AC 00-45E

AVIATION

WEATHER

SERVICES AC 00-45E U.S. DEPARTMENT OF COMMERCE

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

NATIONAL WEATHER SERVICE

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL AVIATION ADMINISTRATION Revised December 1999

i

FOREWORD AC 00-45E, Aviation Weather Services, is published jointly by the Federal Aviation Administration and the National Weather Service (NWS). This document supplements the companion manual AC 00-6A, Aviation Weather, that deals with weather theories and hazards.

This advisory circular, AC 00-45E, explains weather service in general and the details of interpreting and using coded weather reports, forecasts, and observed and prognostic weather charts. Many charts and tables apply directly to flight planning and inflight decisions. It can also be used as a source of study for pilot certification examinations.

The AC 00-45E was written primarily by Kathleen Schlachter with contributions from Jon Osterberg, Doug Streu, and Robert Prentice. A special thanks to Sue Roe for her help and patience in editing this manual.

Comments and suggestions for improving this publication are encouraged and should be directed to:

National Weather Service Coordinator, W/SR64 Federal Aviation Administration Mike Monroney Aeronautical Center P.O. Box 25082 Oklahoma City, OK 73125-0082 Advisory Circular AC 00-45E supersedes AC 00-45D, Aviation Weather Services, revised 1995.

iii

TABLE OF CONTENTS Section 1 - THE AVIATION WEATHER SERVICE PROGRAM

National Oceanic and Atmospheric Administration (NOAA)1-1

Federal Aviation Administration (FAA)1-3

Observations1-8

Communications Systems1-10

Users1-10

Section 2 - AVIATION ROUTINE WEATHER REPORT (METAR)

Type of Report2-1

ICAO Station Identifier2-2

Date and Time of Report2-3

Modifier (As Required)2-3

Wind2-4

Visibility2-5

Runway Visual Range (RVR) (As Required)2-6

Weather Phenomena2-6

Sky Condition2-10

Temperature/Dew Point Group2-19

Altimeter2-19

Remarks (RMK) (As Required)2-20

Section 3 - PILOT AND RADAR REPORTS, SATELLITE PICTURES,AND RADIOSONDE ADDITIONAL DATA (RADATs)

Pilot Weather Reports (PIREPs)3-1

Radar Weather Reports (SDs)3-6

Satellite Weather Pictures3-11

Radiosonde Additional Data (RADATs)3-15

Section 4 - AVIATION WEATHER FORECASTS

Aviation Terminal Forecast (TAF)4-1

Aviation Area Forecast (FA)4-17

Inflight Aviation Weather Advisories4-23

Alaska, Gulf of Mexico, and International Area Forecasts (FAs)4-27

Transcribed Weather Broadcast (TWEB) Text Products4-31

Winds and Temperatures Aloft Forecast (FD)4-35

Center Weather Service Unit (CWSU) Products4-38

Hurricane Advisory (WH)4-40

Convective Outlook (AC)4-41

Severe Weather Watch Bulletins (WWs) and Alert Messages (AWWs)4-42

iv Section 5 - SURFACE ANALYSIS CHART

Valid Time5-1

Isobars5-1

Pressure Systems5-1

Fronts5-1

Troughs and Ridges5-1

Other Information5-2

Using the Chart5-2

Section 6 - WEATHER DEPICTION CHART

Plotted Data6-1

Analysis6-4

Using the Chart6-4

Section 7 - RADAR SUMMARY CHART

Echo (Precipitation) Type7-1

Intensity7-2

Echo Configuration and Coverage7-2

Echo Tops7-3

Echo Movement7-3

Severe Weather Watch Areas7-3

Using the Chart7-3

Section 8 - CONSTANT PRESSURE ANALYSIS CHARTS

Plotted Data8-1

Analysis8-1

Three-Dimensional Aspects8-3

Using the Charts8-3

Section 9 - COMPOSITE MOISTURE STABILITY CHART

Stability Panel9-1

Precipitable Water Panel9-4

Freezing Level Panel9-5

Average Relative Humidity Panel9-9

Using the Chart9-10

v Section 10 - WINDS AND TEMPERATURES ALOFT CHART

Forecast Winds and Temperatures Aloft (FD)10-1

Observed Winds Aloft10-3

Using the Charts10-3

International Flights10-4

SECTION 11 - SIGNIFICANT WEATHER PROGNOSTIC CHARTS

U.S. Low-Level Significant Weather (Sig Wx) Prog11-1

36- and 48-Hour Surface Prog11-5

High-Level Significant Weather Prog11-6

Section 12 - CONVECTIVE OUTLOOK CHART

Day 1 Convective Outlook12-1

Day 2 Convective Outlook12-1

Levels of Risk12-1

Using the Chart12-2

Section 13 – VOLCANIC ASH ADVISORY CENTER PRODUCTS

Volcanic Ash Advisory Statement (VAAS)13-1

Volcanic Ash Forecast Transport And Dispersion Chart (VAFTAD)13-2

VAFTAD Product13-3

Using the Chart13-3

Section 14 - TURBULENCE LOCATIONS, CONVERSION AND DENSITY

ALTITUDE TABLES, CONTRACTIONS AND ACRONYMS,

SCHEDULE OF PRODUCTS, NATIONAL WEATHER SERVICE STATION IDENTIFIERS, WSR-88D SITES, AND INTERNET

ADDRESSES

Locations of Probable Turbulence14-1

Standard Conversion Table14-3

Density Altitude14-4

Contractions and Acronyms14-6

Scheduled Issuance and Valid Times of Forecast Products14-20

National Weather Service Station Identifiers14-21

WSR-88D Sites14-23

Internet Addresses14-25

December 1999 1-1 Section 1

THE AVIATION WEATHER SERVICE PROGRAM Providing weather service to aviation 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 and communication services to the aviation community.

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (NOAA) The National Oceanic and Atmospheric Administration (NOAA) is an agency of the Department of Commerce. NOAA is one of the leading scientific agencies in the U.S. Government. Among its six major divisions are the National Environmental Satellite Data and Information Service (NESDIS) and the NWS.

NATIONAL ENVIRONMENTAL SATELLITE DATA AND INFORMATION SERVICE (NESDIS) The National Environmental Satellite Data and Information Service (NESDIS) is located in Washington, D.C., and directs the weather satellite program. Figures 3-2 and 3-3 are examples of Geostationary Operational Environmental Satellite (GOES) images. These images are available to NWS meteorologists and a wide range of other users for operational use.

Satellite Analysis Branch (SAB) The Satellite Analysis Branch (SAB) coordinates the satellite and other known information for the NOAA Volcanic Hazards Alert program under an agreement with the FAA. SAB works with the NWS as part of the Washington D.C. Volcanic Ash Advisory Center (VAAC).

NATIONAL WEATHER SERVICE (NWS) The National Weather Service (NWS) collects and analyzes meteorological and hydrological data and subsequently prepares forecasts on a national, hemispheric, and global scale. The following is a description of the NWS facilities tasked with these duties.

National Centers for Environmental Prediction (NCEP) There are nine separate national centers under National Centers for Environmental Prediction (NCEP), each with its own specific mission. They are the Climate Prediction Center, Space Environment Center, Marine Prediction Center, Hydrometeorological Prediction Center, Environmental Modeling Center, NCEP Center Operations, Storm Prediction Center, Aviation Weather Center, and the Tropical Prediction Center.

National Center Operations (NCO) Located in Washington, D.C., the National Center Operations (NCO) is the focal point of the NWS’s weather processing system. From worldwide weather reports, NCO prepares automated weather analysis charts and guidance forecasts for use by NWS offices and other users.

December 1999 1-2 Some NCO products are specifically prepared for aviation, such as the winds and temperatures aloft forecast. Figure 4-9 is the network of forecast winds and temperatures aloft for the contiguous 48 states.

Figure 4-10 shows the Alaskan and Hawaiian network.

NCO is part of VAAC, which runs an ash dispersion model. NCO works with SAB to fulfill the VAAC responsibilities to the aviation communities regarding potential volcanic ash hazards to aviation.

Storm Prediction Center (SPC) The Storm Prediction Center (SPC) is charged with monitoring and forecasting severe weather over the 48 continental United States. Its products include convective outlooks and forecasts, as well as severe weather watches. The center also develops severe weather forecasting techniques and conducts research.

The SPC is located in Norman, Oklahoma, near the heart of the area most frequently affected by severe thunderstorms.

Hydrometeorological Prediction Center (HPC) The Hydrometeorological Prediction Center (HPC) prepares weather charts which include basic weather elements of temperature, fronts and pressure patterns.

Aviation Weather Center (AWC) The Aviation Weather Center (AWC), located in Kansas City, Missouri, issues warnings, forecasts, and analyses of hazardous weather for aviation interests. The center identifies existing or imminent weather hazards to aircraft in flight and creates warnings for transmission to the aviation community. It also produces operational forecasts of weather conditions expected during the next 2 days that will affect domestic and international aviation interests. As a Meteorological Watch Office (MWO) under regulations of the International Civil Aviation Organization (ICAO), meteorologists in this unit prepare and issue aviation area forecasts (FAs) and inflight weather advisories (Airman’s Meteorological Information [AIRMET], Significant Meteorological Information [SIGMET], and Convective SIGMETs) for the contiguous 48 states.

Tropical Prediction Center (TPC) The Tropical Prediction Center (TPC) is located in Miami, Florida. The National Hurricane Center, as an integral part of TPC, issues hurricane advisories for the Atlantic, the Caribbean, the Gulf of Mexico, the eastern Pacific, and adjacent land areas. The center also develops hurricane forecasting techniques and conducts hurricane research. The Central Pacific Hurricane Center in Honolulu, Hawaii, issues advisories for the central Pacific Ocean.

TPC prepares and distributes tropical weather, aviation and marine analyses, forecasts, and warnings. As an MWO, TPC meteorologists prepare and issue aviation forecasts, SIGMETs, and Convective SIGMETs for their tropical Flight Information Region (FIR).

Weather Forecast Office (WFO) A Weather Forecast Office (WFO) issues various public and aviation forecast and weather warnings for its area of responsibility. In support of aviation, WFOs issue terminal aviation forecasts (TAFs) and transcribed weather broadcasts (TWEBs). As MWOs, the Guam and Honolulu Hawaii WFOs issue aviation area forecasts and inflight advisories (AIRMETs, and international SIGMETs). Figures 4-1 through 4-4 show locations for which TAFs are issued. Figure 4-8 shows the TWEB routes.

December 1999 1-3 Alaskan Aviation Weather Advisory Unit (AAWU) The Alaskan Aviation Weather Unit (AAWU) is a regional aviation forecast unit located in Anchorage, Alaska. As an MWO, AAWU meteorologists prepare and issue International SIGMETs within the Alaskan FIR, as well as domestic FAs and AIRMETs for Alaska and the adjacent coastal waters. The AAWU prepares and disseminates to the FAA and the Internet a suite of graphic products, including a graphic FA and a 24- and 36-hour forecast of significant weather. The AAWU is one of nine VAACs worldwide, preparing Volcanic Ash Advisory Statements (VAAS) for the Anchorage FIR.

FEDERAL AVIATION ADMINISTRATION (FAA) The Federal Aviation Administration (FAA) is a part of the Department of Transportation. 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.

FLIGHT SERVICE STATIONS (FSSs) The FAA is in the process of modernizing its Flight Service Station (FSS) program. The older, manual (or nonautomated) FSS is being consolidated into the newer, automated FSS (AFSS). With about one per state and with lines of communications radiating out from it, these new AFSSs are referred to as “hub” facilities. Pilot services provided previously by the older FSSs have been consolidated into facilities with new technology to improve pilot weather briefing services.

The FSS or AFSS provides more aviation weather briefing service than any other U.S Government service outlet. The FSS or AFSS provides preflight and inflight briefings, transcribed weather briefings, scheduled and unscheduled weather broadcasts, and furnishes weather support to flights in its area.

As a starting point for a preflight weather briefing, a pilot may wish to listen to one of the recorded weather briefings provided by an FSS or AFSS. For a more detailed briefing, pilots can contact the FSS or AFSS directly.

Transcribed Weather Broadcast (TWEB) The transcribed weather broadcast (TWEB) provides continuous aeronautical and meteorological information on low/medium frequency (L/MF) and very high frequency (VHF) omni-directional radio range (VOR) facilities.

At TWEB equipment locations controlling two or more VORs, the one used least for ground-to-air communications, preferably the nearest VOR, may be used as a TWEB outlet simultaneously with the nondirectional radio beacon (NDB) facility.

December 1999 1-4 The sequence, source, and content of transcribed broadcast material shall be:

1. Introduction.

2. Synopsis. Prepared by selected WFOs and stored in Weather Message Switching Center (WMSC).

3. Adverse Conditions. Extracted from inflight weather advisories, center weather advisories (CWAs), and alert severe weather watch bulletins (AWWs).

4. TWEB Route Forecasts. Includes the valid time of forecasts prepared by WFOs and stored in the WMSC.

5. Winds Aloft Forecast. Broadcast for the location nearest to the TWEB. The broadcast should include the levels for 3,000 to 12,000 feet, but shall always include at least two forecast levels above the surface.

6. Radar Reports. Local or pertinent radar weather reports (SDs) are used. If there is access to real-time weather radar equipment, the observed data is summarized using the SDs to determine precipitation type, intensity, movement, and height.

7. Surface Weather Reports (METARs). Surface/special weather reports are recorded, beginning with the local reports, then the remainder of the reports beginning with the first station east of true north and continuing clockwise around the TWEB location.

8. Density Altitude. Includes temperature and the “check density altitude” statement for any station with a field elevation at or above 2,000 feet MSL and meets a certain temperature criteria.

9. Pilot Weather Reports (PIREPs). PIREPs are summarized. If the weather conditions meet soliciting requirements, a request for PIREPs will be appended.

10. Alert Notices (ALNOT), if applicable.

11. Closing Statement.

Items 2, 3, 4, and 5 are forecasts and advisories prepared by the NWS and are discussed in detail in Section 4. The synopsis and route forecasts are prepared specifically for the TWEB by WFOs. Adverse conditions, outlooks, and winds/temperature aloft are adapted from inflight advisories, area forecasts, and the winds/temperature aloft forecasts. Radar reports and pilot reports are discussed in Section 3. Surface reports are discussed in Section 2.

December 1999 1-5 Pilots’ Automatic Telephone Weather Answering System (PATWAS) Pilots’ automatic telephone weather answering system (PATWAS) provides a continuous telephone recording of meteorological information. At PATWAS facilities where the telephone is connected to the TWEB, the information contained in the broadcast shall be in accordance with the TWEB format.

PATWAS messages are recorded and updated at a minimum of every 5 hours beginning at 0600 and ending at 2200 local time using the following procedures:

1. Introduction (describing PATWAS area).

2. Adverse Conditions. Summarized inflight weather advisories, center weather advisories, alert severe weather watch bulletins, and any other available information that may adversely affect flight in the PATWAS area.

3. VFR Flight Not Recommended Statement (VNR). When current or forecast conditions, surfacebased or aloft, would make visual flight doubtful.

4. Synopsis. Should be a reflection of current and forecast conditions using synopsis products prepared by selected WFOs or extracted from the synopsis section of the area forecast.

5. Current Conditions. Summarized current weather conditions over the broadcast area.

6. Surface Winds. Provided from local reports.

7. Forecast. Summarized forecast conditions over the PATWAS area.

8. Winds Aloft. Summarized winds aloft as forecast for the local station or as interpolated from forecasts of adjacent stations for levels 3,000 through 9,000 feet or a minimum of at least two forecast levels above the highest terrain.

9. Request for PIREPs, if applicable.

10. Alert Notices (ALNOT), if applicable.

11. Closing Announcement.

The PATWAS service holds high operational priority . This ensures the information is current and accurate. If service is reduced during the period of 2200-0600 local time, a suspension announcement is recorded including a time when the broadcast will be resumed. The Airport Facility Directory lists PATWAS telephone numbers for FSS briefing offices.

Telephone Information Briefing Service (TIBS) Telephone information briefing service (TIBS) is provided by AFSSs and provides continuous telephone recordings of meteorological and/or aeronautical information. TIBS shall contain area and/or route briefings, airspace procedures, and special announcements, if applicable.

TIBS should also contain, but not limited to, METARs, aviation terminal forecasts (TAFs), and winds/ temperatures aloft forecasts.

Each AFSS shall provide at least four route and/or area briefings. Area briefings should encompass a 50- NM radius. Each briefing should require the pilot to access no more than two channels which shall be route- and/or area-specific. Pilots shall have access to NOTAM data through an area or route briefing on a separate channel designated specifically for NOTAMs or by access to a briefer.

TIBS service is provided 24 hours a day. Recorded information shall be updated as conditions change.

Area and route forecast channels shall be updated whenever material is updated.

December 1999 1-6 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.

2. Adverse Conditions. A summary of inflight weather advisories, center weather advisories, alert severe weather watch bulletins, and any other available information that may adversely affect flight in the route/area.

3. VFR Not Recommended Statement (VNR). Included when current or forecast conditions, surface or aloft, would make the flight under visual flight rules doubtful.

4. Synopsis. A brief statement describing the type, location, and movement of weather systems and/or masses which might affect the route or the area.

5. Current Conditions. A summary of current weather conditions over the route/area.

6. Density Altitude. A “check density altitude” statement will be included for any weather reporting point with a field elevation at or above 2,000 feet MSL and meets certain temperature criteria.

7. En Route Forecast. A summary of appropriate forecast data in logical order; i.e., climb out, en route, and descent.

8. Winds Aloft. A summary of winds aloft forecast for the route/area for levels through 12,000 feet.

9. Request for PIREPs, if applicable.

10. NOTAM information that affects the route/area as stated above.

11. Military Training Activity. Included in the closing announcement.

12. ALNOT Alert Announcement. If applicable.

13. Closing Announcement. Shall be appropriate for the facility equipment and the mode of operation.

Service may be reduced during the hours of 2200 and 0600 local time. During the period of reduced service, an announcement must be recorded. The Airport Facility Directory lists TIBS telephone numbers for AFSS briefing offices. A touch-tone telephone is necessary to access the TIBS program.

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.

Hazardous Inflight Weather Advisory Service (HIWAS) The hazardous inflight weather advisory service (HIWAS) is a continuous broadcast of inflight weather advisories; i.e., SIGMETs, Convective SIGMETs, AIRMETs, AWWs, CWAs, and urgent PIREPs.

The HIWAS broadcast area is defined as the area within 150 NM of HIWAS outlets. HIWAS broadcasts shall not be interrupted/delayed except for emergency situations. The service shall be provided 24 hours a day.

An announcement shall be made if there are no hazardous weather advisories. Hazardous weather information shall be recorded if it is occurring within the HIWAS broadcast area. The broadcast shall include the following elements:

1. A statement of introduction including the appropriate area(s) and a recording time.

2. A summary of inflight weather advisories, center weather advisories, and alert severe weather watch bulletins, and any other weather 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.