11/14/16 Aviation Weather Services AC 00-45H 5-13 Table 5-3. Decoding a SIGMET Outside of the Continental U.S.
Line 1 Content WSPA07 Description 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 Issuance office PHFO 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 5-7, SIGMET Outside the Continental U.S. Decoding Example, 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.
(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.
5.1.5.4 SIGMETs for Volcanic Ash—Outside the CONUS.
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
11/14/16 Aviation Weather Services AC 00-45H 5-14 (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 AOR.
SIGMETs for volcanic ash cloud are valid up to 6 hours and provide an observed or forecast location of the ash cloud at the beginning of the SIGMET. A 6-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 6 hours while the volcanic ash cloud hazard exists or is expected to exist.
5.1.5.5 SIGMETs for Tropical Cyclone—Outside the CONUS.
SIGMETs 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 kts independent of the wind averaging time used by the Tropical Cyclone Advisory Center (TCAC).
SIGMETs for tropical cyclones will be valid up to 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 6 hours while the tropical cyclone wind remains or are expected to remain above 34 kts.
5.1.5.6 SIGMET Cancellation—Outside the CONUS.
SIGMETs are canceled when the phenomena is no longer occurring or expected to occur in the AOR.
5.1.5.7 SIGMET Amendments—Outside the 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).
5.1.5.8 SIGMET Corrections—Outside the 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.
11/14/16 Aviation Weather Services AC 00-45H 5-15
5.1.5.9 SIGMET for Volcanic Ash Example—Outside the CONUS.
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 WI N1730 W06400 - N1700 W06300 - N1650 W06300 - N1710 W06400 - N1730 W06400. SFC/060.
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 (KKCI) 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 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. From the surface to 6,000 feet MSL. 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/10minutes north, 65 degrees/00 minutes west to 17 degrees/30 minutes north, 65 degrees/ 00 minutes west.
11/14/16 Aviation Weather Services AC 00-45H 5-16
5.1.5.10 SIGMET for Tropical Cyclone Example—Outside the CONUS.
WSNT03 KKCI 081451 SIGA0C 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 (KKCI) 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.
5.2 Airmen’s Meteorological Information (AIRMET).
An AIRMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena that may affect the safety of aircraft operations, but at intensities lower than those that 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 give notice to operators and aircrews of potentially hazardous en route conditions.
Although the areas where the AIRMETs apply may be shown graphically, a graphical depiction of the AIRMET area is not the entire AIRMET. Additional information regarding the AIRMET may be contained in the text version.
• AIRMETs are available for the CONUS on http://www.aviationweather.gov.
• AIRMETs are available for Alaska on the AAWU Web site.
• AIRMETs are available for Hawaii on the NWS WFO Honolulu Web site.
11/14/16 Aviation Weather Services AC 00-45H 5-17
5.2.1 AIRMET Issuance.
AIRMETs are issued from the three MWOs located at the AWC, AAWU, and WFO Honolulu. Their AORs are:
• AWC: The CONUS and adjacent coastal waters (see Figure 5-8, AWC AIRMET Areas of Responsibility—Continental U.S.).
• AAWU: Alaska and adjacent coastal waters (see Figure 5-9, AAWU Flight Advisory and Area Forecast (FA) Zones—Alaska).
• WFO Honolulu: Hawaii and adjacent waters (see Figure 5-10, WFO Honolulu AIRMET Areas of Responsibility—Hawaii).
Figure 5-8. AWC AIRMET Areas of Responsibility—Continental U.S.
Figure 5-9. AAWU Flight Advisory and Area Forecast (FA) Zones—Alaska
11/14/16 Aviation Weather Services AC 00-45H 5-18 Table 5-4. AAWU Flight Advisory and Area Forecast (FA) 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 Figure 5-10. WFO Honolulu AIRMET Areas of Responsibility—Hawaii
11/14/16 Aviation Weather Services AC 00-45H 5-19
5.2.2 AIRMET Issuance Criteria.
An AIRMET may be issued when any of the following weather phenomena are occurring or are expected to occur over an area of at least 3,000 mi2:
• Ceiling less than 1,000 ft and/or visibility less than 3 sm (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 obscuration are included, but not 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 kts (STG SFC WND).
• Moderate icing (MOD ICE).
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 ft MSL (or SFC as appropriate) are specified.
• Non-Convective low-level wind shear potential below 2,000 ft AGL (LLWS POTENTIAL).
5.2.3 AIRMET Standardization.
All AIRMETs follow these standards:
• All heights or altitudes are referenced to above MSL, 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 ft, the level is preceded by FL to represent flight levels
(e.g., FL180).
• Messages are prepared in abbreviated plain language using contractions from the current edition of Order 7340.2. 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 (Aviation Routine Weather Report (METAR)/Special Weather Report (SPECI)). See the Federal Meteorological
11/14/16 Aviation Weather Services AC 00-45H 5-20 Handbook (FMH) No. 1, Surface Weather Observations and Reports, or paragraph 3.1 of this document.
Note: See Appendix A for definitions of common terms used in AIRMETs.
5.2.4 AIRMET Bulletins, Issuance Times, and Valid Period.
AIRMETs are issued as bulletins containing one or more AIRMET messages following the schedule listed in Table 5-5, AIRMET Issuance Schedule. AIRMETs are issued 4 times a day except for those in Alaska, which are issued three times a day. Unscheduled AIRMETs are issued when conditions are occurring or expected to occur but were not forecast.
Table 5-5. 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 0415 (DT)/ 0515 (ST) 1215 (DT)/ 1315 (ST) 2015 (DT)/ 2115 (ST) None Hawaii 0400 1000 1600 2200 Note: DT—During Alaska Daylight Time, ST—During Alaska Standard Time AIRMETs are valid for 6 hours except for those in Alaska, which are valid for 8 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 6 hours following the AIRMET ending time. Also, AIRMET bulletins can contain a separate outlook when conditions meeting AIRMET criteria are expected to occur during the 6-hour (8-hour for Alaska) period after the valid time of the AIRMET bulletin.
5.2.5 AIRMET Format and Example.
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 1 after 0000 UTC each day.)
11/14/16 Aviation Weather Services AC 00-45H 5-21 o AIRMET Sierra describes IFR (instrument flight rules) conditions and/or extensive mountain obscurations. Hawaii AIRMETs for mountain obscuration may be issued for an area less than 3,000 mi2.
o AIRMET Tango describes moderate turbulence, sustained surface winds of 30 kts 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.
• 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 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 (FA) zone when conditions are expected to occur during the 8-hour period after the valid time of the AIRMET bulletin.
Figure 5-11. AIRMET Bulletin Decoding—Example
11/14/16 Aviation Weather Services AC 00-45H 5-22 Table 5-6. 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 3A AIRMET IFR..ME NH VT MA CT RI NY NJ AND CSTL WTRS Product type/series… Phenomenon location (states) 3B AIRMET MTN OBSCN..ME NH VT MA NY PA 4A FROM CAR TO YSJ TO 150E ACK TO EWR TO YOW TO CAR Phenomenon location (VOR locations) 4B FROM CAR TO MLT TO CON TO SLT TO SYR TO CAR 5A CIG BLW 010/VIS BLW 3SM PCPN/BR. CONDS CONT BYD 02Z THRU 08Z. Phenomenon description 5B MTNS OBSCD BY CLDS/PCPN/BR. CONDS CONT BYD 02Z THRU 08Z.
The AIRMET bulletin in Figure 5-6 is decoded as follows:
(Line 1) AIRMET SIERRA issued for the Boston area at 1945Z on the 21st day of the month. “SIERRA” contains information on Instrument Flight Rules (IFR) and/or mountain obscurations.
(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.
11/14/16 Aviation Weather Services AC 00-45H 5-23 (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.
5.2.5.1 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.
5.2.5.2 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.
5.3 Graphical Airman’s Meteorological Advisory (G-AIRMET).
The Graphical AIRMET (G-AIRMET) product is a decision-making tool based on weather “snapshots” displayed at short time intervals. The G-AIRMET identifies hazardous weather in space and time more precisely than text products, enabling pilots to maintain high safety margins while flying more efficient routes.
The NWS’s goal is to maximize aviation safety and air space efficiency by providing the most accurate and timely weather information possible to enhance both pre-flight and in-flight decision making. For decades, NWS has issued text-based AIRMETs that have provided broad-scale descriptions of hazardous weather. Often referred to as a time “smear,” the text-based AIRMET requires meteorologists to describe hazardous weather over large geographical areas for 6-hour periods. G-AIRMET provides more precise and informative weather hazard depictions than the text-only AIRMET.
Aviation weather users have found that pictures are worth a thousand contractions.
G-AIRMETs provide a better path from the aviation meteorologist to the weather user, by providing precise, interactive, and easy-to-understand graphical displays. Meteorologists can put their energy into creating and updating G-AIRMET weather graphics. The traditional text AIRMET coincides with G-AIRMET information because texts AIRMETs are formatted from G-AIRMET information.
G-AIRMETs are available for the CONUS and adjacent coastal waters only and can be viewed on http://www.aviationweather.gov.
11/14/16 Aviation Weather Services AC 00-45H 5-24
5.3.1 G-AIRMET Issuance.
G-AIRMETs are issued by the AWC every 6 hours and are updated/amended as necessary, coinciding with the text AIRMET products.
Table 5-7. G-AIRMET Issuance Schedule 1st Scheduled Issuance (UTC) 2nd Scheduled Issuance (UTC) 3rd Scheduled Issuance (UTC) 4th Scheduled Issuance (UTC) CONUS 0300 0900 1500 2100
5.3.2 G-AIRMET Content.
G-AIRMET snapshots are graphical forecasts of en route weather hazards valid at discrete times no more than 3 hours apart for a period of up to 12 hours into the future (00, 03, 06, 09, and 12 hours). 00 hour represents the initial conditions, and the subsequent 3-hourly graphics depict the area affected by the particular hazard at that valid time.
The AWC’s Web site provides several options to display the G-AIRMET. There is an interactive display as well as snapshots that may be viewed as static (single), combined, and looped images using the tools provided on the Web page. The following are examples of G-AIRMET snapshot static images.
G-AIRMET depicts the following en route aviation weather hazards:
• IFR Ceiling and Visibility (see Figure 5-12, G-AIRMET—Ceiling and Visibility (IFR) Snapshot Example).
o Areas of cloud ceilings with bases less than 1000 ft AGL and/or areas of surface visibilities below 3 sm, including the weather causing the visibility restriction. The cause of the visibility restriction includes only PCPN, FU, HZ, BR, FG, and BLSN.