns in Clear Air Mode are airborne dust and particulate matter. The WSR- 88D images are updated every 10 minutes when operating in this mode. 4.1.2.2 Precipitation Mode Precipitation targets typically provide stronger return signals to the radar than non-precipitation targets. Therefore, the WSR-88D is operated in Precipitation Mode when precipitation is present although some non-precipitation echoes can still be detected in this operating mode. The faster rotation of the WSR-88D in Precipitation Mode allows images to update at a faster rate approximately every 4 to 6 minutes. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-1 ### Page 88 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4.1.3 Echo Intensities Clear Air Mode Precipitation Mode Figure 4-1. WSR-88D Weather Radar Echo Intensity Legend The colors on radar images represent different echo reflectivities (intensities) measured in dBZ (decibels of Z). The dBZ values increase based on the strength of the return signal from targets in the atmosphere. Each reflectivity image includes a color scale that represents a correlation between reflectivity value and color on the radar image. Figure 4-1 depicts these correlations for both Clear Air and Precipitation Mode. For Clear Air Mode the scale ranges from -28 to +28 dBZ, for Precipitation Mode the scale ranges from 5 to 75 dBZ. The color on each scale remains the same in both operational modes, only the dBZ values change. The scales also include ND correlated to black which indicates no data was measured. Reflectivity is correlated to intensity of precipitation. For example, in Precipitation Mode, when the dBZ value reaches 15, light precipitation is present. The higher the indicated reflectivity value, the higher the rainfall rate. The interpretation of reflectivity values is the same for both Clear Air and Precipitation Modes. Reflectivity is also correlated with intensity terminology (phraseology) for air traffic control purposes. Table 4-1 defines this correlation. Table 4-1. WSR-88D Weather Radar Precipitation Intensity Terminology Reflectivity (dBZ) Ranges Weather Radar Echo Intensity Terminology <30 dBZ Light 30-40 dBZ Moderate >40-50 dBZ Heavy 50+ dBZ Extreme AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-2 ### Page 89 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Values below 15 dBZ are typically associated with clouds. However, they may also be caused by atmospheric particulate matter such as dust, insects, pollen, or other phenomena. The scale cannot be used to determine the intensity of snowfall. However, snowfall rates generally increase with increasing reflectivity. 4.1.4 Products The NWS produces numerous radar products of interest to the aviation community. The next section will discuss Base Reflectivity and Composite Reflectivity both available through National Weather Service (NWS) Doppler Radar Images web site at: http://radar.weather.gov/ridge/ 4.1.4.1 Base Reflectivity Base Reflectivity is a display of both the location and intensity of reflectivity data. Base Reflectivity images encompass several different elevation angles (tilts) of the antenna. The Base Reflectivity image currently available on the ADDS website begins at the lowest tilt angle (0.5°), more specifically 0.5° above the horizon. Both a short range (Figure 4-2) and long range (Figure 4-3) image is available from the 0.5º Base Reflectivity product. The maximum range of the short range Base Reflectivity product is 124 NM from the radar location. This view will not display echoes farther than 124 NM from the radar site, although precipitation may be occurring at these greater distances. Other options to view precipitation beyond 124 NM from the radar site include selecting the long-range view which increases coverage out to 248 NM, selecting adjacent radars, or viewing a radar mosaic. Figure 4-2. WSR-88D Weather Radar Short Range (124 NM) Base Reflectivity Product Example AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-3 ### Page 90 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) DBZ Radar Image from National Weather Service: KPAH 19:03 UTC 04/29/2005 + Kankakee + Fort Wayne 75 Lamoni Peoria + Logansport + Lima -70 + Kirksville + Champaign. + Quinci Springfield talindianapolis -65 + Terre Haute -60 + Bloomington Columbia 55 50 • Evansville Louis ville 45 + Springfield Swing Green romar Blu 35 * pray con -30 lyersbun shville + Crossville 25 + Jackson + Lawrenceburg 20 + Memphis + Chattanboga HOttle Rock Horence « Hunts vine 15 + Pine Blurg!™ • Oxfort Tupela + Rome 10 + Gadsden + Columbus + Birgingham. Greenville + El Dorado + luscaloosa J IND Radar Image from National Weather Service: KPAH 19:03 UTC 04/29/2005 Figure 4-3. WSR-88D Weather Radar Long Range (248 NM) Base Reflectivity Product Example 4.1.4.1.1 Base Reflectivity Use The Base Reflectivity product can be used to determine the location of precipitation and nonprecipitation echoes, the intensity of liquid precipitation, and the general movement of precipitation when animating the image. If the echo is precipitation, the product can be used to determine if it is convective or stratiform in nature. Stratiform precipitation (Figure 4-4) has the following characteristics: • Widespread in areal coverage, • Weak reflectivity gradients, • Precipitation intensities are generally light or moderate (39 dBZ or less), • Occasionally, precipitation intensities can be stronger • Echo patterns change slowly when animating the image. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-4 ### Page 91 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-4. WSR-88D Weather Radar Stratiform Precipitation on the 0.5ºBase Reflectivity Product Example Hazards associated with stratiform precipitation include possible widespread icing above the freezing level, low ceilings and reduced visibilities. Convective precipitation (Figure 4-5) can be described using the following characteristics: Figure 4-5. WSR-88D Weather Radar Convective Precipitation on the 0.5ºBase Reflectivity Product Example y Echoes tend to form as lines or cells, y Reflectivity gradients are strong, AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-5 ### Page 92 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) y Precipitation intensities generally vary from moderate to extreme, − Occasionally precipitation intensities can be light y Echo patterns change rapidly when animating the image Numerous hazards are associated with convective precipitation. They include: turbulence, lowlevel wind shear, strong and gusty surface winds, icing above the freezing level, hail, lightning, tornadoes and localized IFR conditions with heavy precipitation. 4.1.4.1.2 Strengths of Base Reflectivity The strengths of the Base Reflectivity product include: • The location of precipitation and non-precipitation echoes is depicted, and • The intensity and movement of precipitation is relatively easy and straight forward to determine. 4.1.4.1.3 Limitations of Base Reflectivity Limitations associated with the Base Reflectivity product include: • The radar beam may overshoot targets, and • The image may be contaminated by: o Beam blockage o Ground clutter o Anomalous Propagation (AP) and o Ghosts. 4.1.4.1.3.1 Radar Beam Overshooting Radar beam overshooting may occur because the radar beam (typically the 0.5 degree slice) can be higher than the top of precipitation. This will most likely occur with stratiform precipitation and low-topped convection. For example, at a distance of 124 NM from the radar, the 0.5º Base Reflectivity radar beam is at an altitude of approximately 18,000 feet; at 248 NM the beam height is approximately 54,000 feet. Any precipitation with tops below these altitudes and distances will not be displayed on the image. Therefore, it is quite possible that precipitation may be occurring where none appears on the radar image. 4.1.4.1.3.2 Beam Blockage Beam blockage (Figure 4-6) occurs when the radar beam is blocked by terrain and is particularly predominant in mountainous terrain. This impacts both the Composite Reflectivity and Base Reflectivity images. Beam blockage is most easily seen on the 0.5º Base Reflectivity images where it appears as a pie-shaped area (or areas) perpetually void of echoes. When animating the imagery, the beam blockage area will remain clear of echoes even as precipitation and other targets pass through. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-6 ### Page 93 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-6. WSR-88D Weather Radar Beam Blockage on Base Reflectivity Product Example 4.1.4.1.3.3 Ground Clutter Ground clutter (Figure 4-8) is radar echoes returns from trees, buildings, or other objects on the ground. It appears as a roughly circular region of high reflectivities at ranges close to the radar. Ground clutter appears stationary when animating images and can mask precipitation located near the radar. Most ground clutter is automatically removed from WSR-88D imagery, so typically it is does not interfere with image interpretation. Figure 4-8. WSR-88D Weather Radar Ground Clutter Example AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-7 ### Page 94 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4.1.4.1.3.4 Ghost A Ghost (Figure 4-9) is a diffused echo in apparently clear air caused by a “cloud” of point targets such as insects or by refraction returns of the radar beam in truly clear air. The latter case commonly develops at sunset due to superrefraction during the warm season. The ghost develops as an area of low reflectivity echoes (typically less than 15dBZ) near the radar site and quickly expands. When animating the imagery, the ghost echo shows little movement. Figure 4-9. WSR-88D Weather Radar Ghost Example 4.1.4.1.3.5 Angels Angels are echoes caused by a physical phenomenon not discernible by the eye at the radar site. They are usually caused by bats, birds or insects. Angels typically appear as a donutshaped echo with low reflectivity values (Figure 4-10). When animated, the echo expands and becomes more diffuse with time. Angels typically only appear only when the radar is in Clear Air Mode because of their weak reflectivity. Echoes caused by birds are typically detected in the morning when they take flight for the day. Echoes caused by bats are typically detected in the evening, when they are departing from caves. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-8 ### Page 95 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-10. WSR-88D Weather Radar Angle Example This angel was caused by bats departing Selman Bat Cave at Alabaster Caverns State Park, Oklahoma around sunset 4.1.4.1.3.6 Anomalous Propagation (AP) Anomalous propagation (AP) (Figure 4-11) is an en extended pattern of ground echoes caused by superrefraction of the radar beam. Superrefraction causes the radar beam to bend downward and strike the ground. It differs from ground clutter because it can occur anywhere within the radar’s range, not just at ranges close to the radar. AP typically appears as speckled or blotchy, high reflectivity echoes. When animating images, AP tends to “bloom up” and dissipate and has no continuity of motion. AP can sometimes be misinterpreted as thunderstorms; differentiating between to two is determined by animating images. Thunderstorms move with a smooth, continuous motion while AP appears to “bloom up” and dissipate randomly. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-9 ### Page 96 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) **BASE REFLECTIWITY** KILX - OKLAHOMA CITY, OK ANOMALOUS 05/26/2000 12:15:59 GMT PROPOGATION LAT: 35/19/58 N LON: 97/16/40 W ELEV: 1277.0 FT MODE/"CP: Д / 11 ELEV ANGLE: 0.50 ° MAX: 73 dBZ RANGE 248 NM Legend: (Category) dBZ (16) 75 (14) 70 (13) 85 (12) 60 (11) 55 ПОЛА @C01002 8888990 Figure 4-11. WSR-88D Weather Radar Anomalous Propagation (AP) Example 4.1.4.2 Composite Reflectivity Composite reflectivity is the maximum echo intensity (reflectivity) detected within a column of the atmosphere above a location. The radar scans through all of the elevation slices to determine the highest dBZ value in the vertical column (Figure 4-12) then displays that value on the product. When compared with Base Reflectivity, the Composite Reflectivity can reveal important storm structure features and intensity trends of storms. THE VALUE DISPLAYED ON THE COMPOSITE REFLECTIVITY PRODUCT IS: Figure 4-12. Creation of a Composite Reflectivity product AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-10 ### Page 97 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) The maximum range of the long range Composite Reflectivity product (Figure 4-13) is 248 NM from the radar. The "blocky" appearance of this product is due to its lower spatial resolution as it has one-fourth the resolution of the Base Reflectivity product. DBZ Radar image trom National Weather Service: КРАН 19:03 UTC 04/29/2005 + Kankakee * Fort Wayne 75 Lamoni Peoria + Logansport + Lima + Kirksville Champaign + Quincy Springfield atindianapolis L+ Tèrre Haute + Bloomington Columbia vandalia, Clinton T7+ Louisville 50 evansville tut 45 40 * Springfield wing Green 35 eat Branson 30 • Crossville 25 + Lawrenceburg Memphis 1+ Chattanooga Little Rock -Horence - Huntsvme + Pine Blurg + Oxford Tupelo + Rome + Gadsden + El Dorado Da Greenville Columbus: + Tuscaloosa J + Bimpingham INDI Radar Image from National Weather Service: КРАН 19:03 UTC 04/29/2005 Figure 4-13. WSR-88D Weather Radar Long Range (248 NM) Composite Reflectivity Product Example For a higher resolution (1.1 x 1.1 NM grid) Composite Reflectivity image, users must select the short range view (Figure 4-14). The image is less "blocky" as compared to the long range image. However, the maximum range is reduced to 124 NM from the radar location. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-11 ### Page 98 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-14. WSR-88D Weather Radar Short Range (124 NM) Composite Reflectivity Product Example 4.1.4.2.1 Composite Reflectivity Use The primary use of the Composite Reflectivity product, which offers the highest reflectivity value in a vertical column, is to determine the vertical structure of the precipitation. The image must be compared with the Base Reflectivity image to determine the vertical structure of the precipitation. Figure 4-15 includes the 0.5º Base Reflectivity and Composite Reflectivity images for the same location and period of time. In Figure 4-15, within location A, the intensity of the echoes is higher on the Composite Reflectivity image. Also, within area B, many more echoes present on the Composite Reflectivity. Since the Composite Reflectivity product displays the highest reflectivity of all elevation scans, it is detecting these higher reflectivities at some higher altitude/elevation than the Base Reflectivity product, which is sampling closer to the ground. This often occurs when precipitation and especially thunderstorms are developing. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-12 ### Page 99 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Base Reflectivity Composite Reflectivity Figure 4-15. WSR-88D Weather Radar 0.5º Base Reflectivity versus Composite Reflectivity Comparison 4.1.4.2.2 Strengths of Composite Reflectivity The primary strength of the Composite Reflectivity product is its three-dimensional view of reflectivity. The method used to determine this three-dimensional view is described in section 4.1.4.2.1. 4.1.4.2.3 Limitations of Composite Reflectivity Limitations associated with the Composite Reflectivity product include: • The radar beam may overshoot targets, and • The image may be contaminated by: o Beam blockage o Ground clutter o Anomalous Propagation (AP) and o Ghosts. 4.1.4.2.3.1 Radar Beam Overshooting Radar beam overshooting may occur because the lowest base reflectivity tilt (0.5) can be higher than the top of precipitation. This will most likely occur with stratiform precipitation and lowtopped convection. For example, at a distance of 124 NM from the radar, the radar beam is at an altitude of approximately 18,000 feet above the radar; at 248 NM the beam height is approximately 54,000 feet. Any precipitation with tops below these altitudes and distances will not be displayed on the image. Therefore, it is quite possible that precipitation may be occurring where none appears on the radar image. 4.1.4.2.3.2 Beam Blockage Beam blockage (Figure 4-6) occurs when the radar beam is blocked by terrain and is particularly predominant in mountainous terrain. This impacts both the Composite Reflectivity and Base Reflectivity images. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-13 ### Page 100 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Beam blockage is most easily seen on the 0.5º Base Reflectivity images where it appears as a pie-shaped area (or areas) perpetually void of echoes. When animating the imagery, the beam blockage area will remain clear of echoes even as precipitation and other targets pass through. 4.1.4.2.3.3 Ground Clutter Ground clutter (Figure 4-8) is radar echoes returns from trees, buildings, or other objects on the ground. It appears as a roughly circular region of high reflectivities at ranges close to the radar. Ground clutter appears stationary when animating images and can mask precipitation located near the radar. Most ground clutter is automatically removed from WSR-88D imagery, so typically it is does not interfere with image interpretation. 4.1.4.2.3.4 Ghost A Ghost (Figure 4-9) is a diffused echo in apparently clear air that is caused by a “cloud” of point targets such as insects or by refraction returns of the radar beam in truly clear air. The latter case commonly develops at sunset due to superrefraction during the warm season. The ghost develops as an area of low reflectivity echoes (typically less than 15 dBZ) near the radar site and quickly expands. When animating the imagery, the ghost echo shows little movement. 4.1.4.2.3.5 Angels Angels are echoes caused by a physical phenomenon not discernible by the eye at the radar site. They are usually causes by bats, birds or insects. Angels typically appear as a donutshaped echo with low reflectivity values (Figure 4-10). When animating, the echo expends and becomes more diffuse with time. Angels typically only appear only when the radar is in clear air mode because of their weak reflectivity. Echoes caused by birds are typically detected in the morning when they take flight for the day. Echoes caused by bats are typically detected in the evening when they take flight from caves. 4.1.4.2.3.6 Anomalous Propagation (AP) Anomalous propagation (AP) (Figure 4-11) is an en extended pattern of ground echoes caused by superrefraction of the radar beam. Superrefraction causes the radar beam to bend downward and strike the ground. It differs from ground clutter because it can occur anywhere within the radar’s range, not just at ranges close to the radar. AP typically appears as speckled or blotchy, high reflectivity echoes. When animating images, AP tends to “bloom up” and dissipate and has no continuity of motion. AP can sometimes be misinterpreted as thunderstorms; differentiating between to two is determined by animating images. Thunderstorms move with a smooth, continuous motion while AP appears to “bloom up” and dissipate randomly. 4.1.5 Radar Mosaics A radar mosaic consists of multiple single site radar images combined to produce a radar image on a regional or national scale. Regional and national mosaics can be found at the National Weather Service (NWS) Doppler Radar Images web site: http://radar.weather.gov/ridge/ The mosaics are located toward the bottom of the page. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-14 ### Page 101 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4.1.5.1 0.5º Mosaics - Contiguous U.S. and Hawaii The NWS produces a set of regional and national mosaics (Table 4-2) in the contiguous U.S. using the 124 NM 0.5º Base Reflectivity product (Figure 4-16). Table 4-2. NWS Radar Mosaic Products Pacific Northwest Pacific Southwest Upper Mississippi Valley Southern Mississippi Valley Northeast Southeast Southern Rockies Northern Rockies Southern Plains Great Lakes Low Resolution National High Resolution National Figure 4-16. Great Lakes Regional Radar Mosaic Example The most recent image from single site radars is used to create the product. Single site data older than 15 minutes from the current time of the product are excluded from the image. Therefore, data on the mosaics will be no greater than 15 minutes old. Where radar coverage overlaps, the highest dBZ value will be plotted on the image. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-15 ### Page 102 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4.1.5.2 0.5º Mosaics - Alaska The Alaskan mosaic (Figure 4-17) differs from the contiguous product in only one way: it is created using the 248 NM 0.5º Base Reflectivity single site product. Figure 4-17. Alaskan Regional Radar Mosaic Example The long range Base Reflectivity product is used because the radar sites are located at greater distances from each other. Even with the use of the long range product, many areas of Alaskan do not have radar coverage. These areas are shaded gray on Figure 4-17. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-16 ### Page 103 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 4.2 Satellite 4.2.1 Description Satellite is perhaps the single most important source of weather data worldwide, particularly over data sparse regions such as countries without organized weather data collection and the oceans. GOES satellite imagery can be found on the NWS Aviation Digital Data Service (ADDS) website at: http://adds.aviationweather.noaa.gov/satellite/. Additional satellite imagery for Alaska can be found on the Alaska Aviation Weather Unit (AAWU) website at: http://aawu.arh.noaa.gov/sat.php 4.2.2 Imagery Types Three types of satellite imagery are commonly used: Visible, infrared (IR), and water vapor. Visible imagery is available only during daylight hours. IR and water vapor imagery are available day or night. 4.2.2.1 Visible Imagery Visible imagery (Figures 4-16 and 4-17) displays reflected sunlight from the Earth’s surface, clouds, and particulate matter in the atmosphere. These images are simply black and white pictures of the Earth from space. During daylight hours, visible imagery is the most widely used image type because it has the highest resolution and approximates what is seen with the human eye. Gray shades displayed on visible imagery can be correlated with particular features. Assuming a high sun angle, thick clouds and snow will appear white, thin clouds will appear translucent gray, land appears gray, and deep bodies of water such as lakes and oceans will appear black. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-17 ### Page 104 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-18. Visible Satellite Image – U.S. Example AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-18 ### Page 105 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-19. Visible Satellite Image – Regional-Scale Example 4.2.2.1.1 Visible Image Data Legend The data legend (Figure 4-18) on a visible image displays albedo, or reflectance, expressed as a percentage. For example, an albedo of 72 means 72 percent of the sunlight which struck a feature was reflected back to space. Figure 4-20. Visible Satellite Data Legend. The gray shades (values) represent albedo or reflectance expressed as a percentage. 4.2.2.2 Infrared (IR) Imagery Infrared (IR) images (Figure 4-19 through 4-22) display temperatures of the Earth’s surface, clouds, and particulate matter. Generally speaking, the warmer an object, the more infrared energy it emits. The satellite sensor measures this energy and calibrates it to temperature using a very simple physical relationship. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-19 ### Page 106 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Clouds that are very high in the atmosphere are generally quite cold (perhaps -50°C) whereas clouds very near the earth's surface are generally quite warm (perhaps +5°C). Likewise, land may be even warmer than the lower clouds (perhaps +20°C). Those colder clouds emit much less infrared energy than the warmer clouds and the land emits more than those warm clouds. The data measured by satellite is calibrated and colorized according to the temperature. If the temperature of the atmosphere decreases with height (which is typical), cloud-top temperature can be used to roughly determine which clouds are high-level and which are low-level. When clouds are present, the temperature displayed on the infrared images is that of the tops of clouds. When clouds are not present, the temperature is that of the ground or the ocean. Figure 4-21. Infrared (Color) Satellite Image – U.S. Example The scale is in degrees Celsius. Blue/purple colors indicate colder temperatures, while orange/red colors indicate warmer temperatures. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-20 ### Page 107 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) -68 -64 60 56 52 48 44 40 E36 E32 28 524 520 518 512 08 J 0 0 8 12 16 20 24 28 Figure 4-22. Infrared (Color) Satellite Image - Regional-Scale Example The scale is in degrees Celsius. Blue/purple colors indicate colder temperatures, while orange/red colors indicate warmer temperatures. 1-39-371-351-331-31-29 -27 -25 -23-21-191-171-15-131-11-9-71- Figure 4-23. Unenhanced Infrared (black and white) Satellite Image - U.S. Example The scale is in degrees Celsius. Lighter gray shades indicate colder temperatures, while darker gray shades indicate warmer temperatures. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-21 ### Page 108 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 4-24. Unenhanced Infrared (black and white) Satellite Image – Regional- Scale Example The scale is in degrees Celsius. Lighter gray shades indicate colder temperatures, while darker gray shades indicate warmer temperatures. 4.2.2.2.1 Infrared Image Data Legends The data legend (Figure 4-23 and Figure 4-24) on an infrared image is calibrated to temperature expressed in degrees Celsius. The legend may vary based on the satellite image provider. Figure 4-25. Infrared (Color) Satellite Image Data Legend. The colors (values) represent temperature in degrees Celsius. Figure 4-26. Unenhanced Infrared (black and while) Satellite Image Data Legend. The gray shades (values) represent temperature in degrees Celsius. 4.2.3.3 Water Vapor Imagery The water vapor imagery (Figure 4-25 and Figure 4-26) displays the quantity of water vapor generally located in the middle and upper troposphere within the layer between 700 millibars (FL100) to 200 millibars (FL390). The actual numbers displayed on the water vapor images correspond to temperature in degrees Celsius. No direct relationship exists between these values and the temperatures of clouds, unlike IR imagery. Water Vapor imagery does not really "see" clouds but "sees" high-level water vapor instead. The most useful information to be gained from the water vapor images is the locations and movements of weather systems, jet streams, and thunderstorms. Another useful tidbit is aided AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-22 ### Page 109 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) by the color scale used on the images. In general, regions displayed in shades of red are VERY dry in the upper atmosphere and MAY correlate to crisp blue skies from a ground perspective. On the contrary, regions displayed in shades of blue or green are indicative of lots of high-level moisture and may also indicate cloudiness. This cloudiness could simply be high-level cirrus types or thunderstorms. That determination cannot be gained from this image by itself but could easily be determined when used in conjunction with corresponding visible and infrared satellite images. Figure 4-27. Water Vapor Satellite Image – U.S. Example The scale is in degrees Celsius. Blue/green colors indicate moisture and/or clouds in the mid/upper troposphere, while dark gray/orange/red colors indicate dry air in the mid/upper troposphere. AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-23 ### Page 110 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Section 4: Radar and Satellite Imagery Page 4-24 Figure 4-28. Water Vapor Satellite Image – Regional-Scale Example The scale is in degrees Celsius. Blue/green colors indicate moisture and/or clouds in the mid/upper troposphere, while dark gray/orange/red colors indicate dry air in the mid/upper troposphere. 4.2.3.3.1 Water Vapor Image Data Legend The data legend (Figure 4-27) on a water vapor images is calibrated to temperature expressed in degrees Celsius. The actual data values on the water vapor images are not particularly useful. Interpretation of the patterns and how they change over time is more important. The legend may vary depending on the satellite image provider. Figure 4-29. Water Vapor Satellite Image Data Legend. The colors (values) represent temperature in degrees Celsius ### Page 111 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5 GRAPHICAL OBSERVATIONS AND DERIVED PRODUCTS 5.1 Surface Analysis Charts Surface Analysis charts are analyzed charts of surface weather observations. The chart depicts the distribution of several items including sea level pressure, the positions of highs, lows, ridges, and troughs, the location and character of fronts, and the various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. Other symbols are often added depending upon the intended use of the chart. Pressure is referred to in mean sea level (MSL) on the surface analysis chart while all other elements are presented as they occur at the surface point of observation. A chart in this general form is commonly referred to as the weather map. Figure 5-1. HPC Surface Analysis Chart Example 5.1.1 Issuance Five National Weather Service (NWS) offices issue surface analysis charts: • The Hydrometeorological Prediction Center (HPC) in Camp Springs, Maryland is responsible for land areas of North America. The charts are available at o http://www.hpc.ncep.noaa.gov/html/sfc2.shtml o http://www.hpc.ncep.noaa.gov/html/avnsfc.shtml AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-1 ### Page 112 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • The Ocean Prediction Center (OPC) in Camp Spring, Maryland is responsible for the Atlantic and Pacific Oceans north of 30oN latitude. The charts are available at: o http://www.opc.ncep.noaa.gov/ • The Tropical Prediction Center (TPC) in Miami, Florida is responsible for the tropical regions of the western hemisphere south of 30oN latitude and east of 160oE longitude. The surface analysis charts are available at: o http://www.nhc.noaa.gov/marine_forecasts.shtml • The Alaskan Aviation Weather Unit (AAWU) in Anchorage, Alaska is responsible for the state of Alaska. The surface analysis chart is available at: o http://aawu.arh.noaa.gov/surface.php • The Weather Forecast Office in Honolulu, Hawaii (WFO HNL) is responsible for the tropical Pacific Ocean, south of 30oN latitude and west of 160oE longitude. The charts are available at: o http://www.prh.noaa.gov/hnl/pages/analyses.php Each office produces multiple versions of the surface analysis chart with varying formats. 5.1.2 HPC Surface Analysis Charts • The Hydrometeorological Prediction Center (HPC) in Camp Springs, Maryland is responsible for land areas of North America. The charts are available at o http://www.hpc.ncep.noaa.gov/html/sfc2.shtml o http://www.hpc.ncep.noaa.gov/html/avnsfc.shtml 5.1.2.1 Issuance The Hydrometeorological Prediction Center (HPC) issues Surface Analysis Charts for North America eight times daily (Table 5-1). Table 5-1. HPC Surface Analysis Charts Issuance Schedule Valid Time (UTC) 00 03 06 09 12 15 18 21 5.1.2.2 Analysis Symbols Figure 5-2 shows analysis symbols used on HPC surface analysis charts: AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-2 ### Page 113 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) COLD FRONT - COLD FRONTOLYSIS WARM FRONT • WARM FRONTOLYSIS **STATIONARY FRONT STATIONARY** **OCCLUDED FRONT FRONTOLYSIS** **OCCLUDED FRONTOLYSIS** **CHANGE OF FRONT TYPE** **COLD FRONTOGENESIS HIGH PRESSURE CENTER** **WARM FRONTOGENESIS LOW PRESSURE CENTER** **STATIONARY TROPICAL (TRPL) WAVE** **FRONTOGENESIS T.D.** **TROUGH (TROF) OR XXX TROPICAL DEPRESSION** **OUTFLOW BONDARY (OUTFLOW BNDRY) 6 TRPCL STORM TROPICAL STORM** **DRYLINE** **RIDGE HURCN HURRICANE** SQUALL LINE XXX Figure 5-2. HPC Surface Analysis Chart Symbols 5.1.2.3 Station Plot Models Land, ship, buoy, and C-MAN stations are plotted on the chart to aid in analyzing and interpreting the surface weather features. These plotted observations are referred to as station models. Some stations may not be plotted due to space limitations. However, all reporting stations are used in the analysis. Figure 5-3 and 5-4 contain the most commonly used station plot models used in surface analysis charts: Wind Sea-level pressure Temperature 57 107 Weather -→ • -6 56 Pressure trend (mb) Dew Point(F) Sky cover Figure 5-3. HPC Surface Analysis Chart Station Plot Model AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-3 ### Page 114 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-4. HPC Surface Analysis Chart Ship/Buoy Plot Model HPC also produces surface analysis charts specifically for the aviation community. Figure 5-5 contains the station plot model for these charts: Figure 5-5. HPC Surface Analysis Chart for Aviation Interests Station Plot Model 5.1.2.3.1 Station Identifier The format of the station identifier depends on the observing platform. • Ship -- Typically 4 or 5 characters. If 5 characters, then the fifth will usually be a digit. • Buoy -- Whether drifting or stationary, a buoy will have a 5-digit identifier. The first digit will always be a 4. • C-MAN -- Stands for Coastal-Marine Automated Network, and are usually close to coastal areas. Their identifier will appear like a 5-character ship identifier, however the 4th character will identify off which state the platform is located. • Land -- Land stations will always be 3 characters, making them easily distinguishable from ship, buoy, and C-MAN observations. 5.1.2.3.2 Temperature The air temperature is plotted in whole degrees Fahrenheit. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-4 ### Page 115 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.2.3.3 Dew Point The dew point temperature is plotted in whole degrees Fahrenheit. 5.1.2.3.4 Weather A weather symbol is plotted if, at the time of observation, precipitation is either occurring or a condition exists causing reduced visibility. Figure 5-6 contains a list of the most common weather symbols: Figure 5-6. HPC Surface Analysis Chart Common Weather Symbols A complete list of weather symbols can be found at in Appendix I. 5.1.2.3.5 Wind Wind is plotted in increments of 5 knots (kts). The wind direction is in “true” degrees and is depicted by a stem (line) pointed in the direction from which the wind is blowing. Wind speed is determined by adding the values of the flags (50kts), barbs (10kts), and half-barbs (5kts) found on the stem. If the wind is calm at the time of observation, only a single circle over the station is depicted. Figure 5-7 are some sample wind symbols: AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-5 ### Page 116 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-7. HPC Surface Analysis Chart Wind Plotting Model 5.1.2.3.6 Ceiling Ceiling is plotted in hundreds of feet above ground level. 5.1.2.3.7 Visibility Surface visibility is plotted in whole statute miles. 5.1.2.3.8 Pressure Sea-level pressure is plotted in tenths of millibars (mb), with the first two digits (generally 10 or 9) omitted. For reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample conversions between plotted and complete sea-level pressure values: 410: 1041.0 mb 103: 1010.3 mb 987: 998.7 mb 872: 987.2 mb 5.1.2.3.9 Pressure Trend The pressure trend has two components, a number and a symbol, to indicate how the sea level pressure has changed during the past three hours. The number provides the 3-hour change in tenths of millibars while the symbol provides a graphic illustration of how this change occurred. Figure 5-8 contains the meanings of the pressure trend symbols: AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-6 ### Page 117 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Continuously falling Continuously rising Falling, then steady Rising, then steady Falling before a lesser rise Falling before a greater rise Rising before a greater fall Rising before a lesser fall Steady Figure 5-8. HPC Surface Analysis Chart Pressure Trends 5.1.2.3.10 Sky Cover The approximate amount of sky cover can be determined by the circle at the center of the station plot. The amount the circle is filled reflects the amount of sky covered by clouds. Figure 5-9 contains the common cloud cover depictions: Clear catered cloud approximately 25% cloud cover (apply cinately 50% cloud cover) (apstYxinoely 75% cloud cover) Overcast Sky Obscured Sky Cover Missing Figure 5-9. HPC Surface Analysis Chart Sky Cover Symbols 5.1.2.3.11 Water Temperature Water temperature is plotted in whole degrees Fahrenheit. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-7 ### Page 118 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.2.3.12 Swell Information Swell direction, period, and height are represented in the surface observations by a 6-digit code. The first two digits represent the swell direction, the middle digits describe the swell period (in seconds), and the last two digits are the swell's height (in half meters). 090703 09 - The swell direction is from 90 degrees (i.e. it is coming from due east). 07 - The period of the swell is 7 seconds. 03 - The height of the swell is 3 half meters. 271006 27 - The swell direction is from 270 degrees (due west). 10 - The period is 10 seconds. 06 - The height of the swell is 6 half meters. 5.1.2.3.13 Wave Information Period and height of waves are represented by a 5-digit code. The first digit is always 1. The second and third digits describe the wave period (in seconds), and the final two digits give the wave height (in half meters). 10603 1 - A group identifier. The first digit will always be 1. 06 - The wave period is 6 seconds. 03 - The wave height is 3 half meters. 10515 1 - The group identifier again. 05 - The wave period is 5 seconds. 15 - Wave height is 15 half meters. In some charts by the OPC, only the wave height (in feet) is plotted. 5.1.2.4 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on surface analysis charts. 5.1.2.4.1 Isobars An isobar is a line of equal or constant pressure commonly used in the analysis of pressure patterns. On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1,032.0 mb and 992 signify 992.0 mb. METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-8 ### Page 119 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.2.4.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure located at the center of a High or Low. In general, the central pressure is the highest pressure in the center of a High and the lowest pressure at the center of a Low. The central pressure is denoted near each pressure center. A trough or an elongated area of low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of high atmospheric pressure is denoted by saw-toothed symbols. Ridges are rarely denoted on charts produced by the HPC. Tropical storms, hurricanes, and typhoons (See Figure 5-2) are low-pressure systems with their names and central pressures denoted. 5.1.2.4.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-2. The symbols on the front indicate the type of front and point in the direction toward which the front is moving. Two short lines across a front indicate a change in front type. Figure 5-10. HPC Surface Analysis Chart – North America Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-9 ### Page 120 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-11. HPC Surface Analysis Chart - Contiguous U.S. Example Figure 5-12. HPC Surface Analysis Chart - Northeast U.S. Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-10 ### Page 121 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-13. HPC Surface Analysis Chart for Aviation Interests – Contiguous U.S. Example Figure 5-14. HPC Surface Analysis Chart for Aviation Interests – South central U.S. Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-11 ### Page 122 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.3 OPC and WFO Honolulu Surface Analysis Charts The Ocean Prediction Center (OPC) in Camp Spring, Maryland is responsible for the Atlantic and Pacific Oceans north of 30°N latitude. The charts are found at: • http://www.opc.ncep.noaa.gov/ The Weather Forecast Office in Honolulu, Hawaii (WFO HNL) is responsible for the tropical Pacific Ocean, south of 30°N latitude and west of 160°E longitude. The charts are found at: • http://www.prh.noaa.gov/hnl/pages/analyses.php 5.1.3.1 Issuance The Ocean Prediction Center (OPC) produces surface analysis charts for the Atlantic and Pacific Oceans north of 30°N latitude four times daily (Table 5-2). The Weather Forecast Office in Honolulu, Hawaii (WFO HNL) issues surface analysis charts for the tropical Pacific Ocean, south of 30°N latitude and west of 160°E longitude four times daily. Surface analysis charts for the North Pacific are jointly issued by both offices. Table 5-2. OPC and WFO Honolulu Surface Analysis Charts Issuance Schedule UTC 00 06 12 18 5.1.3.2 Analysis Symbols Figure 5-15 shows analysis symbols used on OPC and WFO HNL surface analysis charts. H 30 • MODERATE ICING TEXT ABBREVIATIONS: 1024 24HR HIGH PRES MOVMI O HEAVY ICING AND PRES IN MBS STORM = 48-63 KT GALE = 34-47 KT HIGH PRES CENTER WIND BARBS: HURCN => 64 KT WITH PRES IN MBS = 5 кТ KI = KNOTS, G = GUSTS 99 HR = HOUR 10 KT MBS = MILLIBARS LOW PRES 996 CENTER AND PRES 24HR LOW PRES MOVMT IN MBS EFF = 20 КТ - 15 KT HURCN = HURRICANE PRES = PRESSURE DSIPT = DISSIPATED WITH PRES IN MBS = 25 KT SINRY = STATIONARY = 35 KT WKNG = WEAKENING COLD FRONT = 50 кТ RPDLY = RAPIDLY FRMG = FORMING = 60 KT MOVG = MOVING WARM FRONT ALL • = 65 KT AlL = 75 KT SINRY FRONT L = 100 KT OCCLUDED FRONT LAL =110 KT COMB = COMBINING DCRS = DECREASING RIDGE LIL = 120 KT INCR = INCREASING INTSFYG = INTENSIFYING ) HURCN TROF • HURCN SOUTHERN HEMISPHERE PSN = POSITION Q TRPCL STORM I TROPICAL DEPRESSION < TROPICAL DISTURBANCE Figure 5-15. OPC and WFO HNL Surface Analysis Chart Symbols AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-12 ### Page 123 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-16. WFO HNL Surface Analysis Chart – North Pacific Example 5.1.3.3 Wave Information Period and height of waves are represented by a 5-digit code. The first digit is always 1. The second and third digits describe the wave period (in seconds), and the final two digits give the wave height (in half meters). Below are two examples: 10603 1 - A group identifier. The first digit will always be 1. 06 - The wave period is 6 seconds. 03 - The wave height is 3 half meters. 10515 1 - The group identifier again. 05 - The wave period is 5 seconds. 15 - Wave height is 15 half meters. In certain charts by the OPC, only the wave height (in feet) is plotted. 5.1.3.4 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on the surface analysis charts. 5.1.3.4.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-13 ### Page 124 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1,032.0 mb and 992 signify 992.0 mb. METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required. 5.1.3.4.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low -- the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. Tropical storms, hurricanes, and typhoons (See Figure 5-15) are low-pressure systems with their names and central pressures denoted. A trough or an elongated area of low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of high atmospheric pressure is denoted with saw-toothed symbols. Ridges are rarely denoted on charts produced by the HPC. 5.1.3.4.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-15. The symbols on the front indicate the type of front and point in the direction toward which the front is moving. Two short lines across a front indicate a change in front type. 5.1.4 TPC Surface Analysis Charts The Tropical Prediction Center (TPC) in Miami, Florida is responsible for the tropical regions of the western hemisphere south of 30oN latitude and east of 160oE longitude. The surface analysis chart is located at: • http://www.nhc.noaa.gov/marine_forecasts.shtml 5.1.4.1 Issuance The Tropical Prediction Center (TPC) issues Surface Analysis Charts for tropical regions of the western hemisphere south of 30oN latitude and east of 160oE longitude four times a day (Table 5-3). Table 5-3. TPC Surface Analysis Charts Issuance Schedule Valid Time (UTC) 00 06 12 18 5.1.4.2 Analysis Symbols Figure 5-17 shows analysis symbols used on TPC surface analysis charts. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-14 ### Page 125 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) H1024 CENTER OF HIGH PRES ITH PRES IN MILLIBARS TRPCL × 999 WITH PRES IN MILLIBARS TRPCL DEPRESSION CENTER OF LOW PRES STORM (IS) L 10 KI 5 KT COLD FRONT • HURRICANE (HRON) L L 15 KT 20 KT Ш 25 КТ WARM FRONT P CONVECTION We- 35 KT GALE OR TRPCL STORM STATIONARY FRONT TRPCL - 50 KT STORM WAVE Ale 74 KT HRCN **OCCLUDED FRONT TEXT ABBREVIATIONS M 105 KT DRY LN KT KNOTS 24 HR HIGH PRES** **FT FEET MOVEMENT** **SQUALL LN NM NAUTICAL MILES** **GI GUSTS** **TROF LN HRCN - HURRICANE TRPCI- TROPICAL 24 HR LOW PRES** **PRES - PRESSURE MOVEMENT** **RIDGE AXIS TROF - TROUGH LINE** **MOV MOVING** STNR - STATIONARY Figure 5-17. TPC Surface Analysis Chart Symbols SON 04 1026 1826-21 STHRY 3ON 20 TROF 1016 20 08 12 21.4N 11. IPC PSN *120KT 994 OITEZ- N 35. 34 0900 T MOYE 1955КГ 6 5k 5N los . 16 14025 . 130W 120W . 110W. 100W . 90W. SOW 16 10y 16 GOH 50W 3OW 20W 20;4! 06Z TROPICAL SURFACE ANALYSIS 2004 TROPICAL PREDICTION CENTER ISSUED: 17 SCALLOP LINES MIAMI, THUNDERSTORMS: COLLABORATING CENTERS: TAFB ANALYST: FORMOSA TPC OPC НРС HF0 Figure 5-18. TPC Tropical Surface Analysis Chart Example 5.1.4.2.1 Wind Wind is plotted in increments of 5 knots (kts). The wind direction is in "true" degrees and is depicted by a stem (line) pointed in the direction from which the wind is blowing. The wind speed is determined by adding up the value of the flags (50 kts), lines (10 kts), and half-lines (5 kts), each of which has the following individual values: AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-15 ### Page 126 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) A single circle over the station with no wind symbol indicates a calm wind. Figure 5-19 shows some sample wind symbols: Figure 5-19: TPC Surface Analysis Chart Wind Plotting Model 5.1.4.3 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on the surface analysis charts. 5.1.4.3.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns. On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1,032.0 mb and 992 signify 992.0 mb. METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required. 5.1.4.3.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low -- the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. Tropical storms, hurricanes, and AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-16 ### Page 127 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) typhoons (See Figure 5-17) are low-pressure systems with their names and central pressures denoted. A trough or an elongated area of low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of high atmospheric pressure is denoted by saw-toothed symbols. Ridges are rarely denoted on charts produced by the TPC. 5.1.4.3.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-17. The symbols on the front indicate the type of front and point in the direction toward which the front is moving. Two short lines across a front indicate a change in front type. 5.1.5 Unified Surface Analysis Chart The Unified Surface Analysis Chart is a composite of all the surface analysis charts produced by HPC, OPC, TPC and WFO Honolulu. It contains an analysis of isobars, pressure systems and fronts. 5.1.5.1 Issuance The chart is issued four times daily by the OPC (see Table 5-4). Table 5-4. Unified Surface Analysis Chart Issuance Schedule Valid Time (UTC) 00 06 12 18 Figure 5-20. Unified Surface Analysis Chart Example 5.1.5.2 Analysis Symbols Figure 5-21 shows analysis symbols used on the Unified Surface Analysis charts. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-17 ### Page 128 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-21. Unified Surface Analysis Chart Symbols 5.1.5.3 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on the surface analysis charts. 5.1.5.3.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns. On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1032.0 mb and 992 signify 992.0 mb. METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required. 5.1.5.3.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low -- the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. Tropical storms, hurricanes, and typhoons (See Figure 5-21) are low-pressure systems with their names and central pressures denoted. On a Surface Analysis Chart, a trough is an elongated area of relatively low atmospheric pressure, while a ridge is an elongated area of relatively high atmospheric pressure. Troughs are denoted by dashed lines and identified with the word TROF. Ridges are denoted by sawtoothed symbols. Ridges are rarely denoted on charts produced by the HPC. 5.1.5.3.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-21. The symbols on the front indicate the type of front and point in the direction toward which the front is moving. Two short lines across a front indicate a change in front type. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-18 ### Page 129 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.6 AAWU Surface Charts The Alaskan Aviation Weather Unit (AAWU) in Anchorage, Alaska is responsible for the state of Alaska. The surface analysis chart is located at: • http://aawu.arh.noaa.gov/surtace.php 5.1.6.1 Issuance The AAWU issues Surface Analysis Charts 4 times daily for the state of Alaska. The valid times are shown in Table 5-5. Table 5-5. AAWU Surface Analysis Issuance Schedule Valid Time 00 06 12 18 (UTC) 5.1.6.2 Analysis Symbols The symbols (Figure 5-22) used on the Alaskan Surface Analysis Chart are similar to those found on the HPC Surface Analysis chart. However, since the Alaskan Surface Analysis chart is in black and white all of the symbols are black and white as well. A Key to Symbols used on the AAWU Graphic Products - Cold Front H 1032 - High Pressure Center Pressure in millibars - Warm Front L 988 - Low Pressure Center - Occluded Front Pressure in millibars - Stationary Front - Occasional or greater - Trough Precipitation - Ridge - Fog - Freezing Rain * - Mixed Rain/Snow - Haze - Freezing Drizzle - Rain Showers - Smoke - Light Icing - Snow Showers ‡→ - Drifting Snow - Moderate Icing - Rain/Snow Showers - Sandstorm - Severe Icing K - Thunderstorm • - Drizzle * - Snow A - Light Turbulence • - Rain › - Ice Crystals A - Moderate Turbulence A - Ice Pellets A - Severe Turbulence Figure 5-22. AAWU Surface Analysis Chart Symbols AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-19 ### Page 130 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-23. AAWU Alaskan Surface Chart Example 5.1.6.3 Station Plot Models Land, ship, buoy, and C-MAN stations are plotted on the chart to aid in analyzing and interpreting the surface weather features. These plotted observations are referred to as station models. Some stations may not be plotted due to space limitations. However, all reporting stations are used in the analysis. Figures 5-24 and 5-25 show the most commonly used station plot models used in surface analysis charts. Figure 5-24. AAWU Surface Analysis Chart Station Plot Model AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-20 ### Page 131 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-25. AAWU Surface Analysis Chart Ship/buoy Plot Model 5.1.6.3.1 Station Identifier The format of the station identifier depends on the observing platform. • Ship -- Typically 4 or 5 characters. If 5 characters, then the fifth will usually be a digit. • Buoy -- Whether drifting or stationary, a buoy will have a 5-digit identifier. The first digit will always be a 4. • C-MAN -- Stands for Coastal-Marine Automated Network, and are usually close to coastal areas. Their identifier will appear like a 5-character ship identifier, however the 4th character will identify off which state the platform is located. • Land -- Land stations will always be 3 characters, making them easily distinguishable from ship, buoy, and C-MAN observations. 5.1.6.3.2 Temperature Air temperature is plotted in whole degrees Celsius on large-scale charts. Hourly surface charts may have temperatures using whole degrees Fahrenheit. 5.1.6.3.3 Dew Point Dew point temperature is plotted in whole degrees Celsius on large-scale charts. Hourly surface charts may have dew point temperatures using whole degrees Fahrenheit. 5.1.6.3.4 Wind Wind is plotted in increments of 5 knots (kts). The wind direction is in “true” degrees and is depicted by a stem (line) pointed in the direction from which the wind is blowing. Wind speed is determined by adding the values of the flags (50 kts), barbs (10kts), and half barbs (5 kts) found on the stem. A single circle over the station with no wind symbol indicates a calm wind. Figure 5-26 shows some sample wind symbols. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-21 ### Page 132 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-26: AAWU Surface Analysis Chart Wind Plotting Model 5.1.6.3.5 Ceiling Ceiling is plotted in hundreds of feet above ground level. 5.1.6.3.6 Visibility Surface visibility is plotted in whole statute miles. 5.1.6.3.7 Pressure Sea-level pressure is plotted in tenths of millibars (mb), with the first two digits omitted (generally a 10 or 9). For reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample conversions between plotted and complete sea-level pressure values: 410: 1041.0 mb 103: 1010.3 mb 987: 998.7 mb 872: 987.2 mb 5.1.6.3.8 Pressure Trend The pressure trend has two components, a number and symbol, to indicate how the sea-level pressure has changed during the past three hours. The number provides the 3-hour change in tenths of millibars, while the symbol provides a graphic illustration of how this change occurred. Figure 5-27 shows the meanings of the pressure trend symbols. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-22 ### Page 133 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Continuously falling Continuously rising Falling, then steady Rising, then steady Falling before a lesser rise Falling before a greater rise 1 Rising before a greater fall Rising before a lesser fall Steady Figure 5-27. AAWU Surface Analysis Chart Pressure Trends 5.1.6.3.9 Sky Cover The approximate amount of sky cover can be determined by the circle at the center of the station plot. The amount the circle is filled reflects the amount of sky covered by clouds. Figure 5-28 shows the common cloud cover depictions: Clear Scattered cloud: (approximately 25% cloud cover (apply sinatly 50% cloud cover) (apst xinately 75% cloud cover) Overcast Sky Obscured Sky Cover Missing Figure 5-28. AAWU Surface Analysis Chart Sky Cover Symbols 5.1.6.3.10 Water Temperature Water temperature is plotted in whole degrees Fahrenheit. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-23 ### Page 134 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.1.6.3.11 Swell Information Swell direction, period, and height are represented in the surface observations by a 6-digit code. The first two digits represent the swell direction, the middle digits describe the swell period (in seconds), and the last two digits are the swell's height (in half meters). 090703 09 - The swell direction is from 90 degrees (i.e. it is coming from due east). 07 - The period of the swell is 7 seconds. 03 - The height of the swell is 3 half meters. 271006 27 - The swell direction is from 270 degrees (due west). 10 - The period is 10 seconds. 06 - The height of the swell is 6 half meters. 5.1.6.3.12 Wave Information The period and height of waves are represented by a 5-digit code. The first digit is always 1. The second and third digits describe the wave period (in seconds), and the final two digits give the wave height (in half meters). Below are two examples: 10603 1 - A group identifier. The first digit will always be 1. 06 - The wave period is 6 seconds. 03 - The wave height is 3 half meters. 10515 1 - The group identifier again. 05 - The wave period is 5 seconds. 15 - Wave height is 15 half meters. 5.1.6.4 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on surface analysis charts. 5.1.6.4.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns. On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1032.0 mb and 992 signify 992.0 mb. METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required. 5.1.6.4.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmosphere pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low – the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-24 ### Page 135 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) A trough or an elongated area of relatively low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of relatively high atmospheric pressure is denoted by saw-toothed symbols. Ridges are rarely denoted on charts produced by the AAWU. 5.1.6.4.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-22. The symbols on the front indicate the type of front and point in the direction toward which the front is moving. Two short lines across a front indicate a change in front type. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-25 ### Page 136 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.2 Constant Pressure Charts Constant pressure charts are maps of selected conditions along specified constant pressure surfaces (pressure altitudes) and depict observed weather. Constant pressure charts help to determine the three-dimensional aspect of depicted pressure systems. Each chart provides a plan-projection view at a specified pressure altitude. Figure 5-29. Constant Pressure Chart Example 5.2.1 Issuance Constant pressure charts are issued twice per day from observed data obtained at 00Z and 12Z. Charts are available at the NWS Fax Chart web site at: http://weather.noaa.gov/fax/barotrop.shtml. 5.2.2 Observational Data Observational data is plotted according to priority with some data deleted to prevent overlap. The retention priority is: AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-26 ### Page 137 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) y Radiosonde observations (see Figure 5-30) y Weather reconnaissance aircraft observations y Aircraft observations on-time and on-level y Aircraft observations off-time or off-level y Satellite wind estimates Many other data sources are used in the analysis but are not plotted. These include: y Ships y Buoys y Tide gauges y Wind profilers y WSR-88D weather radar VAD wind profile s y Satellite sounder Figure 5-30. U.S. Radiosonde Network AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-27 ### Page 138 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 5-6 Features of Constant Pressure Charts Height Plot Decoding Examples of Height Plotting Constant Pressure Chart Pressure Altitude (MSL) Isotachs Contour Interval (meters) Prefix Suffix Plotted Height (meters, MSL) 850MB 5,000 ft 1,500 m No 30 m 1 - 530 1,530 m 700MB 10,000 ft 3,000 m No 30 m 2 or 3* - 180 3,180 m 500MB 18,000 ft 5,500 m No 60 m - 0 582 5,820 m 300MB 30,000 ft 9,000 m Yes 120 m - 0 948 9,480 m 200MB 39,000 ft 12,000 m Yes 120 m 1 0 164 11,640 m Note: Pressure altitudes are rounded to the nearest 1,000 for feet and 500 for meters. * Prefix a “2” or “3,” whichever brings the height closer to 3,000 meters. Table 5-7. Constant Pressure Chart Plotting Models Radiosonde Reconnaissanc e Aircraft (RECCO) Aircraft Report (AIREP) Satellite Wind Estimate **SYMBOL MEANING** Wind plotted in standard notation. The stem points in the direction from which the wind is blowing plotted to 36 compass points, relative to true north. Wind speed is denoted by a combination of flags (50 knots), barbs (10 knots), and half barbs (5 knots). TT Temperature rounded to the nearest whole degree Celsius, with minus sign prefixed if negative. hhh Height of the constant pressure surface in meters MSL. See the Table 5-8 to see how each chart abbreviates height. PaPaPa Pressure altitude in hundreds of feet MSL. DD Temperature-dew point spread (depression of the dew point temperature) rounded to the nearest whole degree Celsius. When DD is less than or equal to 5 degrees Celsius, the station circle is darkened so a region of high moisture content will stand out. If DD is greater than 5 degrees Celsius, the station circle is not shaded. If the DD is too large to measure, an X is plotted. For RECCO reports, DD will be missing when the temperature is colder than -41oC. R Reconnaissance aircraft type. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-28 ### Page 139 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 5-8. Radiosonde Plotting Model Examples Plotting Model 850MB 700MB 500MB 300MB 200MB Wind* 190o/20 kt 190o/25 kt 270o/15 kt 240o/70 kt 250o/115 kt TT Temperature 20oC 8 oC -11 oC -36 oC -56 oC hhh Height 1,504 m 3,156 m 5,820 m 9,560 m 12,140 m DD Temperature -Dew Point Spread 5oC 6 oC Too dry to measure 21oC 7 oC hchc Height Change -10 m -20 m +10 m -50 m -20 m * Wind direction assumes that north is at the top of the page. Latitude and longitude lines, as well as other geographical references, must be used to determine actual compass direction. 5.2.3 Analyses All constant pressure charts contain analyses of height and temperature. Selected charts have an analysis of wind speed as well. 5.2.3.1 Height Heights are analyzed with contours. Contours are lines of constant height in MSL and are used to map height variations of constant pressure surfaces. They identify and characterize pressure systems on constant pressure charts. Contours are drawn as solid lines labeled with 3-digit numbers in decameters. Intervals at which the contours are drawn at: 30 meters for the 850 mb and 700 mb charts, 60 meters for the 500-mb chart, and 120 meters for the 300-mb and 200-mb charts. The location of a High or Low is marked with a 9 symbol together with a larger H or L, and the central value in decameters printed under the center location. Contour gradient is the amount of height change over a specified horizontal distance. Gradients identify slopes of constant pressure surfaces that fluctuate in altitude. Strong gradients are denoted by closely-spaced contours which identify steep slopes. Weak gradients are denoted by widely-spaced contours which identify shallow slopes. Wind speeds are directly proportional to contour gradients. Faster wind speeds are associated with strong contour gradients and slower wind speeds are associated with weak contour gradients. In mountainous areas, winds are often variable on constant pressure charts with altitudes near terrain elevation due to friction. 5.2.3.2 Temperature Temperature is analyzed with isotherms which are lines of constant temperature. They are drawn as long dashed lines at intervals of 5° Celsius. They are given a two-digit label in whole degrees Celsius and are preceded with a + (positive) or – (negative) sign. The zero degree isotherm denotes the freezing level. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-29 ### Page 140 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Temperature gradient is the amount of temperature change over a specified distance. Isotherm gradients identify the magnitude of temperature variations. Strong gradients are denoted by closely spaced isotherms and identify large temperature variations. Weak gradients are denoted by loosely spaced isotherms and identify small temperature variations. 5.2.3.3 Wind Speed Wind speed is analyzed with isotachs. Isotachs are lines of constant wind speed. They are drawn on the 300-mb and 200-mb charts with short-dashed lines at 20-knot intervals beginning with10 knots. They are labeled with a two- or three-digit number followed by a K for knots. Regions of high wind speeds are highlighted by alternate bands of shading and no-shading at 40-knot intervals beginning at 70 knots. A jet stream axis is the axis of maximum wind speed in a jet stream. Jet axes are not explicitly indicated, but their positions can be inferred from the isotach pattern and plotted winds. 5.2.3.4 Use Constant pressure charts are used to provide an overview of selected observed weather conditions at specified pressure altitudes. Pressure patterns cause and characterize much of the weather. Typically, lows and troughs are associated with bad weather, clouds and precipitation, while highs and ridges are associated with good weather. Table 5-9. Reconnaissance Aircraft (RECCO) Plotting Model Examples Plotting Model 850MB 700MB 500MB 300MB 200MB Wind* 150o/90 kt 130o/35 kt 180o /60 kt 240o/30 kt 110o/30 kt TT Temperature 19oC 9 oC -5 oC -28 oC -53 oC hhh Height 1,366 m 3,146 m 5,800 m 9,660 m 12,420 m DD Temperature -Dew Point Spread 1oC 1 oC 2 oC 3 oC Missing R RECCO Type AA329A AA921A AA923A AA924A AA916A * Wind direction assumes that north is at the top of the page. Latitude and longitude lines, as well as other geographical references, must be used to determine actual compass direction. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-30 ### Page 141 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 5-10. Aircraft Report (AIREP) Plotting Model Examples Plotting Model 850MB 700MB 500MB 300MB 200MB Wind* 20 o/10 kt Light and Variable 300 o/30 kt 190 o/5 kt 290o/50 kt TT Temperature -5oC 12 oC -10 oC -38 oC -54 oC PaPaPa Pressure Altitude (MSL) 6,000 ft 10,000 ft 18,000 ft 33,000 ft 36,000 ft * Wind direction assumes that north is at the top of the page. Latitude and longitude lines, as well as other geographical references, must be used to determine actual compass direction. Table 5-11. Satellite Wind Estimate Plotting Model Examples Plotting Model 850MB 700MB 500MB 300MB 200MB Wind* 290o/30 kt 360o/20 kt 240o/10 kt 140o/165 kt 310o/60 kt PaPaPa Pressure Altitude (MSL) 7,000 ft 11,000 ft 17,000 ft 33,000 ft 36,000 ft * Wind direction assumes that north is at the top of the page. Latitude and longitude lines, as well as other geographical references, must be used to determine actual compass direction. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-31 ### Page 142 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-31. 850MB Analysis Chart Example Figure 5-32. 700MB Analysis Chart Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-32 ### Page 143 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-33. 500MB Analysis Chart Example Figure 5-34. 300MB Analysis Chart Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-33 ### Page 144 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-35. 200MB Analysis Chart Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-34 ### Page 145 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.3 Freezing-level Graphics The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0ºC. This altitude is also known as the height of the 0ºC constanttemperature surface. A freezing level chart shows the height of the 0ºC constant-temperature surface. The concept of freezing level becomes slightly more complicated when more than one altitude is determined to be at a temperature of 0ºC. These “multiple freezing layers” occur when a temperature inversion at altitudes above the defined freezing level are present. For example, if the first freezing level is at 3000 ft MSL and the second is at 7000 ft MSL, a temperature inversion is between these two altitudes. This would indicate temperatures rising above freezing above 3000 ft MSL and then back below freezing at 7000 ft MSL. The Aviation Weather Center (AWC) provides freezing level graphics available on the Aviation Digital Data Service (ADDS) web site at: http://adds.aviationweather.noaa.gov/icing/frzg_nav.php The ADDS Freezing Level graphics provide an initial analysis and forecasts at 3-, 6-, 9-, and 12- hours into the future. The forecasts are based on output from the National Weather Service’s (NWS) Rapid Update Cycle (RUC) numerical forecast model. 5.3.1 Issuance The initial analysis and 3-hour forecast graphics are updated hourly. The 6-, 9-, and 12-hour forecast graphics are updated every three hours. 5.3.2 Observational Data The RUC forecast model incorporates all of the latest weather observations in order to produce the best available analysis and forecast. These observations include: • Commercial aircraft • Profiler related: o Wind profilers (404 and boundary layer 915 MHz) o VAD (Velocity Azimuth Display) winds from WSR-88D radars o RASS (Radio Acoustic Sounding System) • Rawinsondes and special dropwinsondes • Surface: o GPS total precipitable water estimates o GOES cloud-top data (pressure and temperature) o GOES total precipitable water estimates AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-35 ### Page 146 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) o SSM/I total precipitable water estimates o GOES high-density visible and infrared (IR) cloud drift winds • Experimental: o Radar reflectivity (3-d) o Lightning o Regional aircraft data with moisture (TAMDAR) 5.3.3 Format The colors represent the height in hundreds of feet above mean sea level (MSL) of the lowest freezing level. • Regions with white indicate the surface and the entire depth of the atmosphere are below freezing. • Hatched regions represent areas where the surface temperature is below freezing with multiple freezing levels aloft. • Areas where the surface temperature is above freezing with multiple freezing levels aloft are in regions where adjacent pixels change by more than one color when compared against the color scale (e.g., orange to dark blue). The following cases illustrate the interpretation of the graphic. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-36 ### Page 147 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-36. RUC 00-hour Freezing Level Graphic Example Case 1 (Figure 5-36, Case 1) represents the condition where temperature is below freezing at the surface and all levels above the surface (represented in the graphic above by white-colored pixels). Case 2 (Figure 5-36, Case 2) represents the condition where the temperature goes above and below freezing two or more times vertically through the atmosphere while the surface temperature is less than 0°C. These regions are hatched with white. The underlying color represents the lowest height where the temperature crosses the 0°C line as shown by the blue arrow on the vertical temperature graphic. Case 3 (Figure 5-36, Case 3) represents the condition where the temperature goes above and below freezing three or more times vertically through the atmosphere while the surface AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-37 ### Page 148 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) temperature is higher than 0°C. These regions are located in areas where adjacent pixels change by more than one color when compared against the color scale. Case 4 (Figure 5-36, Case 4) is relatively simple and represents the condition where the temperature at the surface is above freezing and the air generally cools with height crossing the 0°C line once. 5.3.4 Use Freezing level graphics are used to assess the lowest freezing level heights and their values relative to flight paths. Clear, rime and mixed icing are found in layers with below-freezing (negative) temperatures and super-cooled water droplets. Users should be aware that official forecast freezing level information is specified within the AIRMET Zulu Bulletins (Contiguous U.S. and Hawaii) and the AIRMET “ICE AND FZLVL” information embedded within the Area Forecasts (Alaska only) Figure 5-37. ADDS Freezing Level Graphic Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-38 ### Page 149 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.4 Lifted Index Analysis Chart The Lifted Index Analysis Chart (Figure 5-38) provides a data plot of observed lifted index (LI) and K index values for radiosonde sites and an analysis of LI for the contiguous U.S., southern Canada and northern Mexico. Figure 5-38. Lifted Index Analysis Chart Example 5.4.1 Issuance The Lifted Index Analysis Chart is issued twice daily by the NWS and based solely on radiosonde observations from 00Z and 12Z. It is available at the NWS Fax Chart web site at: http://weather.noaa.gov/pub/fax/QXUA00.TIF. 5.4.2 Lifted Index (LI) The lifted index (LI) is a common measure of atmospheric stability. The Lifted Index Analysis Chart depicts a number associated with the stability of a surface parcel of air lifted to 500 mb. For more complete information on the computation, refer to the Aviation Weather manual (AC 00-6A). Lifted index values range from positive to negative. A positive lifted index indicates stable air. Larger positive numbers imply greater stability. A negative lifted index indicates unstable air. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-39 ### Page 150 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Larger negative numbers imply greater instability. A zero lifted index indicates neutrally stable air. 5.4.2.1 Data Plot Values of lifted index are plotted above the station circle for each available radiosonde station. Missing values are denoted with M. Station circles are blackened for LI values of zero or less. 5.4.2.2 Analysis Isopleths, or lines of equal value, of lifted index are drawn for intervals of 4 units for index values of +4 and lower. 5.4.2.3 Use of Lifted Index LI values on the Lifted Index Analysis Chart must be used with caution. The chart is only issued twice per day and significant changes can occur between chart times. LI values are typically lowest (least stable) during the afternoon due to daytime heating and highest (most stable) at sunrise due to nighttime cooling. LI values can change rapidly due to moving fronts, drylines, outflow boundaries, and other boundaries which change surface airmass characteristics. LI (and thus stability) is particularly sensitive to changes of surface dew point. Temperature changes at 500 mb also affect LI, but these changes are usually much less dramatic than those which occur with temperature and dew point near the surface. The Lifted Index Analysis chart only uses radiosonde data in its LI analysis. This means only large synoptic-scale stability patterns can be determined. Smaller, mesoscale LI variations will be missed. An unstable air mass (denoted by negative LI values) only implies the potential for thunderstorms. A lifting mechanism such as a front, dryline, upslope flow, outflow boundary from prior storms, or frictional convergence around lows and troughs is still necessary to initiate a thunderstorm. 5.4.3 K Index The K index (Figure 5-38) is a measure of thunderstorm potential based on vertical temperature lapse rate, moisture content of the lower atmosphere, and vertical extent of the moist layer. For more complete information on the computation, refer to the Aviation Weather (AC 00-6A). 5.4.3.1 Data Plot Values of K will be plotted below the station circle for each available radiosonde station. Missing values are denoted with M. No analysis of the K-index is made on the Lifted Index Chart. 5.4.3.2 Use of K Index With the K index, the higher the positive number, the likelihood of thunderstorm development is greater. The computation of the K-Index biases it in favor of general thunderstorms and it works better for non-severe convection. The K-index is also an index for forecasting heavy rain. Although K-index values can be correlated to a probability of thunderstorm occurrence, these values will vary with seasons, locations, and synoptic settings. The values listed in Table 5-12 were empirically-derived and should be used with caution. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-40 ### Page 151 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 5-12. K Index and Coverage of General Thunderstorms K INDEX West of the Rockies K INDEX East of the Rockies Coverage of General Thunderstorms less than 15 less than 20 None 15 to 20 20 to 25 Isolated thunderstorms 21 to 25 26 to 30 Widely scattered thunderstorms 26 to 30 31 to 35 Scattered thunderstorms Above 30 Above 35 Numerous thunderstorms Note: K value may not be representative of air mass if 850 mb level is near the surface. The chart only uses radiosonde data in its K index analysis. This means only large synopticscale stability patterns can be determined. Smaller, mesoscale K index variations will be missed. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-41 ### Page 152 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.5 Weather Depiction Chart The Weather Depiction Chart (Figure 5-39) contains a plot of weather conditions at selected METAR stations and an analysis of weather flying category. It is designed primarily as a briefing tool to alert aviation interests to the location of critical or near-critical operational minimums at terminals in the conterminous US and surrounding land areas. The chart can be found at: http://weather.noaa.gov/pub/fax/QGUA00.TIF Figure 5-39. Weather Depiction Chart Example 5.5.1 Issuance The Weather Depiction chart is issued eight times daily at the following times: Table 5-13. Weather Depiction Charts Issuance Schedule Valid Time (UTC) 01 04 07 10 13 16 19 22 5.5.2 Station Plot Model METAR elements (Section 2.1) associated with weather flying category (visibility, present weather, sky cover, and ceiling) are plotted for each station on the chart (Figure 5-41). The station is located at the center of the sky cover symbol. Most stations are not plotted due to space limitations. However, all reporting stations are used in the weather flying category analysis. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-42 ### Page 153 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-40. Weather Depiction Chart Station Plot Model 5.5.2.1 Visibility When visibility is 5 miles or less, it is entered to the left of the station. Visibility is entered in statute miles and fractions of a mile. 5.5.2.2 Present Weather Present weather symbols are entered to the left of the station. If the present weather information is obtained by an automated system, the right bracket symbol ( ] ) is plotted to the right of the station. When several types of weather and/or obstructions to visibility are reported, the most significant weather element is plotted. This is the first weather element coded in the METAR report (Section 2.1) and is usually the highest coded number in the Present Weather Symbols guide (Appendix I). 5.5.2.3 Sky Cover Sky cover represents the summation total of the sky condition element from the METAR report. For example, if the METAR sky condition element was SCT030 BKN060 OVC090, the sky cover would be overcast. Sky cover symbols are listed in Figure 5-41. 5.5.2.4 Ceiling Ceiling is the height from the base of the lowest layer aloft covering more than one-half the sky to the ground. Additionally, vertical visibility into a total surface-based obscuration is defined as a ceiling. For a METAR report, the first broken (BKN) or overcast (OVC) layer is the ceiling. For example, if the METAR sky condition element is SCT030 BKN060 OVC090, the ceiling is 6,000 feet. For stations with broken to overcast layers, the ceiling height is plotted below the station. Ceilings are reported as hundreds of feet above ground level (AGL). AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-43 ### Page 154 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) For a total surface-based obscuration, no ceiling is plotted and the METAR must be consulted. Partial obscurations are not identified. • For a partial obscuration with no layer above, the sky cover symbol will be plotted as missing (Figure 5-41). • For a partial obscuration with a layer above, the sky cover and ceiling height will be plotted for the cloud layer only. The METAR report should be consulted to identify the partial obscuration. If the sky cover is clear, few, or scattered, no ceiling is plotted. 5.5.3 Weather Flying Category Analysis Instrument Flight Rules (IFR) indicated on the Weather Depiction Chart represents ceilings less than 1,000 feet and/or visibility less than 3 statute miles and IFR operations must be in place. IFR areas are outlined on the chart with a solid line and are shaded. IFR areas are typically shaded red in colorized versions of the chart. Marginal Visual Flight Rules (MVFR) indicated on the Weather Depiction Chart represents ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 statute miles and VFR operations can take place. MVFR areas are outlined with a solid line, but the area is not shaded. MVFR areas are typically shaded blue in colorized versions of the chart. Visual Flight Rules (VFR) indicated on the Weather Depiction Chart represents a ceiling greater than 3,000 feet or clear skies and visibility greater than 5 statute miles and VFR operations can take place. VFR conditions are not analyzed. This does not necessarily imply that the sky is clear. 5.5.4 Use The Weather Depiction Chart is an ideal place to begin flight planning or to prepare for a weather briefing. This chart provides an overview of weather flying categories and other adverse weather conditions for the chart valid time. The chart, though, may not completely represent the en route conditions because of terrain variations and the possibility of weather occurring between reporting stations. This chart should be used in addition to the current METAR reports, pilot weather reports, and radar and satellite imagery for a complete look at the latest flying conditions. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-44 ### Page 155 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.6 Alaska Weather Depiction Charts The Alaska Weather Depiction Charts (Figure 5-43) display color coded station plots which show: temperature, dew point, ceiling, visibility and wind direction/speed. A key to the station plots is found on each map. So pal Pan SCYPC ￾45 PASC39 48 15Ф CYUB 999 „CYU SS "CYEV PARD 15 240m _PAKP 59' CYOC 54 CZFM PAOT, 54 PAFM Y 1999 35¢ • 210 ı20 DE 38) 110 / 58 'CZFN 19" 80; 10@PFYU 2 6799СКА2 PAUN S4 Ø150i PAEM 16 9999 1530 999 991999 ¡ PATK 799 PAS· 5115419KILA2 999 /PACV. SO PREM -42 158, PAKN GAILSO 999™ 19 999 _ PAHO- 3_90 18. 70 49 54 PAJN 5E 460 IÇWDL 10( 999 SO PAST 15 _ PAWG РАРН MP(des SoW DEWPT (deg F) | CIG 172 07/14/2005 IFR MYFRAYFR 190 Figure 5-41. AAWU Alaska Weather Depiction Chart Example Thirteen charts cover Alaska (except for the Aleutians) and adjacent areas of Canada. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-45 ### Page 156 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Table 5-14. AAWU Alaska Weather Depiction Charts Coverage Chart Coverage Scale Entire State of Alaska (1:12 million) All of Southeast Alaska (1:5 million) Southern Southeast Alaska (1:3 million) Northern Southeast Alaska (1:3 million) North Gulf Coast (1:5 million) South Central Alaska (1:5 million) Cook Inlet/Susitna Valley (1:2 million) Southwest Alaska (1:6 million) Western Interior (1:5 million) Central Interior (1:5 million) Northern Alaska (1:6 million) Southwest British Columbia (1:7 million) Yukon Territory/Northern British Columbia (1:8 million) 5.6.1 Issuance The charts are issued hourly and can be found on the Alaska Aviation Weather Unit (AAWU) web site at: http://aawu.arh.noaa.gov/Sigwx.php. The charts will first appear at about 10 minutes past the hour, with a second update at about 25 minutes past the hour. 5.6.2 Legends The Alaska Weather Depiction Charts depict numerous parameters including the flying category, sky cover and wind. 5.6.2.1 Flying Category Each station plot is color-coded according to the weather flying category reported (Table 5-16). Red indicates instrument flight rules (IFR), blue indicates marginal visual flight rules (MVFR), and black is plotted for stations reporting visual flight rules (VFR). Table 5-15 AAWU Alaska Weather Flying Categories and Criteria FLYING CATEGORY CEILING (feet) VISIBILITY (miles) VFR (black) Greater than 3,000 feet Greater than 5 miles MVFR (blue) 1,000 to 3,000 feet 3 to 5 miles IFR (red) Less than 1,000 feet Less than 3 miles 5.6.2.2 Station Plot METAR elements are plotted for each station on the chart (Figure 5-45). Some stations are not plotted due to space limitations, notably on the chart which covers the entire state of Alaska. Figure 5-42. AAWU Alaska Weather Depiction Chart Station Plot Legend AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-46 ### Page 157 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.6.2.3 Sky Cover The sky cover symbol is plotted at the station location and is filled according to the summation total of the sky condition element from the METAR report. For example, if the METAR sky condition element was SCT030 BKN060 OVC090, the sky cover would be overcast. Sky cover symbols are listed in Figure 5-41. 5.6.2.4 Station Identifier (STNID) The four-letter ICAO station identifier is entered to the upper right of the station. 5.6.2.5 Wind Wind is plotted in increments of 5 knots (kts). The wind direction is referenced to “true” north and is depicted by a stem (line) pointed in the direction from which the wind is blowing. Wind speed is determined by adding the values of the flags (50 kts), barbs (10kts), and half barbs (5 kts) found on the stem. A single circle over the station with no wind symbol indicates a calm wind. Some sample wind symbols are shown on Figure 5-46. Figure 5-43. AAWU Alaska Weather Depiction Chart Wind Symbols 5.6.2.6 Temperature (TMP deg F) Temperature in degrees Fahrenheit is plotted to the upper left of the sky cover symbol. 5.6.2.7 Visibility (VIS) Visibility in statute miles is plotted to the left of the sky cover symbol. Decimals are used to represent tenths of miles when necessary. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-47 ### Page 158 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.6.2.8 Dew Point Temperature (DEWPT deg F) Dew point temperature in degrees Fahrenheit is plotted to the lower left of the sky cover symbol. 5.6.2.9 Ceiling (CIG) Ceiling is the height from the base of the lowest layer aloft covering more than one-half the sky. Additionally, vertical visibility into a total surface-based obscuration is defined as a ceiling. For a METAR report, the first broken (BKN) or overcast (OVC) layer is the ceiling. For example, if the METAR sky condition element is SCT030 BKN060 OVC090, the ceiling is 6,000 feet. For a total surface-based obscuration, no ceiling is plotted and the METAR must be consulted. If the sky cover is clear, few, or scattered, no ceiling is plotted. The ceiling is plotted to the lower right of the station circle. Ceilings are reported as hundreds of feet above ground level (AGL). If no ceiling is present, the code 999 will be plotted. 5.6.2.10 Present Weather (WX) Present weather symbols are entered to the left of the station. Note that the older Surface Aviation Observation (SAO) code is used instead Surface Analysis Chart symbols or the modern METAR code. Table 5-16 Alaska Weather Depiction Charts Precipitation Symbols Table 5-17 Alaska Weather Depiction Charts Obstruction to Visibility Symbols Symbol Meaning Symbol Meaning T Thunderstorm BD Blowing Dust R Rain BN Blowing Sand RW Rain Shower BS Blowing Snow L Drizzle BY Blowing Spray ZR Freezing Rain D Dust ZL Freezing Drizzle F Fog A Hail GF Ground Fog IP Ice Pellets H Haze IPW Ice Pellet Showers IF Ice Fog S Snow K Smoke SW Snow Showers SP Snow Pellets SG Snow Grains IC Ice Crystals Table 5-18 Alaska Weather Depiction Charts Precipitation Intensity Symbols Symbol Meaning - Light (No symbol) Moderate + Heavy AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-48 ### Page 159 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.6.3 Use The Alaska Weather Depiction Charts provide an overview of weather flying categories and other adverse weather conditions for the chart valid time. The chart often does not completely represent the en route conditions because of terrain variations and the possibility of weather occurring between reporting stations. These charts should be used in addition to the latest METAR/SPECIs, pilot weather reports, and radar and satellite imagery for a complete look at the latest flying conditions. 33 43 PLERZ 45 PAFK 3QФ 999 A PACK 45 _PASW 36 PAZk 43 40 48 PAAG PAER 19 PS BABY 999 PASY 27 SMCAZ PALV |44 SORT _PAWR PAEN 10• 60 RUFAZ 38 45. PAL. *KNTUS 36®50 NABAZ 19945 42 PAIL ILI SURFACE OBSERVATIONS PAHO? IMP(devISOWX ISTNID 182 05/04/2005 IFR_MVFR VFR DEWPT(deg F) _ CIG Figure 5-44. AAWU Alaska Weather Depiction Chart - South Central Alaska Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-49 ### Page 160 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.7 Radar Summary Chart The Radar Summary Chart (Figure 5-49) is a computer-generated mosaic of radar echo intensity contours based on Radar Weather Reports (Section 2.3) over the contiguous U.S. Possible precipitation types, cell movements, maximum tops, locations of line echoes, and remarks are plotted on this chart. Much of this information is often truncated due to space limitations. Severe thunderstorm and tornado watches are plotted if they are in effect when the chart is valid. The Radar Summary Chart is available on the National Weather Service (NWS) Fax Charts web site at: http://weather.noaa.gov/pub/fax/QAUA00.TIF 0920Z MON 13 JUN 2005 RADAR SUMMARY SD095- 220 NE 220 NE NE NE 28 RW NE ¿ NE NE • NE **NE NE R 190 NEVA NE NE 260 NE NA NET 137 NE NE NE NE -NE.** **NE NA NE NE NE NE NA NE NE NE LEGEND. NE ECHO AREAS INTENSITIES 1-3-5 NE NE** WEATHER WAT START END S ¡ PRECIPITATION SPEED NOAA/NUS/NCEP WASHINGTỔN IS DEPT OF COMMERCE NCEP + 09202 MON 13 JUN 2005 RADAR SUMMARY SD09 Figure 5-45. Radar Summary Chart Example 5.7.1 Issuance The chart is issued hourly. Figure 5-50 depicts the WSR-88D weather radar network from which the chart is produced. 5.7.2 Format The Radar Summary Chart depicts precipitation type, intensity, coverage, movement, echoes, and maximum tops. 5.7.2.1 Precipitation Type The precipitation type, determined by a computer model, is indicated on the chart by symbols located adjacent to the precipitation areas. These symbols (Table 5-20) are not in METAR AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-50 ### Page 161 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) format. Freezing precipitation is not reported in Radar Weather Reports and, thus, not plotted on the Radar Summary Chart. Table 5-19. Radar Summary Chart Precipitation Type Symbols SYMBOL MEANING R Rain RW Rain shower S Snow SW Snow shower T Thunderstorms 5.7.2.2 Precipitation Intensity The six precipitation intensity levels coded in the Radar Weather Report are consolidated into three contour intervals for the Radar Summary Chart (Figure 5-47). Precipitation intensity is correlated only for liquid precipitation, not solid precipitation (e.g., snow). KOT· KMSX KGGW * KMBX O KNVY KULI OKIEX ÖKBIS KELA KABR O КМРУ KCEB : КМАХ KUDK KF SDO KARY KHKX KBCI KDYN A KLOT KOLEO ALŘx KCTS курх FOAK O KIWx TO KUX KDAX KFTCO O KELD KIWXO CKLEX KIL O in St KIND OKIN OKIE KPUX O KODCO OESGF OKHPE KEYXO OEVIX кРУх KAEX. KUND KIN • CECAF OKNEX YO KIWA KYDS OKIBB IDE CRAMA CATLE KIZK ксио квих KYUX KHỐX КИАГ OKFYS OKSHV КРОЕ EJAN KFOXO O EVA KGEK O PAPD POTA C Figure 5-46. WSR-88D Weather Radar Network AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-51 ### Page 162 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 5-47. Radar Summary Chart Precipitation Intensity 5.7.2.3 Echo Coverage All of the shaded areas within the contours are assumed to contain precipitation. However, actual precipitation coverage is less. This is because only a fraction of a grid box needs to be covered with echoes for the entire grid box to be plotted as precipitation on the chart. 5.7.2.4 Line Echoes When precipitation echoes are reported as a LINE, a line will be drawn through them on the chart (see Table 5-21). Where there is 8/10ths or more coverage, the line is labeled as solid (SLD) at both ends. Table 5-20. Radar Summary Chart Echo Configuration Symbols **SYMBOL MEANING** 8/10ths or greater coverage in a line. Line of echoes. Solid line of thunderstorms with intense to extreme precipitation. 5.7.2.5 Cell Movement Cell movement is the average motion of all cells within a configuration. An arrow indicates direction of cell movement. Speed in knots is entered near the arrowhead. LM identifies little AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-52 ### Page 163 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) movement. Movement of areas and lines can be significantly different from the motion of the individual cells that comprise these configurations. Table 5-21. Radar Summary Chart Cell Movement Examples **SYMBOL MEANING** Cell movement to the northeast at 35 knots Cell movement to the east at 24 knots Cell movement to the south at 18 knots Cell movement to the southwest at 12 knots LM Little cell movement 5.7.2.6 Maximum Top Figure 5-48. Radar Summary Chart Maximum Top Example A maximum top is the altitude of the highest precipitation echo as coded on a Weather Radar Report (Section 2.3). Altitudes are sometimes augmented by satellite data. Individual Radar Weather Reports should be used to determine if satellite data was used for precipitation echo tops. Tops are plotted in 3-digit groups representing height in hundreds of feet MSL and are underlined. Where it is necessary to offset a top for reasons of insufficient space, a line is drawn from one end of the underline to a small black square which represents the location of the top. Maximum echo top does not equal maximum cloud top. The maximum echo top is the altitude of the highest light precipitation echo, not highest cloud top. Also, all radar heights are approximations due to radar wave propagation variations depending on atmosphere conditions. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-53 ### Page 164 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.7.2.7 Weather Watch Areas Heavy dashed lines outline Tornado (WT) (Section 5.5.2) and Severe Thunderstorm (WS) Watch (Section 5.4.2) areas. The type of watch and the watch number are enclosed in a rectangle and positioned as closely as possible to the northeast corner of the watch. If there is no room at the northeast corner of the watch, the watch information is offset and connected to the watch by a thin line. The watch number is also printed at the bottom of the chart (in Mexico) together with the issuance time and expiration time under a label reading “WEATHER WATCH AREAS”. In case no weather watch is in effect, “NONE” is printed at the bottom of the chart. Table 5-22. Radar Summary Chart Weather Watch Area Examples **SYMBOL MEANING** Severe Thunderstorm Watch number 210 Tornado Thunderstorm Watch number 457 5.7.2.8 Operational Contractions Radar sites which report PPINA, PPINE, and PPIOM in their Weather Radar Reports (Section 2.3.1.10) are abbreviated to NA, NE, and OM respectively and plotted over the radar sites on the chart. Table 5-23. Radar Summary Chart Operational Contractions SYMBOL MEANING NA Not available NE No echoes OM Out for maintenance 5.7.3 Use The Radar Summary Chart aids in preflight planning by identifying areas of precipitation and highlighting its characteristics. This chart displays precipitation only; it does not display clouds, fog, fronts, or other boundaries. Therefore, the absence of echoes does not equal clear AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-54 ### Page 165 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) weather. Cloud tops will be somewhat higher than precipitation tops detected by radar. The chart must be used in conjunction with other charts, reports, and forecasts. The radar summary chart is for preflight planning only and should always be cross-checked and updated by current WSR-88D images. Once airborne, the pilot must evade individual storms by in-flight observations. This can be done by using visual sighting or airborne radar as well as by requesting weather radar information from En route Flight Advisory Service "Flight Watch" briefers at Automated Flight Service Station (AFSS). AFSS Flight Watch briefers have access to current weather radar imagery. • 1119Z TUE 28 SEP 2004 RADAR SUMMARY SD115 NE NE NE NE NE NE NE NE NE NE NE NE €NE NE NE NE NE RU -180 NA O230 NE NE NE 200 P NE NE NE NEVE SLEI NE NE **NENE NE 'NE NE NE NE NE NE NE NE WE NE** WE NA NE NA NA NA NE 340 280 WEATHER WATCH AREAS ' AREA END AREA OF PRECIPITATION SPEED NONE NOAA/NUS/NCEP WASHINGTON ПСЕР 1119Z TOE 28 SEP 2004 RADAR SUMMARY SD11 Figure 5-49. Radar Summary Chart Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-55 ### Page 166 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.8 Alaska Initial Geopotential Heights and Winds Charts The Alaska Initial Geopotential Heights and Winds Charts (Figure 5-54) display an analysis of the observed height contours and winds at selected constant pressure surfaces (flight levels). Figure 5-50. Alaskan Initial Geopotential Heights and Winds Chart Example Table 5-24. Pressure Altitudes of Alaska Initial Geopotential Heights and Winds Charts CHART PRESSURE ALTITUDE (Feet, MSL) PRESSURE ALTITUDE (Meters, MSL) 200 MB 39,000 ft 12,000 m 300 MB 30,000 ft 9,000 m 500 MB 18,000 ft 5,500 m 700 MB 10,000 ft 3,000 m 850 MB 5,000 ft 1,500 m 5.8.1 Issuance The charts are issued twice daily with valid times of 00z and 12z and can be found on the Alaska Aviation Weather Unit (AAWU) web site at: http://aawu.arh.noaa.gov/upperwinds.php. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-56 ### Page 167 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 5.8.2 Analysis The analysis of both height contours and winds are based on output from the North American Mesoscale (NAM) computer forecast model. 5.8.2.1 Height Contours Height contours are lines of constant height referenced to MSL and are used to map the height variations of constant pressure surfaces. They identify and characterize pressure systems on constant pressure charts. Contours are drawn as solid lines and labeled in meters. The intervals at which the contours are drawn are 60 meters on all of the charts. 5.8.2.2 Winds Wind is plotted in increments of 5 knots (kts). The wind direction is referenced to “true” north and is depicted by a stem (line) pointed in the direction from which the wind is blowing. Wind speed is determined by adding the values of the flags (50 kts), barbs (10kts), and half barbs (5 kts) found on the stem. A single circle over the station with no wind symbol indicates a calm wind. Figure 5-55 contains some examples wind symbols. Figure 5-51. Alaskan Initial Geopotential Heights and Winds Chart Wind Plotting Model 5.8.3 Use The Alaska Initial Geopotential Heights and Winds Charts are used to provide an overview of heights, pressure patterns and winds at specified pressure altitudes. Pressure patterns cause AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-57 ### Page 168 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) and characterize much of the weather. Typically, lows and troughs are associated with bad weather, clouds and precipitation, while highs and ridges are associated with good weather. AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-58 ### Page 169 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Weather Unit Г1580 AL AL A 200 WINDS A CONTOURS VAL 11160/2005 1ЭV 11760S - 140 Figure 5-52. Alaskan Initial Geopotential Heights and Winds Chart - 200MB Winds and Contours Chart Example A f 412 8g817 Alaska Aviation 1182 - 8940 - I Am 29O90M -90§ - 175 8820- SOONE MINDS AND CONTOURS VALID 122 5/4/2005 - 140 / -135 9120-150 Figure 5-53. Alaskan Initial Geopotential Heights and Winds Chart - 300MB Winds and Contours Chart Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-59 ### Page 170 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) W0 114 - 522967 5280 Weather Unit - 1ź5 500HB WINDS AND CONTOURS VALID 122 5/4/2005 5580- 140 Figure 5-54. Alaskan Initial Geopotential Heights and Winds Chart - 500MB Winds and Contours Chart Example - 2820. eather Unit T 3000 ·[_→ -1Ý52760. 700MB WINDS AND CONTOURS VALID 12Z 5/4/2005 ￾140 -135 - 130 Figure 5-55. Alaskan Initial Geopotential Heights and Winds Chart - 700MB Winds and Contours Chart Example AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-60 ### Page 171 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-61 Figure 5-56. Alaskan Initial Geopotential Heights and Winds Chart - 850MB Winds and Contours Chart Example ### Page 172 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6 PRODUCTS FOR AVIATION HAZARDS 6.1 Significant Meteorological Information (SIGMET) A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena which may affect the safety of aircraft operations. SIGMETs are intended for dissemination to all pilots in flight to enhance safety. SIGMETs are issued by the responsible MWO as soon as practical to give notice to operators and aircrews of potentially hazardous en-route conditions. • SIGMETs are available on the Aviation Digital Data Service (ADDS) web site at: http://adds.aviationweather.noaa.gov/airmet/ o Alaska SIGMETs are also available on the Alaska Aviation Weather Unit (AAWU) web site at: http://aawu.arh.noaa.gov/ o Hawaii SIGMETs are also available on the NWS WFO Honolulu web site at: http://www.prh.noaa.gov/hnl/pages/aviation.php 6.1.1 SIGMET Issuance SIGMETs are issued from Meteorological Watch Offices (MWO). The U.S. has three MWOs: the Aviation Weather Center (AWC), the Alaska Aviation Weather Unit (AAWU), and the Weather Forecast Office (WFO) in Honolulu. Their areas of responsibility are as follows: • The AWC: o Twenty (20) domestic Air Route Traffic Control Center (ARTCC) Flight Information Regions (FIRs) covering the conterminous U.S. (CONUS) and adjacent coastal waters (Figure 6-1). o The New York, Houston, Miami, and San Juan Oceanic FIRs (Figure 6-2). o The Oakland Oceanic FIR north of 30 north latitude, and the portion east of 140 west longitude which is between the equator and 30 north latitude (Figure 6-3). • The AAWU is responsible for the Anchorage Continental FIR and Anchorage Oceanic FIR (Figure 6-3). • WFO Honolulu is responsible for the Oakland Oceanic FIR south of 30 north latitude and between 140 west and 130 east longitude (Figure 6-3). AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-1 ### Page 173 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) San Francisco Chicago Boston Salt Lake City Dallas/Fort Worth Miami Figure 6-1. AWC SIGMET Areas of Responsibility - Conterminous U.S. **NEW YORK OCEANIC FIR** • 130 **HOUSTON MIAMI** OCEANIC OCEANIC Q MIAMI FIR FIR OCEANIÇ SER SAN JUAN ı20 → FIR - 90 - 80 <øБ0 -50 -40 Figure 6-2. AWC SIGMET Areas of Responsibility - Atlantic Basin AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-2 ### Page 174 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-3. SIGMET Areas of Responsibility – Pacific Basin 6.1.1.1 SIGMET Identification When a SIGMET is issued, it is assigned a unique series identifier: • AWC for CONUS o NOVEMBER through YANKEE, excluding SIERRA and TANGO • AWC for Oakland Oceanic FIR o ALFA through HOTEL • Honolulu MWO for Oakland Oceanic FIR o NOVEMBER through ZULU • AAWU for Anchorage FIR o INDIA through MIKE AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-3 ### Page 175 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) A number is assigned sequentially with each issuance until the phenomenon ends. At 0000 UTC each day, all continuing SIGMETs are renumbered to one (1) regardless of a continuation of the phenomena. (e.g., YANKEE 1, YANKEE 2, YANKEE 3, etc.) 6.1.2 SIGMET Standardization SIGMETs follow these standards: • All heights or altitudes are referenced to above mean sea level (AMSL), unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 feet, the level is preceded by FL to represent flight levels (e.g., FL180). • References to latitude and longitude are in whole degrees and minutes following the model: Nnn[nn] or Snn[nn], Wnnn[nn] or Ennn[nn] with a space between latitude and longitude and a hyphen between successive points. Example: N3106 W07118 – N3011 W7209 • Messages are prepared in abbreviated plain language using contractions from the Federal Aviation Administration (FAA) Order 7340.1Z for domestic products and International Civil Aviation Organization (ICAO) document 8400 for international products issued for Oceanic FIRs. A limited number of non-abbreviated words, geographical names and numerical values of a self-explanatory nature may also be used. • Weather and obstructions to visibility are described using the weather abbreviations for surface weather observations (METAR/SPECI). See the Federal Meteorological Handbook (FMH) No. 1 – Surface Observations or Section 3.1 of this document. Note: Refer to Appendix A for definitions of common terms used in SIGMETs. 6.1.3 SIGMET (Non-Convective) – Conterminous U.S. 6.1.3.1 SIGMET (Non-Convective) Issuance Criteria – Contiguous U.S. A SIGMET may be issued in the Contiguous U.S. when any of the following conditions are affecting or, in the judgment of the forecaster, are expected to affect an area of at least 3,000 square miles or an area judged to have a significant impact on the safety of aircraft operations. • Severe or greater Turbulence (SEV TURB) • Severe Icing (SEV ICE) • Widespread Duststorm (WDSPR DS) • Widespread Sandstorm (WDSPR SS) • Volcanic Ash (VA) AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-4 ### Page 176 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.1.3.2 SIGMET (Non-Convective) Issuance Time and Valid Period – Conterminous U.S. A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a 4-hour period. A SIGMET can have a valid period up to, but not exceeding, four (4) hours. SIGMETs for continuing phenomena will be reissued at least every 4 hours as long as SIGMET conditions continue to occur in the area for responsibility. 6.1.3.3 SIGMET (Non-Convective) Format – Conterminous U.S. The content and order of elements in the SIGMET are as follows: • series name and number • valid beginning and ending time (UTC) • list of states affected by the phenomena • location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time • phenomena description (e.g., SEV ICE) • vertical extent (base and top), if appropriate • movement, if appropriate • intensity change (INTSF – intensifying, WKN – weakening, NC – no change) • Indication that the whether the condition will continue during the 4 hours beyond the valid time of the SIGMET AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-5 ### Page 177 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-4. SIGMET for the Conterminous U.S. Decoding Example Table 6-1. Decoding a SIGMET (Non-Convective) for the Conterminous U.S. Line Content Description 1 SFO SIGMET area identifier R SIGMET series WS Product identifier 100130 Issuance date/time UTC 2 SIGMET Product type ROMEO SIGMET series name 1 Series issuance number VALID UNTIL 100530 Ending valid date/time UTC 3 OR WA Phenomenon location (states) 4 FROM SEA TO PDT TO EUG TO SEA Phenomenon location (highaltitude VOR coordinates) 5 OCNL MOGR CAT BTN FL280 AND FL350 EXP DUE TO JTSTR. CONDS BGNG AFT 0200Z CONTG BYD 0530Z AND SPRDG OVR CNTRL ID BY 0400Z. Phenomenon description The SIGMET in Figure 6-4 is decoded as the following: (Line 1) SIGMET ROMEO series issued for the San Francisco Area at 0130 UTC on the 10th day of the month. (Line 2) This is the first issuance of the SIGMET ROMEO series and is valid until the 10th day of the month at 0530 UTC. (Line 3) The affected states within the SFO area are Oregon and Washington. (Line 4) From Seattle, WA; to Pendleton, OR; to Eugene, OR; to Seattle, WA; AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-6 ### Page 178 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (Line 5) Occasional moderate or greater clear air turbulence between Flight Level 280 and Flight Level 350, expected due to jet stream. Conditions beginning after 0200Z continuing beyond 0530Z and spreading over central Idaho by 0400Z. 6.1.3.4 SIGMET (Non-Convective) Cancellations – Conterminous U.S. A CONUS non-convective SIGMET is canceled when the phenomena is no longer occurring or no longer expected to occur or has moved out of the area of responsibility. 6.1.3.5 SIGMET (Non-Convective) Amendments – Conterminous U.S. Amendments to CONUS non-convective SIGMETs are NOT issued. Instead, a new SIGMET is issued using the next series number. 6.1.3.6 SIGMET (Non-Convective) Corrections – Conterminous U.S. Corrections to CONUS non-convective SIGMETs are issued as necessary. The corrected SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time. 6.1.3.7 SIGMET (Non-Convective) Example – Conterminous U.S. **WSUS01 KKCI 050600 WS1R BOSR WS 050600 SIGMET ROMEO 2 VALID UNTIL 051000** ME NH VT FROM CAR TO YSJ TO CON TO MPV TO CAR SEV TURB OBS AND FCST BLW 080. CONDS CONTG BYD 1000Z. SIGMET (WSUS01) issued by the Meteorological Watch Office (WMO) (Aviation Weather Center) in Kansas City, Missouri (KKCI) on the 5th day of the month at 0600 UTC. The National Weather Service AWIPS communication header for this product is WSR1. SIGMET issued for the Boston Area Forecast region on the 5th day of the month at 0600 UTC. This is the second (2nd) issuance of SIGMET series Romeo and is valid until the 5th day of the month at 1000 UTC. The affected states are Maine (ME), New Hampshire (NH) and Vermont (VT). Within an area bounded from Caribou, Maine (CAR) to St. Johns, New Brunswick (YSJ); to Concord, New Hampshire (CON); to Montpelier, Vermont (MPV); to Caribou, Maine (CAR). Severe turbulence observed and forecast below 8,000 feet. Conditions continuing beyond 1000 UTC. 6.1.4 Convective SIGMET Convective SIGMETs are issued for the conterminous U.S. (CONUS) instead of SIGMETs for thunderstorms. Any Convective SIGMET implies severe or greater turbulence, severe icing, and low level wind shear. 6.1.4.1 Convective SIGMET - Routine Issuance Criteria A Convective SIGMET will be issued when any of the following conditions are occurring or, in the judgment of the forecaster, are expected to occur: • A line of thunderstorms at least 60 miles long with thunderstorms affecting at least 40 percent of its length. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-7 ### Page 179 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • An area of active thunderstorms affecting at least 3,000 square miles covering at least 40 percent of the area concerned and exhibiting a very strong radar reflectivity intensity or a significant satellite or lightning signature. • Embedded or severe thunderstorm(s) expected to occur for more than 30 minutes during the valid period regardless of the size of the area. 6.1.4.2 Convective SIGMET - Special Issuance Criteria A special Convective SIGMET may be issued when any of the following criteria are occurring or, in the judgment of the forecaster, are expected to occur for more than 30 minutes of the valid period. • Tornado, hail greater than or equal to ¾ inch (at the surface), or wind gusts greater than or equal to 50 knots (at the surface) are reported. • Indications of rapidly changing conditions, if in the forecaster’s judgment, they are not sufficiently described in existing Convective SIGMETs. • Special issuance is not required for a valid Convective SIGMET. 6.1.4.3 Convective SIGMET Issuance Time and Valid Period Convective SIGMET bulletins for the eastern, central and western regions of the conterminous U.S. (Figure 6-5) are issued on a scheduled basis, hourly at 55 minutes past the hour. Each bulletin contains all valid Convective SIGMETs within the region. Convective SIGMETs are valid for two (2) hours or until superseded by the next hourly issuance. A Convective SIGMET bulletin must be transmitted each hour for each region. When conditions do not meet or are not expected to meet Convective SIGMET criteria within a region at the scheduled time of issuance a “CONVECTIVE SIGMET...NONE” message is transmitted. Figure 6-5. AWC Convective SIGMET Areas of Responsibility AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-8 ### Page 180 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.1.4.4 Convective SIGMET Format Each Convective SIGMET bulletin includes one or more individually numbered Convective SIGMETs for the region. The content and order of each bulletin is as follows: • CONVECTIVE SIGMET series number and region letter (E, W or C) • Valid ending time (UTC) • list of states affected by the phenomena • location of phenomena delineated by high-altitude VOR coordinates covering the affected area during the SIGMET valid time • phenomena description (e.g., AREA SEV EMBD TS) • movement (e.g., MOV FROM 26030KT) • cloud top (e.g., TOPS ABV FL450) • remarks (e.g., TORNADOES...HAIL TO 2.5 IN...WIND GUSTS TO 70KT POSS) Note: Tropical Cyclone information will be added to remarks section of the CONUS Convective SIGMETs when appropriate. Note: Refer to Appendix A for definitions of common terms used in Convective SIGMETs. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-9 ### Page 181 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-6. Convective SIGMET Decoding Example Table 6-2. Decoding a Convective SIGMET Line Content Description 1 MKC Issuing Office (AWC) C Region (East, Central or West) WST Product Identifier 221855 Issuance date/time (DDHHMM) 2 CONVECTIVE SIGMET Product type 20 Issuance number C Region (East, Central or West) 3 VALID UNTIL 2055Z Valid ending time (UTC) 4 ND SD States/areas affected 5 FROM 90W MOT-GFK-ABR-90W MOT Phenomenon location (high altitude VOR coordinates) 6 INTSFYG AREA SEV TS MOVG FROM 24045KT. TOPS ABV FL450. WIND GUSTS TO 60KTS RPRTD. TORNADOES…HAIL TO 2 IN… WIND GUSTS TO 65KTS POSS ND PTN Phenomenon description, movement, cloud top, remarks The Convective SIGMET in Figure 6-6 is decoded as the following: (Line 1) Convective SIGMET issued for the central portion of the United States on the 22nd at 1855Z. (Line 2) This is the 20th Convective SIGMET issued on the 22nd for the central United States as indicated by “20C.” (Line 3) Valid until 2055Z AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-10 ### Page 182 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (Line 4) The affected states are North and South Dakota. (Line 5) From 90 nautical miles west of Minot, ND; to Grand Forks, ND; to Aberdeen, SD; to 90 nautical miles west of Minot, ND. (Line 6) An intensifying area of severe thunderstorms moving from 240 degrees at 45 knots (to the northeast). Thunderstorm tops above Flight Level 450. Wind gusts to 60 knots reported. Tornadoes, hail to 2 inches in diameter, and wind gusts to 65 knots possible in the North Dakota portion. 6.1.4.5 Convective SIGMET Outlook Each Convective SIGMET bulletin includes a 2- to 6-hour outlook at the end of the bulletin. The content and order of each bulletin is as follows: • Beginning and ending valid times • Location of expected Convective SIGMET issuances delineated by high-altitude VOR coordinates for the outlook valid time. • Discussion of forecast 6.1.4.6 Convective SIGMET Cancellations Convective SIGMETs are not cancelled but are superseded by the next Convective SIGMET in the series. 6.1.4.7 Convective SIGMET Amendments Amended Convective SIGMETs are NOT issued. Instead, a new Convective SIGMET is issued for that region. 6.1.4.8 Convective SIGMET Corrections Corrections to Convective SIGMETs are issued as necessary. The corrected Convective SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time. 6.1.4.9 Convective SIGMET Bulletin Examples **WSUS33 KKCI 091855 SIGW CONVECTIVE SIGMET...NONE .** **OUTLOOK VALID 092055-100055 TS ARE NOT EXPD.** Convective SIGMET bulletin for the western region of the conterminous U.S.(WSUS33) issued by the Meteorological Watch Office (WMO) (Aviation Weather Center) in Kansas City, Missouri (KKCI) on the 9th day of the month at 1855 UTC. The National Weather Service AWIPS communication header for this product is SIGW. No Convective SIGMETs are in effect. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-11 ### Page 183 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) The outlook portion of the Convective SIGMET bulletin is valid from the 9th day of the month at 2055 UTC to the 10th day of the month at 0055 UTC. Thunderstorms are not expected. WSUS32 KKCI 091855 SIGC MKCC WST 091855 CONVECTIVE SIGMET 21C VALID UNTIL 2055Z AR OK FROM 20S RZC-40SSW FSM DMSHG LINE TS 25 NM WIDE MOV FROM 27025KT. TOPS TO FL320. . OUTLOOK VALID 092055-100055 FROM 40NE BUM-60SE SGF-50WSW LIT-40W GGG-60ENE ABI-ADM-50WNW BUM-40NE BUM WST ISSUANCES EXPD. REFER TO MOST RECENT ACUS01 KWNS FROM STORM PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS. Convective SIGMET bulletin for the central region of the conterminous U.S.(WSUS32) issued by the Meteorological Watch Office (Aviation Weather Center) in Kansas City, Missouri (KCCI) on the 9th day of the month at 1855 UTC. The National Weather Service AWIPS communication header for this product is SIGC. Convective SIGMET (WST) for the central region of the conterminous U.S. issued by the Aviation Weather Center in Kansas City, Missouri (MKCC) on the 9th day of the month at 1855 UTC. Convective SIGMET 21C is the 21st Convective SIGMET issued for the central region of the conterminous US on the 9th day of the month. Valid until 2055 UTC. States affected are Arkansas (AR) and Oklahoma (OK). Bounded within an area from 20 nautical miles south of Razorback, Arkansas (RZC), to 40 nautical miles south-southwest of Fort Smith, Arkansas (FSM). A diminishing line of thunderstorms 25 nautical miles wide moving from 270 degrees (to the east) at 25 knots. Thunderstorms tops to FL320 (approximately 32,000 ft MSL). The outlook portion of the Convective SIGMET bulletin is valid from the 9th day of the month at 2055 UTC to the 10th day of the month at 0055 UTC. Within an area bounded from 40 nautical miles northeast of Butler, Missouri (BUM), to 60 nautical miles southeast of Springfield, MO (SGF), to 50 nautical miles west-southwest of Little Rock, Arkansas (LIT), to 40 nautical miles west of Longview, Texas (GGG), to 60 nautical miles east-northeast of Abilene, Texas (ABI), to Ardmore, Oklahoma (ADM), to 50 nautical miles west-northwest of Butler, Missouri (BUM), to 40 nautical miles northeast of (BUM). Convective SIGMET issuances are expected. Refer to the most recent Day 1 Convective Outlook (ACUS01 KWNS) from the Storm Prediction Center (SPC) for a synopsis and meteorological details. 6.1.4.9.1 Convective SIGMET Bulletin – Tropical Cyclone Example **WSUS31 KKCI 211355 SIGE MKCE WST 211355 CONVECTIVE SIGMET 1E VALID UNTIL 1555Z** NC SC FL GA AND CSTL WTRS AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-12 ### Page 184 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) FROM 30SSE CLT-160SE ILM-140ENE OMN-60E TLH-ABY-30SSE CLT AREA SEV EMBD TS MOV FROM 21015KT. TOPS ABV FL450. **TORNADOES...WIND GUSTS TO 60KT POSS.** **TS ASSOCD WITH TROPICAL STORM ALBERTO.** . OUTLOOK VALID 211555-211955 FROM 30E RDU-180SE ECG-140SSE ILM-180E PBI-40SE PBI-40S EYW-90SW EYW-70W SRQ-50N CTY-40N MCN-30NW SPA-30E RDU REF WW 475. WST ISSUANCES EXPD. REFER TO MOST RECENT ACUS01 KWNS FROM STORM PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS. REFER TO MOST RECENT WTNT21 KNHC FROM TROPICAL PREDICTION CENTER FOR DETAILS ON TROPICAL STORM ALBERTO. Convective SIGMET bulletin for the eastern region of the conterminous U.S.(WSUS31) issued by the Meteorological Watch Office (Aviation Weather Center) in Kansas City, Missouri (KCCI) on the 21st day of the month at 1355 UTC. The National Weather Service AWIPS communication header for this product is SIGE. Convective SIGMET (WST) for the eastern region of the conterminous U.S. issued by the Aviation Weather Center in Kansas City, Missouri (MKCE) on the 21st day of the month at 1355 UTC. Convective SIGMET 1E is the 1st Convective SIGMET issued for the eastern region of the conterminous US on the 21st day of the month. Valid until 1555 UTC. States affected are North Carolina (NC), South Carolina (SC), Florida (FL), Georgia (GA) and adjacent coastal waters. Within an area bounded from 30 nautical miles south-southeast of Charlotte, North Carolina (CLT) to 160 nautical miles southeast of Wilmington, North Carolina (ILM) to 140 nautical miles east-northeast of Ormond Beach, Florida (OMN) to 60 nautical miles east of Tallahassee, Florida (TLH) to Albany, Georgia (ABY) to 30 nautical miles south-southeast of Charlotte, North Carolina (CLT). An area of severe embedded thunderstorms moving from 210 degrees at 15 knots. Cumulonimbus tops above flight level 450 (approximately 45,000 feet MSL) Tornadoes and surface wind gust to 60 knots are possible. The thunderstorms are associated with Tropical Storm Alberto. The outlook portion of the Convective SIGMET bulletin is valid from the 21st day of the month at 1555 UTC to the 21st day of the month at 1955 UTC. Within an area bounded from 30 nautical miles east of Raleigh-Durham, North Carolina (RDU) to 180 nautical miles southeast of Elizabeth City, North Carolina (ECG) to 140 south-southeast of Wilmington, North Carolina (ILM) to 180 nautical miles east of (PBI) to 40 nautical miles southeast of West Palm Beach, Florida (PBI) to 40 nautical miles south of Key West, Florida (EYW) to 90 nautical miles southwest of Key West, Florida (EYW) to 70 nautical miles west of Sarasota, Florida (SRQ) to 50 nautical miles north of Cross City, Florida (CTY) to 40 nautical miles north of Macon, Georgia (MCN) to 30 nautical miles northwest of Sparta, Georgia (SPA) to 30 nautical miles east of Raleigh-Durham, North Carolina (RDU). Refer to Weather Watch Notification Message 475. Convective SIGMET issuances are expected. Refer to the most recent Day 1 Convective Outlook (ACUS01 KWNS) from the Storm Prediction Center (SPC) for a synopsis and meteorological details. Refer to the most recent Tropical Cyclone Forecast/Advisory (WTNT21 KNHC) from the Tropical Prediction Center (TPC) for details on Tropical Storm Alberto. 6.1.5 SIGMET – Outside the Conterminous U.S. (O-CONUS) AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-13 ### Page 185 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.1.5.1 SIGMET Issuance Criteria – Outside the Conterminous U.S. (O-CONUS) SIGMETs outside the Conterminous U.S. (O-CONUS SIGMETs) are issued when any of the following is occurring or expected to occur affecting an area greater than 3,000 square miles or, in the judgment of the forecaster, an area having the potential to have a significant effect on the safety of aircraft operations. • Thunderstorm - of type below * o Obscured (OBSC TS) o Embedded (EMBD TS) o Widespread (WDSPR TS) o Squall line (SQL TS) o Isolated severe (ISOL SEV TS) • Severe Turbulence (SEV TURB) • Severe Icing (SEV ICE) o With Freezing rain (SEV ICE (FZRA) • Widespread Duststorm (WDSPR DS) • Widespread Sandstorm (WDSPR SS) • Volcanic Ash (VA) • Tropical Cyclone (TC) NOTE: Obscured, embedded, or squall line thunderstorms do not have to reach 3,000 square miles criteria. *Tornado (TDO), Funnel Cloud (FC), Waterspout (WTSPT), and Heavy Hail (HVY GR) may be used as a further description of the thunderstorm as necessary. 6.1.5.2 SIGMET Issuance Time and Valid Period – Outside the Conterminous U.S. (O- CONUS) A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a 4-hour period. A SIGMET outside the conterminous U.S. (O-CONUS) can have a valid period up to, but not exceeding, four (4) hours, except for volcanic ash (VA) and tropical cyclone (TC) which can be valid up to six (6) hours. SIGMETs for continuing phenomena will be reissued at least every 4 (or 6) hours as long as SIGMET conditions continue to occur in the area for responsibility. 6.1.5.3 SIGMET Format – Outside the Conterminous U.S. (O-CONUS) O-CONUS SIGMETs contain the following information, related to the specific phenomena and in the order indicated: AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-14 ### Page 186 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • Phenomenon and its description (e.g., SEV TURB). • An indication whether the information is observed, using OBS and/or FCST. The time of observation will be given in UTC. • Location of the phenomenon referring, where possible to latitude and longitude, and flight levels (altitude) covering the affected area during the SIGMET valid time. SIGMETs for volcanic ash cloud and tropical cyclones contain the positions of the ash cloud, tropical cyclone center and radius of convection at the start of the validity time of the SIGMET. • Movement towards or expected movement using sixteen points of the compass, with speed in knots, or stationary, if appropriate. • Thunderstorm maximum height as FL. • Changes in intensity; using as appropriate, the abbreviations Intensifying (INTSF), Weakening (WKN), or No Change (NC). • Forecast position of volcanic ash cloud or the center of the tropical cyclone at the end of the validity period of the SIGMET message. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-15 ### Page 187 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-7. SIGMET Outside the Conterminous U.S. Decoding Example Table 6-3. Decoding a SIGMET Outside of the Conterminous U.S. (O-CONUS) Line Content Description 1 WSPA07 ICAO communication header PHFO Issuance MWO 010410 Issuance UTC date/time 2 SIGPAT NWS AWIPS communication header 3 KZOA Area Control Center SIGMET Product type TANGO SIGMET series 2 Issuance number VALID 010410/010800 Valid period UTC date/time PHFO Issuance office 4 OAKLAND OCEANIC FIR Flight Information Region (FIR) FRQ TS OBS AND FCST WI 200NM N3006 W14012 - N2012 W15016 CB TOP FL400 MOV W 10KT WKN. Phenomenon description The SIGMET in Figure 6-7 is decoded as the following: (Line 1) The WMO product header is WSPA07. Issued by the PHFO on the 1st day of the month at 0410 UTC. (Line 2) The NWS AWIPS communication header is SIGPAT. (Line 3) For the Oakland (KZOA) Area Control Center. This is the 2nd issuance of SIGMET Tango series, valid from the 1st day of the month at 0410 UTC until the 1st day of the month at 0800 UTC, issued by the Honolulu Meteorological Watch Office. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-16 ### Page 188 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (Line 4) Concerning the Oakland Oceanic Flight Information Region (FIR), frequent thunderstorms observed and forecast within 200 nautical miles of 30 degrees and 6 minutes north; 140 degrees and 12 minutes west; to 20 degrees and 12 minutes north, 150 degrees and 16 minutes west, cumulonimbus tops to flight level 400 moving west at 10 knots, weakening. 6.1.5.4 SIGMETs for Volcanic Ash A SIGMET for volcanic ash cloud is issued for volcanic eruptions. A volcanic eruption is any volcanic activity including the emission of volcanic ash, regardless of the eruption’s magnitude. Initial Volcanic Ash SIGMETs may be issued based on credible pilot reports in the absence of a Volcanic Ash Advisory (VAA), but are updated once a VAA is issued. Volcanic ash SIGMETs will continue to be issued until the ash cloud is no longer occurring or expected to occur over the area of responsibility. SIGMETs for volcanic ash cloud are valid up to six (6) hours and provide an observed or forecast location of the ash cloud at the beginning of the SIGMET. A six-hour forecast position for the ash cloud, valid at the end of the validity period of the SIGMET message, is also included. SIGMETs are reissued at least every six (6) hours while the volcanic ash cloud hazard exists or is expected to exist. 6.1.5.5 SIGMETs for Tropical Cyclone A SIGMET for a tropical cyclone may be issued for non-frontal synoptic-scale cyclones meeting the following criteria. • Originates over tropical or sub-tropical waters with organized convection and definite cyclonic surface wind circulation. • Wind speeds reach 35 knots independent of the wind averaging time used by the Tropical Cyclone Advisory Center (TCAC). SIGMETs for tropical cyclones will be valid up to six (6) hours. SIGMETs for tropical cyclones will include two positions. The first position included will be the TCAC advisory position. The second position will be the forecast position valid at the end of the SIGMET period. In addition to the two storm positions, SIGMETs will include associated convection when applicable. SIGMETs will be reissued at least every six (6) hours while the tropical cyclone wind remains or are expected to remain above 34 knots. 6.1.5.6 SIGMET Cancellation– Outside the Conterminous U.S. (O-CONUS) SIGMETs are cancelled when the phenomena is no longer occurring or expected to occur in the area of responsibility. 6.1.5.7 SIGMET Amendments– Outside the Conterminous U.S. (O-CONUS) SIGMET amendments will NOT be issued. Instead, the next SIGMET in the series is issued to accomplish the update. The valid time of the new SIGMET is reset to reflect the new 4-hour valid period (6-hour for VA and TC SIGMETs). 6.1.5.8 SIGMET Corrections– Outside the Conterminous U.S. (O-CONUS) Corrections to SIGMETs are issued as necessary. This is done by issuing a new SIGMET in the series which advances the SIGMET number and cancels the previous SIGMET. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-17 ### Page 189 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.1.5.9 SIGMET Example– Outside the Conterminous U.S. (O-CONUS) WSPA07 PHFO 010358 SIGPAT KZOA SIGMET TANGO 1 VALID 010400/010800 PHFO- OAKLAND OCEANIC FIR. EMBD TS OBS BY SATELLITE WITHIN AREA BOUNDED BY N2055 W15000 - N1950 W14945 - N1922 W15130 - N2027 W15048 – N2055 W15000. CB TO TOP FL400. MOV W 10KT. WKN. SIGMET (SWPA07) issued by the Meteorological Watch Office (Weather Forecast Office) in Honolulu, Hawaii (PHFO) on the 1st day of the month at 0358 UTC. The National Weather Service AWIPS communication header for this product is SIGPAT. This SIGMET concerns the Oakland Oceanic FIR. This is the first (1) issuance of SIGMET series Tango valid from the 1st day of the month at 0400 UTC until the 1st day of the month at 0800 UTC. Within the WFO Honolulu portion of the Oakland Oceanic FIR, embedded thunderstorms observed by satellite within an area bounded by 20 degrees/55 minutes north, 150 degrees/00 minutes west to 19 degrees/50 minutes north, 14 degrees/45 minutes west to 19 degrees/22 minutes north, 151 degrees/30 minutes west to 20 degrees/27 minutes north, 150 degrees/48 minutes west to 20 degrees/55 minutes north, 150 degrees/00 minutes west. Cumulonimbus tops to flight level 400 (approximately 40,000 feet MSL). The thunderstorms are moving west at 10 knots and weakening. 6.1.5.9.1 SIGMET for Volcanic Ash Example WVNT06 KKCI 082030 TJZS SIGMET FOXTROT 2 VALID 082030/090230 KKCI- SAN JUAN FIR VA FROM SOUFRIERE HILLS LOC 1642N06210W VA CLD OBS AT 2030Z SFC/060 WI N1730 W06400 - N1700 W06300 - N1650 W06300 - N1710 W06400 - N1730 W06400. MOV W 15KT. FCST 0230Z VA CLD APRX N1730 W06500 - N1700 W06300 - N1650 W06300 - N1710 W06500 - N1730 W06500. The ICAO communication header for this product is WVNT06. It is a SIGMET issued by the Aviation Weather Center (KCCI) in Kansas City, Missouri on the 8th day of the month at 2030 UTC. This is the second (2) issuance of SIGMET series Foxtrot valid from the 8th day of the month at 2030 UTC until the 9th day of the month at 0230 UTC. Within the San Juan Oceanic FIR, volcanic ash from Soufriere Hills volcano located at 16 degrees/42 minutes north, 62 degrees/10 minutes west. Volcanic ash cloud observed at 2030 UTC from the surface to 6,000 feet MSL within an area bounded by 17 degrees/30 minutes north, 64 degrees/00 minutes west to 17 degrees/00 minutes north, 63 degrees/00 minutes west to 16 degrees/50 minutes north, 63 degrees/00 minutes west to 17 degrees/10 minutes north, 64 degrees/00 minutes west to 17 degrees/30 minutes north, 64 degrees/00 minutes west. Moving to the west at 15 knots. Forecast at 0230 UTC, volcanic ash cloud located approximately at 17 degrees/30 minutes north, 65 degrees/00 minutes west to 17 degrees/00 minutes north, 63 degrees/00 minutes west to 16 degrees/50 minutes north, 63 degrees/00 minutes west to 17 degrees/10 minutes north, 65 degrees/00 minutes west to 17 degrees/30 minutes north, 65 degrees/00 minutes west. 6.1.5.9.2 SIGMET for Tropical Cyclone Example WSNT03 KKCI 081451 SIGA0C AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-18 ### Page 190 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) KZNY SIGMET CHARLIE 11 VALID 081500/082100 KKCI- NEW YORK OCEANIC FIR TC KYLE OBS N3106 W07118 AT 1500Z CB TOP FL500 WI 120NM OF CENTER MOV WSW 5 KT NC FCST 2100Z TC CENTER N3142 W07012 The ICAO communication header for this product is WSNT03. It is a SIGMET issued by the Aviation Weather Center (KCCI) in Kansas City, Missouri on the 8th day of the month at 1451 UTC. The National Weather Service AWIPS communication header for this product is SIGPAT. This is the eleventh (11) issuance of SIGMET series Charlie valid from the 8th day of the month at 1500 UTC until the 8th day of the month at 2100 UTC. Within the New York Oceanic FIR, Tropical Cyclone Kyle observed at 31 degrees/6 minutes north, 71 degrees/18 minutes west at 1500 UTC, cumulonimbus tops to flight level 500 (approximately 50,000 feet MSL), within 120 nautical miles of the center, moving from west-southwest at 5 knots, no change in intensity is forecast, at 2100 UTC the tropical cyclone center will be at 31 degrees/42 minutes north, 70 degrees/12 minutes west. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-19 ### Page 191 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.2 Airmen’s Meteorological Information (AIRMET) An AIRMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena which may affect the safety of aircraft operations, but at intensities lower than those which require the issuance of a SIGMET. AIRMETs are intended for dissemination to all pilots in flight to enhance safety and are of particular concern to operators and pilots of aircraft sensitive to the phenomena described and to pilots without instrument ratings. AIRMETs are issued by the responsible Meteorological Watch Office (MWO) to give notice to operators and aircrews of potentially hazardous en route conditions. • AIRMETs are available for the conterminous U.S. (CONUS) on the Aviation Digital Data Service (ADDS) web site at: http://adds.aviationweather.noaa.gov/airmets/ • AIRMETs are available for Alaska on the Alaska Aviation Weather Unit (AAWU) web site at: http://aawu.arh.noaa.gov/ • AIRMETs are available for Hawaii on the NWS WFO Honolulu web site at: http://www.prh.noaa.gov/hnl/pages/aviation.php 6.2.1 AIRMET Issuance AIRMETs are issued from the three Meteorological Watch Offices (MWO) located at the Aviation Weather Center (AWC), the Alaska Aviation Weather Unit (AAWU), and the Weather Forecast Office (WFO) in Honolulu. Their areas of responsibility are: • AWC: The conterminous U.S. and adjacent coastal waters (CONUS) (Figure 6-8) • AAWU: Alaska and adjacent coastal waters (Figure 6-9) • WFO Honolulu: Hawaii and adjacent waters (Figure 6-10) AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-20 ### Page 192 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-8 AWC AIRMET Areas of Responsibility – Conterminous U.S. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-21 ### Page 193 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-9. AAWU Flight Advisory and Area Forecast Zones - Alaska Table 6-4. AAWU Flight Advisory and Area Forecast Zones – Alaska 1 Arctic Coast Coastal 14 Southern Southeast Alaska 2 North Slopes of the Brooks Range 15 Coastal Southeast Alaska 3 Upper Yukon Valley 16 Eastern Gulf Coast 4 Koyukuk and Upper Kobuk Valley 17 Copper River Basin 5 Northern Seward Peninsula-Lower Kobuk Valley 18 Cook Inlet-Susitna Valley 6 Southern Seward Peninsula-Eastern Norton Sound 19 Central Gulf Coast 7 Tanana Valley 20 Kodiak Island 8 Lower Yukon Valley 21 Alaska Peninsula-Port Heiden to Unimak Pass 9 Kuskowim Valley 22 Unimak Pass to Adak 10 Yukon-Kuskowim Delta 23 St. Lawrence Island-Bering Sea Coast 11 Bristol Bay 24 Adak to Attu 12 Lynn Canal and Glacier Bay 25 Pribilof Islands and Southeast Bering Sea 13 Central Southeast Alaska AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-22 ### Page 194 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-10. WFO Honolulu AIRMET Areas of Responsibility - Hawaii 6.2.2 AIRMET Issuance Criteria An AIRMET may be issued when any of the following weather phenomena are occurring or expected to occur over an area of at least 3,000 square miles: • Ceiling less than 1,000 feet and/or visibility less than 3 statute miles (IFR) o Weather phenomena restricting the visibility including, but not limited to, precipitation (PCPN), smoke (FU), haze (HZ), mist (BR), fog (FG), and blowing snow (BS). • Widespread mountain obscuration (MTN OBSCN) o Weather phenomena causing the obscurement are included, but limited to clouds (CLDS), precipitation (PCPN), smoke (FU), haze (HZ), mist (BR), and fog (FG). • Moderate turbulence (MOD TURB) o Top and bottom of MOD TURB layer are specified. • Sustained surface wind greater than 30 knots (STG SFC WND) • Moderate icing (MOD ICE) AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-23 ### Page 195 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) o Top and bottom of MOD ICE are specified. o The range of freezing level altitudes is given when the bottom altitude of MOD ICE is the freezing level (FRZLVL). o Areas with multiple freezing levels are specified. o Range of freezing levels over the area is specified. o Lowest freezing levels above ground level (AGL) at intervals of 4,000 feet AMSL (or SFC as appropriate) are specified. • Non-convective low-level wind shear potential below 2,000 feet AGL (LLWS POTENTIAL). 6.2.3 AIRMET Standardization All AIRMETs follow these standards: • All heights or altitudes are referenced to above mean sea level (AMSL), unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 feet, the level is preceded by FL to represent flight levels (e.g., FL180). • Messages are prepared in abbreviated plain language using contractions from the Federal Aviation Administration (FAA) Order 7340.1Z. A limited number of nonabbreviated words, geographical names and numerical values of a self-explanatory nature may also be used. • Weather and obstructions to visibility are described using the weather abbreviations for surface weather observations (METAR/SPECI). See the Federal Meteorological Handbook (FMH) No. 1 – Surface Observations or Section 3.1 of this document. Note: Refer to Appendix A for definitions of common terms used in AIRMETs. 6.2.4 AIRMET Bulletins, Issuance Times, and Valid Period AIRMETs are issued as bulletins containing one or more AIRMET messages following the schedule listed below. Unscheduled AIRMETs are issued when conditions are occurring or expected to occur, but were not forecast. Table 6-5. AIRMET Issuance Schedule 1st Scheduled Issuance (UTC) 2nd Scheduled Issuance (UTC) 3rd Scheduled Issuance (UTC) 4th Scheduled Issuance (UTC) CONUS 0245 0845 1445 2045 Alaska 0145 (DT)/ 0245 (ST) 0745 (DT)/ 0845 (ST) 1345 (DT)/ 1445 (ST) 1945 (DT)/ 2045 (ST) Hawaii 0400 1000 1600 2200 Note: DT - Daylight Time, ST - Standard Time AIRMETs are valid for no more than 6 hours. The valid period of an AIRMET message cannot exceed the valid time of the AIRMET bulletin. However, note that each AIRMET contains remarks concerning the continuance of the phenomenon during the six (6) hours following the AIRMET ending time. Also, AIRMET bulletins can contain a separate outlook when conditions AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-24 ### Page 196 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) meeting AIRMET criteria are expected to occur during the 6-hour period after the valid time of the AIRMET bulletin. 6.2.5 AIRMET Format An AIRMET message includes the following information as appropriate and in the order indicated: • Reference to appropriate active SIGMETs affecting the area at the time of AIRMET issuance (e.g., SEE SIGMET BRAVO SERIES). • Beginning time of the AIRMET phenomenon if different from the AIRMET beginning valid time. • AIRMET name (SIERRA, TANGO or ZULU), update number, weather phenomenon, and ending valid time (Note: the AIRMET number is reset to one (1) after 0000 UTC each day). o AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations o AIRMET Tango describes moderate turbulence, sustained surface winds of 30 knots or greater and non-convective low-level wind shear. o AIRMET Zulu describes moderate icing and provides freezing level heights • List of affected states (CONUS only). • Location of phenomenon using VORs or other well known geographic features. • Description of phenomenon for the AIRMET issuance. • Vertical extent (bases and tops), as appropriate. • Ending time of phenomenon if different from the AIRMET ending time. • Remarks concerning the continuance of the phenomenon during the six (6) hours following the AIRMET ending time. • CONUS and Hawaii AIRMETs: A separate AIRMET outlook is included in the AIRMET bulletin when conditions meeting AIRMET criteria are expected to occur during the 6- hour period after the valid time of the AIRMET bulletin. • Alaska AIRMETs: Outlook information is included in the appropriate Area Forecast zone when conditions are expected to occur during the 6-hour period after the valid time of the AIRMET bulletin. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-25 ### Page 197 (OCR) Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) LINE 1 BOSS WA 211945 2 AIRMET SIERRA UPDT 3 FOR IFR AND MIN OBSCN VALID UNTIL 220200 ЗА AIRMET IFR..ME NH VT MA CT RI NY NJ AND CSTL WTRS 4A FROM CAR TO YSJ TO 150E ACK TO EWR TO YOW TO CAR SA OCNL CIG BLW 010/VIS BLW 3SM PCPN/BR. CONDS CONT BYD 02Z THRU 082. ЗВ AIRMET MIN OBSCN..ME NH VT MA NY PA 4B FROM CAR TO MLT TO CON TO SLT TO SYR TO CAR 5B MINS ONLY OBSCD BY CLDS/PCPN/BR. CONDS CONT BYD 02Z THRU 08Z. Figure 6-11. AIRMET Bulletin Decoding Example Table 6-6. Decoding an AIRMET Bulletin Line Content Description 1 BOS AIRMET area identifier S AIRMET series WA Product type 211945 Issuance UTC date/time 2 AIRMET Product type SIERRA AIRMET series UPDT 3 Update number FOR IFR AND MTN OBSCN Product description VALID UNTIL 220200 Ending UTC date/time ЗА AIRMET IFR..ME NH VI MA CT RI NY Product type/series... NJ AND CSTL WTRS Phenomenon location ЗВ AIRMET MIN OBSCN..ME NH VT MA NY (states) 4A FROM CAR TO YSJ TO 150E ACK TO EWR Phenomenon location TO YOW TO CAR (VOR locations) 4B FROM CAR TO MLT TO CON TO SIT TO SYR TO CAR 5A CIG BLW 010/VIS BLW 3SM PCPN/BR. Phenomenon description CONDS CONT BYD 02Z THRU 08Z. **5B MINS OBSCD BY CLDS/PCPN/BR. CONDS CONT BYD 02Z THRU 08Z.** The AIRMET bulletin in Figure 6-11 is decoded as follows: (Line 1) AIRMET SIERRA issued for the Boston area at 1945Z on the 21s day of the month. "SIERRA" contains information on Instrument Flight Rules (IFR) and/or mountain obscurations. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-26 ### Page 198 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (Line 2) This is the third updated issuance of this Boston AIRMET series as indicated by “SIERRA UPDT 3” and is valid until 0200Z on the 22nd. (Line 3A) The affected states within the BOS area are: Maine, New Hampshire, Vermont, Massachusetts, Connecticut, Rhode Island, New York, New Jersey, and coastal waters. (Line 3B) The affected states within the BOS area are: Maine, New Hampshire, Vermont, Massachusetts, New York, and Pennsylvania. (Line 4A) Within an area bounded by: Caribou, ME; to Saint Johns, New Brunswick; to 150 nautical miles east of Nantucket, MA; to Newark, NJ; to Ottawa, Ontario; to Caribou, ME (Line 4B) Within an area bounded by: Caribou, ME to Millinocket, ME to Concord, NH to Slate Run, PA to Syracuse, NY to Caribou, ME (Line 5A) Ceiling below 1,000 feet/visibility below 3 statute miles, precipitation/mist. Conditions continuing beyond 0200Z through 0800Z. (Line 5B) Mountains Obscured by clouds, precipitation and mist. Conditions continuing beyond 0200Z through 0800Z. 6.2.5.1 AIRMET Updates and Amendments If an AIRMET is amended, AMD is added after the date/time group on the FAA product line. The update number will be incremented, UPDT is added to end of the line containing the list of affected states (CONUS only). The issuance time of the AIRMET bulletin is updated to reflect the time of the amendment. The ending valid time remains unchanged. 6.2.5.2 AIRMET Corrections AIRMETs containing errors are corrected by adding COR after the date/time group on the FAA product line. The issuance time of the AIRMET bulletin is updated to reflect the time of the correction. The ending valid time remains unchanged. 6.2.6 AIRMET Examples 6.2.6.1 CONUS AIRMET Example WAUS43 KKCI 091445 CHIZ WA 091445 AIRMET ZULU UPDT 4 FOR ICE AND FRZLVL VALID UNTIL 092100 AIRMET ICE...KS IA MO IL FROM 30WSW FOD TO DBQ TO 50NW DEC TO 50SW FAM TO OSW TO MKC TO 30WSW FOD MOD ICE BTN FRZLVL AND FL200. FRZLVL 060-100. CONDS ENDG BY 21Z. . OTLK VALID 2100-0300Z...ICE IA MO WI IL IN KY BOUNDED BY BAE-BVT-PXV-50SW FAM-50NW DEC-DBQ-BAE MOD ICE BTN FRZLVL AND FL200. FRZLVL 080-100. CONDS CONTG THRU 03Z. . FRZLVL...RANGING FROM SFC-120 ACRS AREA MULT FRZLVL 015-085 BOUNDED BY 40W INL-YQT-SSM-70NNE AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-27 ### Page 199 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) ASP-YVV-DXO-40NE FWA-40SSE BJI-40W INL SFC ALG 50NNW ISN-70W FAR-GFK-40NE ODI-40SW DXO 040 ALG ISN-70S BIS-30W ABR-30E ABR-60S FAR-30SW BRD-30NE FWA 080 ALG GLD-SLN-30W BDF-50S JOT-40SE IND-30SW CVG-40SW LOZ AIRMET (WAUS43) issued by the Meteorological Watch Office (Aviation Weather Center) in Kansas City, Missouri on the 9th day of the month at 1445 UTC. This AIRMET (WA) is the Zulu series bulletin for the Chicago Area Forecast region (CHIZ) issued on the 9th day of the month at 1445 UTC. This is the 4th update to the Zulu series bulletin for icing and freezing levels and is valid until the 9th day of the month at 2100 UTC. The first (and only) AIRMET noted within the bulletin is for icing affecting Kansas, Iowa, Missouri and Illinois. Within an area bounded from 30 nautical miles west-southwest of Fort Dodge, Iowa (FOD) to Dubuque, Iowa (DBQ) to 50 nautical miles northwest of Decatur, Illinois (DEC) to 50 nautical miles southwest of Farmington, Missouri (FAM) to Oswego, Kansas (OSW) to Kansas City, Missouri (MKC) to 30 nautical miles west-southwest of Fort Dodge, Iowa (FOD). Moderate icing between the freezing level and flight level 200 (approximately 20,000 feet MSL). The freezing level is between 6,000 feet MSL and 10,000 feet MSL. Conditions ending by 2100 UTC. An outlook for icing between 2100 UTC to 0300 UTC exists over: Iowa, Missouri, Wisconsin, Illinois, Indiana and Kentucky. Within an area bounded by Milwaukee, Wisconsin (BAE) to Lafayette, Indiana (BVT) to Pocket City, Indiana (PXV) to 50 nautical miles southwest of Farmington, Missouri (FAM) to 50 nautical miles northwest of Decatur, Illinois (DEC) to Dubuque, Iowa (DBQ) to Milwaukee, Wisconsin (BAE). Moderate icing between the freezing level and flight level 200 (approximately 20,000 feet MSL). The freezing level is between 8,000 feet MSL and 10,000 feet MSL. Conditions continuing through 0300 UTC. The freezing level ranges from the surface to 12,000 feet MSL across the Chicago Area Forecast region. Multiple freezing levels exist between 1,500 feet MSL and 8,500 feet MSL within an area bounded by 40 nautical miles west of International Falls, Minnesota (INL) to Thunder Bay, Ontario, Canada to Sault Saint Marie, Michigan (SSM) to 70 nautical miles northnortheast of Oscoda, Michigan (ASP) to Wiarton, Ontario, Canada to Detroit, Michigan (DXO) to 40 nautical miles northeast of Fort Wayne, Indiana (FWA) to 40 nautical miles south-southeast of Bemidji, Minnesota (BJI) to 40 nautical miles west of International Falls, Minnesota (INL). The freezing level is at the surface along a line from 50 nautical miles north-northwest of Williston, North Dakota (ISN) to 70 nautical miles west of Fargo, North Dakota (FAR) to Grand Forks, North Dakota (GFK) to 40 nautical miles northeast of Nodine, Minnesota (ODI) to 40 nautical miles southwest of Detroit, Michigan (DXO). The freezing level is at 4,000 feet MSL along a line from Williston, North Dakota (ISN) to 70 nautical miles south of Bismarck, North Dakota (BIS) to 30 nautical miles west of Aberdeen, South Dakota (ABR) to 30 nautical miles east of Aberdeen, South Dakota (ABR) to 60 nautical miles south of Fargo, North Dakota (FAR) to 30 nautical miles southwest of Brainerd, Minnesota (BRD) to 30 nautical miles northeast of Fort Wayne, Indiana. The freezing level is 8,000 feet MSL along a line from Goodland, Kansas (GLD) to Salina, Kansas (SLN) to 30 nautical miles west of Bradford, Illinois (BDF) to 50 nautical miles south of Joliet, Illinois to 40 nautical miles southeast of Indianapolis, Indiana (IND) to 30 nautical miles southwest of Covington, Kentucky (CVG) to 40 nautical miles southwest of London, Kentucky (LOZ). 6.2.6.2 Hawaii AIRMET Example AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-28 ### Page 200 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) WAHW31 PHFO 090945 WA0HI HNLT WA 091000 AIRMET TANGO UPDATE 1 FOR TURB VALID UNTIL 091600 AIRMET TURB...KAUAI OAHU MOLOKAI LANAI MAUI OVR AND IMDT N THRU E OF MTS. **MOD TURB BLW 100. CONDS CONTG BYD 1600Z.** AIRMET (WAHW31) issued by the Meteorological Watch Office (Weather Forecast Office) in Honolulu, Hawaii on the 9th day of the month at 0945 UTC. The National Weather Service AWIPS communication code for this product is WA0HI. This AIRMET (WA) is the Tango series bulletin for the Hawaii Area Forecast region (HNLT) issued on the 9th day of the month at 1000 UTC. This is the 1st update to the Tango series bulletin for turbulence and is valid until the 9th day of the month at 1600 UTC. The first (and only) AIRMET noted within the bulletin is for turbulence affecting the islands of Kauai, Oahu, Molokai, Lanai and Maui, over and immediately north through east of the mountains. Moderate turbulence below 10,000 feet MSL. Conditions continuing beyond 1600 UTC. 6.2.6.3 Alaska AIRMET Example WAAK47 PAWU 011740 WA7O JNUS WA 011740 AIRMET SIERRA FOR IFR AND MT OBSC VALID UNTIL 012100 . **LYNN CANAL AND GLACIER BAY JB W OF LYNN CANAL..MTS OCNL OBSC IN CLDS/PCPN.** **SPRDG E. INTSF.** . CNTRL SE AK JC PAOH−PAFE LN W..MTS OCNL OBSC IN CLDS/PCPN. SPRDG E. INTSF. . **ERN GLF CST JE MTS OCNL OBSC IN CLDS/PCPN. IMPRG.** . **SE AK CSTL WTRS JF OCNL CIG BLW 010 VIS BLW 3SM SN BLSN. NC.** AIRMET (WAAK47) issued by the Meteorological Watch Office (Alaska Aviation Weather Unit) in Anchorage, Alaska on the 1st day of the month at 1740 UTC. The National Weather Service AWIPS communication code for this product is WA7O. This AIRMET (WA) is the Sierra series bulletin for the Juneau forecast area issued on the 1st day of the month at 1740 UTC. This is the AIRMET Sierra series for IFR and mountain obscuration valid until the 1st day of the month at 2100 UTC. For the Lynn Canal and Glacier Bay forecast regions, Juneau region B...west of Lynn Canal…mountains occasionally obscured in clouds and precipitation. Conditions spreading east and intensifying during the forecast period. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-29 ### Page 201 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) For the Central Southeast Alaska forecast region, Juneau region C…from a Hoonan, Alaska (PAOH) to Kake, Alaska (PAFE) line westward, mountains occasionally obscured in clouds and precipitation. Conditions spreading east and intensifying during the forecast period. For the Eastern Gulf Coast forecast region, Juneau region E…Mountains occasionally obscured in clouds and precipitation. Conditions improving during the forecast period. For the Southeast Alaska Coastal Waters, Juneau region F…Occasional ceiling below 1,000 feet AGL, visibility below 3 statute miles in snow and blowing snow. No change in conditions is expected during the forecast period. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-30 ### Page 202 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.3 Center Weather Advisory (CWA) A Center Weather Advisory (CWA) is an aviation weather warning for conditions meeting or approaching national in-flight advisory (AIRMET, SIGMET or Convective SIGMET) criteria. The CWA is primarily used by aircrews to anticipate and avoid adverse weather conditions in the en route and terminal environments. CWAs are available on the Aviation Weather Center (AWC) web site at: http://aviationweather.gov/products/cwsu/. 6.3.1 CWA Issuance CWAs are issued by the NWS Center Weather Service Units (CWSUs). CWSU areas of responsibility in the contiguous U.S. are depicted on Figure 6-12. CWSU Anchorage area of responsibility for Alaska is depicted on Figure 6-13. Figure 6-12. Center Weather Service Unit (CWSU) Areas of Responsibility, Contiguous U.S. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-31 ### Page 203 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-13. CWSU Anchorage, AK (PAZA) Area of Responsibility CWAs are valid for up to two (2) hours and may include forecasts of conditions expected to begin within two (2) hours of issuance. If conditions are expected to persist after the advisory’s valid period, a statement to that effect is included in the last line of the text. Additional CWAs will subsequently be issued as appropriate. Notice of significant changes in the phenomenon described in a CWA is provided by a new CWA issuance for that phenomenon. If the forecaster deems it necessary, CWAs may be issued hourly for convective activity. 6.3.2 CWA Communications Headers (UCWA / CWA) The Urgent CWA (UCWA) communications header is intended for those situations where weather conditions have an immediate effect on the safe flow of air traffic within the ARTCC area of responsibility. It is only used when the CWSU meteorologist believes any delay in dissemination to FAA facilities would impact aviation safety. The routine CWA header is used for subsequent issuances of the same phenomenon. 6.3.3 CWA Criteria CWAs are used in the four (4) following situations: • Precede an Advisory o When the AWC has not yet issued an advisory, but conditions meet or will soon meet advisory criteria. o In the case of an impending advisory, the CWA can be issued as an Urgent CWA (UCWA) to allow the fastest possible dissemination. • Refine an existing Advisory o To supplement an existing AWC advisory for the purpose of refining or updating the location, movement, extent, or intensity of the weather event relevant to the ARTCC’s area of responsibility. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-32 ### Page 204 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) • Highlight significant conditions not meeting Advisory criteria o When conditions do not meet advisory criteria, but conditions, in the judgment of the CWSU meteorologist, will adversely impact air traffic within the ARTCC area of responsibility. • To cancel a CWA when the phenomenon described in the CWA is no longer expected. 6.3.4 CWA Format Figure 6-14. Center Weather Advisory (CWA) Decoding Example Table 6-7. Decoding a Center Weather Advisory (CWA) Line Content Description 1 ZDV ARTCC Identification 2 Phenomenon Number (single digit, 1-6) CWA Product Type (UCWA/CWA) 032140 Beginning and/or issuance UTC date/time 2 ZDV ARTCC Identification CWA Product Type 2 Phenomenon Number (single digit, 1-6) 02 Issuance Number (issued sequentially for each Phenomenon Number) VALID TIL 032340Z Ending valid UTC date/time 3 FROM FMN TO 10N FMN TO 20NE FMN TO 10E FMN TO FMN Phenomenon Location 4 ISOLD SEV TS NR FMN MOVG NEWD 10KTS. TOP FL410. WND GSTS TO 55KTS. HAIL TO 1 INCH RPRTD AT FMN. SEV TS CONTG BYD 2340Z Phenomenon Description AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-33 ### Page 205 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Time permitting, any CWA overlapping into another center's airspace is coordinated and a statement is included in the text, e.g., SEE ZOB CWA 201 FOR TS CONDS IN ZOB CTA (CTA is control area). If issuance prior to coordination is necessary, a statement regarding the area(s) affected is included in the text, e.g., LINE TS EXTDS NW INTO ZOB CTA. AIRMETs/SIGMETs being augmented by the CWA will be referenced in a text remark, e.g. **SEE CONVECTIVE SIGMET 8W.** The CWA in Figure 6-14 is decoded as follows: (Line 1) Center Weather Advisory issued for the Denver ARTCC (ZDV) CWSU. The “2” after ZDV in the first line denotes this is the second meteorological event of the local calendar day. This CWA was issued/begins on the 3rd day of the month at 2140 UTC. (Line 2) The Denver ARTCC (ZDV) is identified again. The “202” in the second line denotes the phenomena number again (2) and the issuance number (02) for this phenomenon. This CWA is the valid until the 3rd day of the at 2340 UTC. (Line 3) From Farmington, New Mexico to 10 nautical miles north of Farmington, New Mexico to 20 nautical miles northeast of Farmington, NM to 10 nautical mile east of Farmington, New Mexico to Farmington, New Mexico. (Line 4) Isolated severe thunderstorms near Farmington moving northeastward at 10 knots. Tops to Flight Level 410. Wind gusts to 55 knots. Hail to one inch reported at Farmington. Severe thunderstorms continuing beyond 2340 UTC. 6.3.5 Examples **ZME1 CWA 081300** **ZME CWA 101 VALID TIL 081500** **FROM MEM TO JAN TO LIT TO MEM OCNL TS MOV FM 26025KT. TOPS TO FL450.** Center Weather Advisory issued for the Memphis, Tennessee ARTCC on the 8th day of the month at 1300 UTC. The 1 after the ZME in the first line denotes this CWA has been issued for the first weather phenomenon to occur for the local calendar day. The 101 in the second line denotes the phenomenon number again (1) and the issuance number (01) for this phenomenon. The CWA is valid until the 8th of the month at 1500 UTC. From Memphis, Tennessee to Jackson, Mississippi to Little Rock, Arkansas to Memphis, Tennessee. Occasional thunderstorms moving from 260 degrees at 25 knots. Tops to flight level 450. **ZLC3 CWA 271645** **ZLC CWA 303 VALID TIL 271745 CNL CWA 302.** **SEE CONVECTIVE SIGMET 8W.** Center Weather Advisory issued for the Salt Lake City, Utah ARTCC on the 27th day of the month at 1645 UTC. The 3 after the ZLC in the first line denotes this CWA has been issued for the third weather phenomenon to occur for the local calendar day. The 303 in the second line AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-34 ### Page 206 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) denotes the phenomenon number again (3) and the issuance number (03) for this phenomenon. The CWA is valid until the 27th day of the month at 1745 UTC. CWA number 302 has been cancelled. See Convective SIGMET 8W. **ZME1 CWA 040100** **ZME CWA 101 VALID TIL 040300** VCY MEM SEV CLR ICE BLW 020 DUE TO FZRA. NUMEROUS ACFT REP RAPID ACCUMULATION OF ICE DRG DES TO MEM. NO ICE REPS ABV 020. CONDS CONTG AFT 03Z. NO UPDATES AFT 040200Z. Center Weather Advisory issued for the Memphis, Tennessee ARTCC on the 4th day of the month at 0100 UTC. The 1 after the ZLC in the first line denotes this CWA has been issued for the first weather phenomenon to occur for the local calendar day. The 101 in the second line denotes the phenomenon number again (1) and the issuance number (01) for this phenomenon. The CWA is valid until the 4th day of the month at 0300 UTC. For the Memphis, Tennessee vicinity. Severe clear icing below 2,000 feet MSL due to freezing rain. Numerous aircraft report rapid accumulation of icing during descent to Memphis. No icing reports above 2,000 feet MSL. Conditions continuing after 0300 UTC. No updates after 4th day of the month at 0200 UTC. **ZNY5 UCWA 021400** ZNY CWA 502 VALID TIL 021600 FROM BGM TO 18WNW JFK TO HAR TO SLT TO BGM NUMEROUS ACFT REP SEV TURB AND WS BLW 020. **CONDS EXTD NE INTO ZBW CTA. CONDS EXP TO CONT AFT 16Z.** Center Weather Advisory issued for the New York ARTCC on the 2nd day of the month at 1400 UTC. The 5 after the ZNY in the first line denotes this CWA has been issued for the fifth weather phenomenon to occur for the local calendar day. The 502 in the second line denotes the phenomenon number again (5) and the issuance number (02) for this phenomenon. The CWA is valid until the 2nd day of the month at 1600 UTC. From Binghamton, New York; to 18 nautical miles west-northwest of New York (JFK Airport), New York; to Harrisburg, Pennsylvania; to Slate Run, Pennsylvania; to Binghamton, New York. Numerous aircraft report severe turbulence and wind shear below 2,000 feet MSL. Conditions extending northeast into Nashua, New Hampshire control area. Conditions expected to continue after 1600 UTC. **ZNY4 UCWA 041500** ZNY CWA 401 VALID TIL 041700 40N SLT TO 18WNW JFK DEVELOPING LINE TS 25 NM WIDE MOV 24020KT. TOPS ABV FL350. **LINE TS EXTDS NW INTO ZOB CTA.** Urgent Center Weather Advisory issued for the New York ARTCC on the 4th day of the month at 1500 UTC. The 4 after the ZNY in the first line denotes this CWA has been issued for the fourth weather phenomenon to occur for the local calendar day. The 401 in the second line denotes the phenomenon number again (4) and the issuance number (01) for this phenomenon. The AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-35 ### Page 207 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) CWA is valid until the 4th day of the month at 1700 UTC. From 40 nautical miles north of Slate Run, Pennsylvania; to 18 nautical miles west-northwest of New York (JFK Airport), New York. Developing line of thunderstorms 25 nautical miles wide moving from 240 degrees at 20 knots. Tops above flight level 350. The line of thunderstorms extends northwest into the Oberlin, Ohio control area. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-36 ### Page 208 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.4 Additional Products for Convection The National Weather Service (NWS) in addition to the SIGMETs, Convective SIGMETs, and CWAs already discussed, offers a few more products informing the aviation community about the potential for convective weather. 6.4.1 Convective Outlooks (AC) The NWS Storm Prediction Center (SPC) issues narrative and graphical convective outlooks to provide the contiguous U.S. NWS Weather Forecast Offices (WFOs), the public, media and emergency managers with the potential for severe (tornado, wind gusts 50 knots or greater, or hail 3/4 inch diameter size or greater) and non-severe (general) convection and specific severe weather threats during the following three days. The Convective Outlook defines areas of slight risk (SLGT), moderate risk (MDT) or high risk (HIGH) of severe thunderstorms for a 24-hour period beginning at 1200 UTC. The Day 1 and Day 2 Convective Outlooks also depict areas of general thunderstorms (GEN TSTMS), while the Day 1, Day 2, and Day 3 Convective Outlooks may use SEE TEXT for areas where convection may approach or slightly exceed severe criteria. The outlooks are available on the SPC web site at: http://www.spc.noaa.gov/products/outlook/. 6.4.1.1 Issuance Convective Outlooks are scheduled products issued at the following times: Table 6-8. Convective Outlook Issuance Schedule Convective Outlook Issuance Time (UTC) Valid Period (UTC) Day 1 0600 1200 – 1200 1300 1300 – 1200 1630 1630 – 1200 2000 2000 – 1200 0100 0100 – 1200 Day 2 0730 (Daylight Savings Time) 0830 (Standard Time) Day 2/1200 – 1200 1730 Day 2/1200 – 1200 Day 3 1100 Day 3/1200 – 1200 SPC corrects outlooks for format and grammatical errors and amends outlooks when the current forecast does not or will not reflect the ongoing or future convective development. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-37 ### Page 209 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-15. Day 1 Categorical Convective Outlook Graphic Example 6.4.1.2 Format of the Categorical Convective Outlook Narrative SPC AC ddhhmm [SPC - issuing office, AC – product type, ddhhmm – date and time the product was issued **DAY (ONE, TWO OR THREE) CONVECTIVE OUTLOOK** NWS STORM PREDICTION CENTER NORMAN OK time am/pm time zone day mon dd yyyy VALID DDHHMM – DDHHMMZ **THERE IS A (SLIGHT, MODERATE, HIGH) RISK OF SEVERE THUNDERSTORMS TO** THE RIGHT OF LINE (LIST OF ANCHOR POINTS AND DIRECTION AND DISTANCE IN STATUTE MILES FROM THE LINE). THE LINE WILL ENCLOSE THE AREA OF RISK. THERE MAY BE ONE OR MORE AREAS OF RISK AT THE APPROPRIATE LEVEL OF RISK. WHEN A MODERATE OR HIGH RISK IS FORECAST, THE INDIVIDUAL STATES ARE ALSO LISTED WITH THE TWO LETTER POSTAL STATE IDENTIFIERS. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM (LIST OF ANCHOR POINTS AND DIRECTION AND DISTANCE IN STATUTE MILES FROM THE LINE). THERE MAY BE ONE OR MORE AREAS OF GEN TSTMS LISTED. …AREA OF CONCERN #1… AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-38 ### Page 210 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) **AREAS OF HIGHEST RISK ARE DISCUSSED FIRST (HIGH SEVERE RISK,** MODERATE SEVERE RISK, SLIGHT SEVERE RISK, APPROACHING SEVERE LIMITS). THE FORECAST PROVIDES A NARRATIVE TECHNICAL DISCUSSION. …AREA OF CONCERN #2… **NARRATIVE TECHNICAL DISCUSSION** $$ …FORECASTER NAME… MM/DD/YY 6.4.2 Watch Notification Messages The NWS Storm Prediction Center (SPC) issues Watch Notification Messages to alert the aviation community, NWS offices (WFOs), the public, media and emergency managers to organized thunderstorms forecast to produce tornadic and/or severe weather in the conterminous U.S. SPC issues three types of Watch Notification Messages: Aviation Watch Notification Message, Public Severe Thunderstorm Watch Notification Message and Public Tornado Watch Notification Message. They are available on the SPC web site at: http://www.spc.noaa.gov/products/watch/. 6.4.2.1 Aviation Watch Notification Message SPC issues Aviation Watch Notification Messages to alert the aviation community to organized thunderstorms forecast to produce tornadic and/or severe weather as indicated in Public Watch Notification Messages. 6.4.2.1.1 Format of an Aviation Watch Notification Message SPC AWW ddhhmm WWnnnn SEVERE TSTM ST LO DDHHMMZ - DDHHMMZ AXIS...XX STATUTE MILES EITHER SIDE OF A LINE XXDIR CCC/LOCATION ST/ - XXDIR CCC/LOCATION ST ..AVIATION COORD.. XX NM EITHER SIDE /XXDIR CCC - XXDIR CCC HAIL SURFACE AND ALOFT..X X/X INCHES. WIND GUSTS..XX KNOTS. **MAX TOPS TO XXX. MEAN STORM MOTION VECTOR DIR/SPEED** AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-39 ### Page 211 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Figure 6-16. Aviation Watch Notification Message Decoding Example Table 6-9. Decoding a Severe Weather Watch Bulletin Line Content Description 1 SPC AWW 132101 Issuing office Product Type Issuance date/time 2 WW568 TORNADO OK 132130Z – 140300Z Watch number Watch Type States affected Valid date/time period 3 AXIS..80 STATUTE MILES EAST AND WEST OF A LINE... Watch axis 4 50SSE FSI/FORT SILL OK/ - 20NW PNC/PONCA CITY OK/ Anchor points 5 …AVIATION COORDS.. 70NM E/W/ 21E SPS – 43S ICT/ Aviation coordinates 6 HAIL SURFACE AND ALOFT…3 INCHES. **WIND GUSTS..70 KNOTS. MAX TOPS TO** **550. MEAN STORM MOTION VECTOR 26030.** Type, intensity, max tops, and mean storm motion using standard contractions. The Severe Weather Watch Bulletin in Figure 6-16 is decoded as follows: (Line 1) Alert Severe Weather Watch Bulletin (AWW), issued by the Storm Prediction Center on the 13th at 2101Z, (Line 2) for Tornado Watch number 568 (WW568) for Oklahoma, valid from the 13th at 2130Z until the 14th at 0300Z. (Line 3) The Tornado Watch area is along and 80 statute miles east and west of a line from (Line 4) 50 statute miles south southeast of Fort Sill (Lawton), OK to 20 statute miles northwest of Ponca City, OK. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-40 ### Page 212 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) (Line 5) Aviation coordinates for this Tornado Watch are 70 nautical miles east and west of a line from 21 nautical miles east of Sheppard AFB (Wichita Falls), TX to 43 nautical miles south of Wichita, KS. (Line 6) Hail surface and aloft to 3 inches in diameter, wind gusts to 70 knots, max tops to Flight Level 550, mean storm motion from 260 degrees at 30 knots 6.4.2.1.2 Issuance Watch Notification Messages are non-scheduled, event driven products valid from the time of issuance to expiration or cancellation time. Valid times are in UTC. SPC will correct watches for format and grammatical errors. When tornadoes or severe thunderstorms have developed, the local NWS Weather Forecast Offices (WFOs) will issue the warnings for the storms. SPC forecasters may define the watch area as a rectangle (some number of miles either side of line from point A to point B) or as a parallelogram (some number of miles north and south or east and west of line from point A to point B). The axis coordinates are measured in statute miles. The aviation coordinates are measured in nautical miles and referenced to VHF Omni- Directional Range (VOR) navigational aid locations. The watch half-width is in statute miles. The Aviation Watch Notification Message contains hail size in inches or half inches at the surface and aloft, surface convective wind gusts in knots, maximum tops, and the Mean Storm Motion Vector. Forecasters have discretion in including hail size for tornado watches associated with hurricanes. 6.4.3 Public Severe Thunderstorm Watch Notification Message SPC issues a Public Severe Thunderstorm Watch Notification Message when forecasting six or more hail events of 3/4 inch (penny) diameter or greater or damaging winds of 50 knots (58 mph) or greater. The forecast event minimum threshold is at least 2 hours over an area at least 8,000 square miles. Below these thresholds, SPC, in collaboration with affected NWS offices may issue convective watches along coastlines, near the Canadian and Mexican borders, and for any ongoing organized severe convection. A Public Severe Thunderstorm Watch Notification Message contains the area description and axis, watch expiration time, a description of hail size and thunderstorm wind gusts expected, the definition of the watch, a call to action statement, a list of other valid watches, a brief discussion of meteorological reasoning, and technical information for the aviation community. SPC includes the term “adjacent coastal waters” when the watch affects coastal waters adjacent to the Pacific/Atlantic coast, Gulf of Mexico, or Great Lakes. Adjacent coastal waters refers to a WFO’s near-shore responsibility (out to 20 miles for oceans), except for convective watches which include portions of the Great Lakes. SPC issues a watch cancellation message when no counties, parishes, independent cities and/or marine zones remaining are in the watch area prior to the expiration time. The text of the message will specify the number and area of the cancelled watch. 6.4.3.1 Format of Public Severe Thunderstorm Watch Notification Message WWUS20 KWNS ddhhmm (ICAO communication header) AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-41 ### Page 213 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER nnnn NWS STORM PREDICTION CENTER NORMAN OK time am/pm time zone day mon dd yyyy **THE STORM PREDICTION CENTER HAS ISSUED A** **SEVERE THUNDERSTORM WATCH FOR PORTIONS OF** **PORTION OF STATE** **PORTION OF STATE** **AND ADJACENT COASTAL WATERS (IF REQUIRED)** EFFECTIVE (TIME PERIOD) UNTIL hhmm am/pm time zone. ...THIS IS A PARTICULARLY DANGEROUS SITUATION (IF FORECAST)... HAIL TO X INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO XX MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS. NARRATIVE DESCRIPTION OF WATCH AREA USING A LINE AND ANCHOR POINTS. DISTANCES TO EITHER SIDE OF THE LINE WILL BE IN STATUTE MILES. **CALL TO ACTION STATEMENTS** OTHER WATCH INFORMATION...OTHER WATCHES IN EFFECT AND IF THIS WATCH REPLACES A PREVIOUS WATCH. **NARRATIVE DISCUSSION OF REASON FOR THE WATCH.** **AVIATION...BRIEF DESCRIPTION OF SEVERE WEATHER THREAT TO AVIATORS.** HAIL SIZE WILL BE GIVEN IN INCHES AND WIND GUSTS IN KNOTS. MAXIMUM STORM TOPS AND A MEAN STORM VECTOR WILL ALSO BE GIVEN. $$ ..FORECASTER NAME.. MM/DD/YY 6.4.3.2 Example of a Public Severe Thunderstorm Watch Notification Message WWUS20 KWNS 161711 (ICAO communication header) SPC WW 161710 **URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 647** **NWS STORM PREDICTION CENTER NORMAN OK 1210 PM CDT FRI JUL 16 2004** **THE NWS STORM PREDICTION CENTER HAS ISSUED A** **SEVERE THUNDERSTORM WATCH FOR PORTIONS OF** **EASTERN IOWA** NORTHERN ILLINOIS AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-42 ### Page 214 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) **NORTHWEST INDIANA** **LAKE MICHIGAN** **EFFECTIVE THIS FRIDAY AFTERNOON FROM 1210 PM UNTIL 500 PM CDT.** HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS. THE SEVERE THUNDERSTORM WATCH AREA IS ALONG AND 75 STATUTE MILES EITHER SIDE OF A LINE FROM 40 MILES SOUTHEAST OF SOUTH BEND INDIANA TO 35 MILES SOUTHWEST OF CEDAR RAPIDS IOWA. REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. **PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING** WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY DO PRODUCE TORNADOES. **OTHER WATCH INFORMATION...CONTINUE...WW 646...** DISCUSSION...THUNDERSTORMS WILL CONTINUE TO INCREASE ACROSS WATCH AREA WHERE AIR MASS HAS BECOME STRONGLY UNSTABLE AND UNCAPPED. **VEERING SHEAR PROFILE SUPPORT STORMS EVOLVING INTO SHORT LINE** **SEGMENTS ENHANCING WIND DAMAGE POTENTIAL** AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM MOTION VECTOR 33025. ...HALES 6.4.4 Public Tornado Watch Notification Message SPC issues a Public Tornado Watch Notification Message when forecasting three or more tornadoes or any tornado which could produce F2 or greater damage. The forecast event minimum thresholds are at least 2 hours over an area at least 8,000 square miles. Below these thresholds, SPC, in collaboration with affected NWS offices, may issue convective watches along coastlines, near the Canadian and Mexican borders and for any ongoing organized severe convection. A Public Tornado Watch Notification Message contains the area description and axis, watch expiration time, the term “damaging tornadoes”, a description of the largest hail size and strongest thunderstorm wind gusts expected, the definition of the watch, a call to action statement, a list of other valid watches, a brief discussion of meteorological reasoning, and technical information for the aviation community. SPC includes the term “adjacent coastal waters” when the watch affects coastal waters adjacent to the Pacific/Atlantic coast, Gulf of Mexico, or Great Lakes. Adjacent coastal waters refers to a WFO’s near shore responsibility (out to 20 nautical miles for oceans), except for convective watches which include portions of the Great Lakes. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-43 ### Page 215 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) SPC issues a watch cancellation message whenever it cancels a watch prior to the expiration time. The text of the message will specify the number and area of the cancelled watch. 6.4.4.1 Format of a Public Tornado Watch Notification Message WWUS20 KWNS ddhhmm (ICAO communication header) URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER nnnn NWS STORM PREDICTION CENTER NORMAN OK time am/pm time zone day mon dd yyyy **THE STORM PREDICTION CENTER HAS ISSUED A** **TORNADO WATCH FOR PORTIONS OF** **PORTION OF STATE** **PORTION OF STATE** **AND ADJACENT COASTAL WATERS (IF REQUIRED)** EFFECTIVE (TIME PERIOD) UNTIL hhmm am/pm time zone. ...THIS IS A PARTICULARLY DANGEROUS SITUATION (IF FORECAST)... DESTRUCTIVE TORNADOES...HAIL TO X INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO XX MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS. **NARRATIVE DESCRIPTION OF WATCH AREA USING A LINE AND ANCHOR POINTS.** **DISTANCES TO EITHER SIDE OF THE LINE WILL BE IN STATUTE MILES.** **CALL TO ACTION STATEMENTS** OTHER WATCH INFORMATION...OTHER WATCHES IN EFFECT AND IF THIS WATCH REPLACES A PREVIOUS WATCH. **NARRATIVE DISCUSSION OF REASON FOR THE WATCH.** **AVIATION...BRIEF DESCRIPTION OF SEVERE WEATHER THREAT TO AVIATORS.** HAIL SIZE WILL BE GIVEN IN INCHES AND WIND GUSTS IN KNOTS. MAXIMUM STORM TOPS AND A MEAN STORM VECTOR WILL ALSO BE GIVEN. $$ ..FORECASTER NAME.. MM/DD/YY 6.4.4.2 Example of a Public Tornado Watch Notification Message WWUS20 KWNS 050550 (ICAO communication header) **URGENT - IMMEDIATE BROADCAST REQUESTED TORNADO WATCH NUMBER 243** NWS STORM PREDICTION CENTER NORMAN OK AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-44 ### Page 216 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 1250 AM CDT MON MAY 5 2003 **THE NWS STORM PREDICTION CENTER HAS ISSUED A** **TORNADO WATCH FOR PORTIONS OF** **WESTERN AND CENTRAL ARKANSAS** **SOUTHERN MISSOURI** **FAR EASTERN OKLAHOMA** **EFFECTIVE THIS MONDAY MORNING FROM 1250 AM UNTIL 600 AM CDT.** ...THIS IS A PARTICULARLY DANGEROUS SITUATION... **DESTRUCTIVE TORNADOES...LARGE HAIL TO 2 INCHES IN DIAMETER...** **THUNDERSTORM WIND GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.** THE TORNADO WATCH AREA IS ALONG AND 100 STATUTE MILES EAST AND WEST OF A LINE FROM 15 MILES WEST NORTHWEST OF FORT LEONARD WOOD MISSOURI TO 45 MILES SOUTHWEST OF HOT SPRINGS ARKANSAS. REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. **PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR THREATENING** **WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS AND POSSIBLE WARNINGS.** OTHER WATCH INFORMATION...THIS TORNADO WATCH REPLACES TORNADO WATCH NUMBER 237. WATCH NUMBER 237 WILL NOT BE IN EFFECT AFTER 1250 AM CDT. CONTINUE...WW 239...WW 240...WW 241...WW 242... **DISCUSSION...SRN MO SQUALL LINE EXPECTED TO CONTINUE EWD...WHERE** LONG/HOOKED HODOGRAPHS SUGGEST THREAT FOR EMBEDDED SUPERCELLS/POSSIBLE TORNADOES. FARTHER S...MORE WIDELY SCATTERED SUPERCELLS WITH A THREAT FOR TORNADOES WILL PERSIST IN VERY STRONGLY DEEP SHEARED/LCL ENVIRONMENT IN AR. AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM MOTION VECTOR 26045. . ..CORFIDI AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-45 ### Page 217 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.5 Products for Tropical Cyclones The NWS issues SIGMETs, Convective SIGMETs and CWAs to inform the aviation community about the potential or existence of tropical cyclones and the adverse conditions associated with them. These above listed products are the primary source of information. The NWS also issues other products pertaining to Tropical Cyclones. These additional products are defined in this section. 6.5.1 Aviation Tropical Cyclone Advisory (TCA) The Aviation Tropical Cyclone Advisory (TCA) is intended to provide short-term tropical cyclone forecast guidance for international aviation safety and routing purposes. It is prepared by the National Hurricane Center (NHC) and the Central Pacific Hurricane Center (CPHC) in Honolulu, Hawaii, for all on-going tropical cyclone activity in their respective areas of responsibility. This requirement is stated in the World Meteorological Organization Region IV hurricane plan. Any valid TCA in the Atlantic or eastern Pacific is available on the NHC web site at: http://www.nhc.noaa.gov. Any valid TCA for the central Pacific is available on the CPHC web site at: http://www.prh.noaa.gov/hnl/cphc/ 6.5.1.1 Issuance TCAs are issued at 0300, 0900, 1500, and 2100 UTC and are valid from the time of issuance until the next scheduled issuance or update. 6.5.1.2 Content TCAs list the current tropical cyclone position, motion and intensity, and 12-, 18- and 24-hour forecast positions and intensities. It is an alphanumeric text product produced by hurricane forecasters and consists of information extracted from the official forecasts. This forecast is produced from subjective evaluation of current meteorological and oceanographic data as well as output from numerical weather prediction models, and is coordinated with affected NWS offices, the NWS National Centers, and the Department of Defense. 6.5.1.3 Format The format of the Aviation Tropical Cyclone Advisory is as follows: FKaa2i cccc ddhhmm (ICAO communication header) (TROPICAL CYCLONE TYPE) (NAME)ICAO ADVISORY NUMBER ## (ISSUING OFFICE CITY STATE) BBCCYYYY time UTC day of week mon dd yyyy TEXT $$ NOTE: As part of the header, a coded string is appended at the end of the “ISSUING OFFICE CITY STATE” line. (Example: NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL **BBCCYYY)** Where: (BB) is the basin AL – North Atlantic, EP – East Pacific, or CP – Central Pacific Where: (CC) is the cyclone number (01, 02, 03,…49) Where: (YYYY) is the 4 digit year. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-46 ### Page 218 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 6.5.1.4 Aviation Tropical Cyclone Advisory (TCA) Example **FKNT25 KNHC 210900 TCANT5** TROPICAL STORM ICAO ADVISORY NUMBER 27 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092007 0900 UTC SUN OCT 21 2007 TC ADVISORY DTG: 20071021/0900Z TCAC: KNHC TC: ERNESTO NR: 027 PSN: N3000 W08012 MOV: N 13KT C: 0998HPA MAX WIND: 045KT FCST PSN + 06 HR: 211200 N3106 W07951 FCST MAX WIND + 06 HR: 045KT FCST PSN + 12 HR: 211800 N3206 W07930 FCST MAX WIND + 12 HR: 050KT FCST PSN + 18 HR: 220000 N3321 W07903 FCST MAX WIND + 18 HR: 045KT FCST PSN + 24 HR: 220600 N3436 W07836 FCST MAX WIND + 24 HR: 040KT NXT MSG: 20071021/1500Z $$ 6.5.2 Tropical Cyclone Public Advisory (TCP) A Tropical Cyclone Public Advisory (TCP) is the primary tropical cyclone information product issued to the public. The TCP provides critical tropical cyclone watch, warning, and forecast information for the protection of life and property. 6.5.2.1 TCP Responsibility The National Hurricane Center (NHC), as a part of the Tropical Prediction Center (TPC); the Central Pacific Hurricane Center (CPHC); and Weather Forecast Office (WFO) Tiyan, Guam, issue TCPs. In the Atlantic and central Pacific, NHC and CPHC issue TCPs for all tropical cyclones respectively. In the eastern Pacific, NHC will issue public advisories when watches or warnings are required, or the tropical cyclone is otherwise expected to impact nearby land areas. In the western Pacific, WFO Guam will issue public advisories generally based on the tropical cyclone bulletins of the Joint Typhoon Warning Center (JTWC) for all tropical cyclones expected to affect land within 48 hours. Valid TCP in the Atlantic or eastern Pacific is available on the NHC web site at: http://www.nhc.noaa.gov. Valid TCP for the central Pacific is available on the CPHC web site at: http://www.prh.noaa.gov/hnl/cphc/. AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-47 ### Page 219 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) TCPs issued by WFO Guam for the western Pacific are available at: http://www.prh.noaa.gov/pr/guam/cyclone.php. 6.5.2.2 TCP Issuance The initial advisory may be issued when data confirm a tropical cyclone has developed. The title of the advisory will depend upon the intensity of the tropical cyclone as listed below. • A tropical depression advisory refers to a tropical cyclone with 1-minute sustained winds up to 33 knots (38 mph). • A tropical storm advisory will refer to tropical cyclones with 1-minute sustained surface winds 34 to 63 knots (39 to 73 mph). • A hurricane/typhoon advisory will refer to tropical cyclones with winds 64 knots (74 mph) or greater. Public advisories are discontinued when the tropical cyclone: • Ceases to be a tropical cyclone; that is, it becomes extratropical, a remnant low, or dissipates, or • Is centered over land, is below tropical storm strength, and is not forecast to move back over water as a tropical cyclone, and no coastal tropical cyclone watches or warnings are in effect. • For Guam when the tropical cyclone moves out of the WFO area of responsibility. Tropical Cyclone Public Advisories are issued according to the schedule below and are valid from the time of issuance until the next scheduled issuance or update. Valid position times correspond to the advisory time. Table 6-10. Tropical Cyclone Public Advisory Issuance Schedule **TPC/CPHC** **ISSUANCE TIME (UTC)** **WFO GUAM** **ISSUANCE TIME (UTC) 0300 0400 0900 1000 1500 1600 2100 2200** Times in advisories are local time of the affected area; however, local time and UTC are used when noting the storm’s location. All advisories use statute miles and statute miles per hour. The Tropical Cyclone Center (TPC and CPHC) and WFO Guam, at their discretion, may use nautical miles/knots in parentheses immediately following statute miles/mph. Advisories include the metric units of kilometers and kilometers per hour following the equivalent English units except when the United States is the only country threatened. NHC, CPHC and WFO Guam issue tropical storm/hurricane/typhoon watches if tropical storm/hurricane/typhoon conditions are possible over land areas within 36 hours, except 48 AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-48 ### Page 220 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) hours in the western north Pacific. Tropical storm watches are not issued if the tropical cyclone is forecast to reach hurricane/typhoon intensity within the watch period. Tropical storm/hurricane/typhoon warnings are issued when tropical storm/hurricane/typhoon conditions along the coast are expected within 24 hours. Tropical storm warnings are issued at the discretion of the hurricane specialist when gale warnings, not related to the pending tropical storm, are already in place. Tropical storm warnings may be issued on either side of a hurricane/typhoon warning area. 6.5.2.2.1 TCP Intermediate Issuances Intermediate Public Advisories are issued on a 2- to 3-hourly interval between scheduled advisories (see times of issuance below). 3-hourly intermediate advisories are issued whenever a tropical storm or hurricane watch/warning is in effect. 2-hourly intermediates are issued whenever tropical storm or hurricane warnings are in effect and coastal radars are able to provide responsible Tropical Cyclone Centers with a reliable hourly center position. For clarity, when intermediate public advisories are issued, a statement is included at the end of the scheduled public advisory informing users when an intermediate advisory may be issued, i.e., “AN INTERMEDIATE ADVISORY WILL BE ISSUED BY THE CENTRAL PACIFIC HURRICANE CENTER AT 2 PM HST FOLLOWED BY THE NEXT COMPLETE ADVISORY ISSUANCE AT 5 PM HST.” Table 6-11. Intermediate Tropical Cyclone Public Advisory Issuance Schedule **TPC/CPHC** **ISSUANCE TIME (UTC)** **WFO GUAM** ISSUANCE TIME (UTC) 3-Hourly Issuances 0000 0100 0600 0700 1200 1300 1800 1900 2-Hourly Issuances 2300 0000 0100 0200 0500 0600 0700 0800 1100 1200 1300 1400 1700 1800 1900 2000 Intermediate advisories are not used to issue tropical cyclone watches or warnings. They can be used to clear all, or parts of, a watch or warning area. Content is similar to the scheduled advisory. 6.5.2.3 TCP Content Advisories list all tropical cyclone watches and warnings in effect. The first advisory in which watches or warnings are mentioned will give the effective time of the watch or warning, except when it is being issued by other countries and the time is not known. Except for tropical storms and hurricanes/typhoons forming close to land, a watch will precede a warning. Once a watch is in effect, it will either be replaced by a warning or remain in effect until the threat of the tropical AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-49 ### Page 221 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) cyclone conditions has passed. A hurricane/typhoon watch and a tropical storm warning can be in effect for the same section of coast at the same time. All advisories include the location of the center of the tropical cyclone by its latitude and longitude, and distance and direction from a well known point, preferably downstream from the tropical cyclone. If the forecaster is unsure of the exact location of a depression, the position may be given as within 50, 75, etc., miles of a map coordinate. When the center of the tropical cyclone is over land, its position is given referencing the state or country in which it is located and in respect to some well known city, if appropriate. Movement forecasts apply to the tropical cyclone's center. The present movement is given to 16 points of the compass when possible. A 24-hour forecast of movement in terms of a continuance or departure from the present movement and speed is also included. This can be reduced to a 12-hour forecast. Uncertainties in either the tropical cyclone's location or movement will be explained in the advisory. An outlook beyond 24 hours (out to 72 hours when appropriate) may be included in the text of the advisory. Maximum observed 1-minute sustained surface wind speed rounded to the nearest 5 mph is given. During landfall threats, specific gust values and phrases like “briefly higher in squalls” may be used. The area (or radius) of both tropical and hurricane/typhoon force winds is given. The storm may also be compared to some memorable hurricane or referred to by relative intensity. Where appropriate, the Saffir/Simpson Hurricane Scale (SSHS) is used in public releases. Central pressure values in millibars and inches are provided as determined by available data. The inland impacts of tropical cyclones will be highlighted in advisories. This includes the threat of strong winds, heavy rainfall, flooding, and tornadoes. The extent and magnitude of the inland winds is included as well as anticipated rainfall amounts and the potential for flooding and tornadoes. Tornado and flood watches will be mentioned as appropriate. 6.5.2.4 TCP Format The format of the Tropical Cyclone Public Advisory is as follows: WTaaii cccc ddhhmm TCPxxx **BULLETIN (TROPICAL CYCLONE TYPE) (NAME) ADVISORY NUMBER XX.** (ISSUING OFFICE CITY STATE) BBCCYYYY time am/pm time zone day month dd YYYY ...HEADLINE... TEXT $$ **FORECASTER NAME** NOTE: As part of the header, a coded string is appended at the end of the “ISSUING OFFICE CITY STATE” line (Example: NWS TPC/NATIONAL HURRICANE CENTER AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-50 ### Page 222 Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) **MIAMI FL BBCCYYYY)** Format: where: (BB) is the basin AL - North Atlantic, EP - East Pacific, CP - Central Pacific WP – western Pacific where: (CC) is the cyclone number (01, 02, 03,...49) where: (YYYY) is the 4 digit year. 6.5.2.5 Tropical Storm Public Advisory (TCP) Example **WTNT34 KNHC 260359 MIATCPAT4** BULLETIN TROPICAL STORM DEBBY ADVISORY NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL042006 1100 PM AST FRI AUG 25 2006 ...DEBBY BARELY HANGING ON AS A TROPICAL STORM... AT 1100 PM AST...0300Z...THE CENTER OF TROPICAL STORM DEBBY WAS LOCATED NEAR LATITUDE 25.2 NORTH...LONGITUDE 45.6 WEST OR ABOUT 1400 MILES...2255 KM...SOUTHWEST OF THE AZORES. **DEBBY IS MOVING TOWARD THE WEST-NORTHWEST NEAR 14 MPH...22 KM/HR...** **AND A TURN TO THE NORTHWEST AND THEN NORTH-NORTHWEST IS EXPECTED OVER THE NEXT 24 HOURS.** MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/HR...WITH HIGHER GUSTS. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 24 HOURS. **TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 105 MILES...165 KM FROM THE CENTER.** **ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB...29.77 INCHES.** REPEATING THE 1100 PM AST POSITION...25.2 N...45.6 W. MOVEMENT TOWARD...WEST-NORTHWEST NEAR 14 MPH. MAXIMUM SUSTAINED WINDS...40 MPH. MINIMUM CENTRAL PRESSURE...1008 MB. **THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT 500 AM AST.** $$ **FORECASTER KNABB** 6.5.2.6 Hurricane/Typhoon Public Advisory Example **WTNT32 KNHC 282058 TCPAT2** AC 00-45F, CHG 2 Section 6: Products for Aviation Hazards Page 6-51 The text continues at https://openairdocs.org/ac/00-45F-CHG-2.md?from=223 --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.