• 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 mi.
• AIRMET Tango describes moderate turbulence, sustained surface winds of 30 kts or greater, and Non-Convective low-level windshear.
• 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 LINE 1 BOSS WA 211945 2 AIRMET SIERRA UPDT 3 FOR IFR AND MIN OBSCN VALID UNTIL 220200 AIRMET IFR.ME NH VT MA CT RI NY NJ AND CSTL WIRS FROM CAR TO YSJ TO 150E ACK TO EWR TO YOW TO CAR CIG BLW 010/VIS BLN 3SM PCPN/BR. CONDS CONT BYD 02Z THRU 08Z.
З AIRMET MIN OBSCN..ME NH VT MA NY PA 4 FROM CAR TO MLT TO CON TO AVP TO SYR TO CAR 5 MINS OBSCD BY CLDS/PCPN/BR. CONDS CONT BYD 02Z THRU 08Z.
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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 5-11, AIRMET Bulletin Decoding—Example, 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.
5-23 (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.
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-AIR METs are available for the CONUS and adjacent coastal waters only and can be viewed on https://www.aviationweather.gov.
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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 website 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.
Figure 5-12. G-AIRMET-Ceiling and Visibility (IFR) Snapshot Example Ceiling & Visiblity Turb High Turb Low Icing Mountain Obscuration Low Level Wind Shear Surface Winds Freezing Level lower Loop speed Faster ISSUED: 1445 UTC MON 26 APR 2010 Celling & I Visibility Turb High Turb Low Icing Obsch CL63/BR - - - LL Wind [LLWS € > Sfc Winds Frzg Lvl 0°: 120
• Mountain Obscuration (see Figure 5-13, G-AIRMET-Mountain Obscuration Snapshot Example).
• Areas of widespread mountain obscuration where Visual Meteorological Conditions (VMC) cannot be maintained, including the weather causing the obscuration. The weather causing the obscuration includes only CLDS, PCPN, FU, HZ, BR, and FG.
Figure 5-13. G-AIRMET-Mountain Obscuration Snapshot Example Ceiling & Visiblity Turb High Turb Low Icing Low Level Wind Shear Surface Winds Freezing Leve SueT Loop speed Faster · 26 APR 2H11 Turb High dộc Icing Mtn Sfc Winds → Frzg Lvl [0*: 120 5-25
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• Icing (see Figure 5-14, G-AIRMET—Icing Snapshot Example).
o Areas of moderate airframe icing, other than convectively induced, including the vertical extent (base and top). Altitude variations in the base of icing layers may be denoted (e.g., “080 / 060” indicates the altitude varies between 6,000 and 8,000 ft MSL).
Figure 5-14. G-AIRMET—Icing Snapshot Example
• Fre ezing Level (see Figure 5-15, G-AIRMET—Freezing Level Snapshot Example).
o Freezing level is defined as the lowest freezing level above the ground or at the SFC as appropriate. Freezing levels above the ground are delineated at 4,000 ft intervals MSL. Areas with multiple freezing levels above the ground are delineated including the vertical extent (base and top).
Figure 5-15. G-AIRMET-Freezing Level Snapshot Example Ceiling & Visiblity Turb High Turb Low Icing Mountain Obscuration Low Level Wind Shear Surface Winds Freezing Level Clear Slower Loop speed Faster Play 03Z APR ISSUED: 1445 UTC MON 26 APR 2018 Ceiling & Visibility Turb High Turb Low Icing Mtn SIc Winds ® Frzg Lvl 0": 120] tw Obscn
• Turbulence (see Figure 5-16, G-AIRMET-Turbulence-High Snapshot Example, and Figure 5-17, G-AIRMET-Turbulence-Low Snapshot Example).
o Areas of moderate turbulence, other than convectively induced, including the vertical extent (base and top).
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Figure 5-16. G-AIRMET-Turbulence-High Snapshot Example Ceiling & Visiblity Turb High Turb Low Icing Mountain Obscuration Low Level Wind Shear Surface Winds Freezing Level Slower Loop speed Faster 03Z
G-AIRME I UTC MON ISSUED: 1445 UTC MON 26 APR 201 Ceiling & Visibility Turb High Icing Mitn CLOS/ BR --- LL Wind [LLWS → Sfc Winds Frzg Lvl 0*: 120 Obscn Shear Figure 5-17. G-AIRMET-Turbulence-Low Snapshot Example Ceiling & Visiblity Turb High Turb Low Icing Mountain Obscuration Low Level Wind Shear Surface Winds Freezing Leve Slower Loop speed Faster Play 03Z G-AIRMET VALID: 1 UTC MON ISSUED: 1445 UTC MON 26 APR 2010 Ceiling & BR Visibility Turb High 280 Turb Low Icing ObSch CLbS/BR --- Mitn LL Wind [LLWS < Shea Stc Winds Frzg Lvl [0*: 120 5-28
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• Low-Level Wind Shear (LLWS) (see Figure 5-18, G-AIRMET—Low-Level Wind Shear (LLWS) Snapshot Example).
o LLWS is defined as windshear below 2,000 ft AGL, other than convectively induced, exceeding 10 kts per 100 ft (vector difference between two points in space).
Figure 5-18. G-AIRMET—Low-Level Wind Shear (LLWS) Snapshot Example
• Str ong Surface Winds (see Figure 5-19, G-AIRMET—Strong Surface Winds Snapshot Example).
o Areas of sustained surface winds greater than 30 kts. The direction and speed of winds are not depicted; only the area where sustained surface winds greater than 30 kts are occurring or forecast to occur.
5-30 Figure 5-19. G-AIRMET—Strong Surface Winds Snapshot Example
5.3.3 Use.
When using the G-AIRMET, users must keep in mind that if a 00-hour forecast shows no significant weather and a 03-hour forecast shows hazardous weather, they must assume a change is occurring during the period between the two forecasts. It should be taken into consideration that the hazardous weather starts immediately after the 00-hour forecast unless there is a defined initiation or ending time for the hazardous weather. The same would apply after the 03-hour forecast. The user should assume the hazardous weather condition is occurring between the snapshots unless informed otherwise.
5.4 Center Weather Advisory (CWA).
A 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 for aircrews to anticipate and avoid adverse weather conditions in the en route and terminal environments. CWAs are available on https://www.aviationweather.gov.
5.4.1 CWA Issuance.
CWAs are issued by the NWS Center Weather Service Units (CWSU). CWSU AORs are depicted on Figure 5-20, Center Weather Service Unit (CWSU) Areas of Responsibility.
5-31 Figure 5-20. Center Weather Service Unit (CWSU) Areas of Responsibility
C WAs are valid for up to 2 hours and may include forecasts of conditions expected to begin within 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.
5.4.2 CWA Criteria.
CWAs may be issued for the following situations:
• There is no existing AWC or AAWU advisory in effect.
• Any of the following conditions occur:
o Conditions meeting Convective SIGMET criteria.
o Icing—moderate or greater.
o Turbulence—moderate or greater.
o Heavy and extreme precipitation.
o Freezing precipitation.
o Conditions at or approaching low IFR (LIFR).
o Surface wind gust at or above 30 kts.
o LLWS (Surface—2,000 ft).
o Volcanic ash, duststorms, or sandstorms.
5-32 o When a hazard has grown significantly outside of the boundary defined by the AWC or AAWU advisory.
o To upgrade a thunderstorm advisory to include severe thunderstorms.
o To upgrade an AIRMET to include isolated severe turbulence or icing. If greater than isolated severe turbulence or icing is occurring, then a new (non-supplementary) CWA should be issued.
o To define a line of thunderstorms within a larger area covered by the AWC or AAWU advisory.
o To better define hazards expected at a major terminal already within an AWC or AAWU advisory.
o Anything that in the judgment of the CWSU forecaster will add value to an existing advisory.
• In the forecaster’s judgment the conditions listed above, or any others, may adversely impact the safe flow of air traffic.
5.4.3 CWA Format and Example.
Figure 5-21. Center Weather Advisory (CWA) Decoding Example