Chapter 26, Advisories 26-15
26.2.5.8.2 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 AWC (KKCI)
in Kansas City, MO, on the eighth day of the month at 1451 UTC. The NWS AWIPS communication header
for this product is SIGA0C. This is the eleventh issuance of SIGMET series Charlie valid from the eighth
day of the month at 1500 UTC until the eighth day of the month at 2100 UTC. Within the New York
Oceanic FIR, Tropical Cyclone Kyle observed at 31 °/6 minutes north, 71°/18 minutes west at 1500 UTC,
cumulonimbus tops to FL500 (approximately 50,000 ft MSL), within 120 NM of the center, moving from
west-southwest at 5 kt, no change in intensity is forecast, at 2100 UTC the tropical cyclone center will be
at 31°/42 minutes north, 70°/12 minutes west.
26.3 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. AIRMETs are intended to inform all pilots,
especially VFR pilots and operators of sensitive aircraft, of potentially hazardous weather phenomena.
AIRMETs contain details about IFR, extensive mountain obscuration, moderate turbulence, strong surface
winds, moderate icing, and freezing levels.
AIRMETs are intended for dissemination to all pilots in the preflight and en route phases of flight to
enhance safety. En route, AIRMETs are available over Flight Service frequencies. Over the CONUS,
AIRMETs are also available on equipment intended to disp lay weather and other non -ATC-related flight
information to pilots using the FIS -B. In Alaska and Hawaii, AIRMETs are broadcast on air traffic
frequencies.
AIRMETs are issued for the CONUS, Alaska, and Hawaii. No AIRMETs are issued for U.S. Oceanic FIRs
in the Gulf of America, Caribbean, and Western Atlantic and Pacific Oceans.
26.3.1 AIRMET Issuance
AIRMETs are issued from the three U.S. MWOs located at the AWC, the AAWU, and the WFO Honolulu.
Their areas of responsibility are:
• AWC: The CONUS and adjacent coastal waters.
• AAWU: Alaska and adjacent coastal waters.
• WFO Honolulu: Hawaii and adjacent waters.
26.3.1.1 AIRMETs Over the CONUS
AIRMETs over the CONUS are displayed graphically (sometimes known as G -AIRMETs) on websites
such as https://aviationweather.gov and https://www.1800wxbrief.com and equipment receiving FIS -B
information. AIRMETs over the CONUS provide a higher forecast resolution than AIRMETs issued in text
format. AIRMETs over the CONUS are valid at discrete times no more than three hours apart for a period
of up to 12 hours into the future ( e.g., 00, 03, 06, 09, and 12 hours). Additional forecasts may be inserted
during the first six hours (e.g., 01, 02, 04, and 05). A forecast at 00-hour represents the initial conditions,
and the subsequent graphics depict the area affected by the particular hazard at that valid time. Forecasts
valid at 00 through 06 hours correspond to the text AIRMET bulletin.
Chapter 26, Advisories 26-16
AIRMETs over the CONUS depict the following en route aviation weather hazards:
• IFR conditions (ceiling <1,000 ft and/or surface visibility <3 mi).
• Widespread mountain obscuration.
• Moderate icing.
• Freezing levels.
• Moderate turbulence.
• Non-convective LLWS potential below 2,000 ft AGL.
• Sustained surface winds greater than 30 kt.
Interpolation of time periods between AIRMETs over the CONUS valid times: Users should keep in mind
when using the AIRMET over the CONUS that if a 00 -hour forecast shows no significant weather and a
03-hour forecast shows hazardous weather, they must assum e 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. For example, if a 00-hour forecast
shows no hazard, a 03-hour forecast shows the presence of hazardous weather, and a 06-hour forecast shows
no hazard, the user should assume the hazard exists from the 0001-hour to the 0559-hour time period.
26.3.1.2 AIRMETs Over Alaska and Hawaii
AIRMETs over Alaska and Hawaii are in text format. The hazard areas are described using well -known
geographical areas. AIRMETs over Alaska are issued for three Alaska regions corresponding to Alaska
area forecasts.
AIRMETs over Alaska are valid up to eight hours. AIRMETs over Hawaii are valid up to six hours.
Unscheduled issuances contain an update number for easier identification.
There are three AIRMET categories: Sierra, Tango, and Zulu.
• AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations.
• AIRMET Tango describes moderate turbulence, sustained surface winds of 30 kt or greater,
and/or non-convective LLWS.
• AIRMET Zulu describes moderate icing and provides freezing level heights.
26.3.1.3 AIRMET Issuance Criteria
An AIRMET may be issued when any of the following weather phenomena are occurring or are expected
to occur:
• 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).
Chapter 26, Advisories 26-17
o Top and bottom of MOD TURB layer are specified.
• Sustained surface wind greater than 30 kt (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 AGL at intervals of 4,000 ft MSL (or surface (SFC) as appropriate) are
specified.
• Non-convective LLWS potential below 2,000 ft AGL (LLWS POTENTIAL).
26.3.2 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 Order JO 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 (METAR/SPECI). Refer to Federal Meteorological Handbook No. 1, Surface
Weather Observations and Reports, or Section 24.3 of this handbook.
26.3.3 AIRMET Issuance Times and Valid Periods
AIRMETs are issued following t he schedule listed in Table 26-4. AIRMETs are issued four 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 26-4. AIRMET Issuance Schedule
Product Type Issuance Time Issuance Frequency
AIRMETs over the CONUS 0245, 0845, 1445, 2045 UTC Every 6 hours
AIRMETs over Alaska
0115, 1315, 2115 UTC
(Standard Time)
0415, 1215, 2015 UTC
(Daylight Saving Time)
Every 8 hours
AIRMETs over Hawaii 0400, 1000, 1600, 2200 UTC Every 6 hours
AIRMETs are valid for six hours except for those in Alaska, which are valid for eight 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 hours
Chapter 26, Advisories 26-18
following the AIRMET ending time. Also, AIRMET bulletins can contain a separate outlook when
conditions meeting AIRMET criteria are expected to occur during the six-hour period (eight-hour for
Alaska) after the valid time of the AIRMET bulletin.
26.3.4 AIRMET Formats and Examples
The AWC’s website provides several options to display AIRMETs over the CONUS. 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 website.
An AIRMET message for Alaska and Hawaii 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.)
o AIRMET Sierra describes IFR 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 kt or greater,
and non-convective LLWS.
o AIRMET Zulu describes moderate icing and provides freezing-level heights.
• Fixed geographic locations (Alaska and Hawaii, see Figure 27-3 and Error! Reference source not
found.).
• 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.
• For Alaska AIRMETs: Intensity change remarks ( INTSF, WKN, IMPR, or NC) concerning the
continuance of the phenomenon following the valid period.
• For Hawaii AIRMETs: A separate AIRMET outlook is included in the AIRMET bulletin when
conditions meeting AIRMET criteria are expected to occur during the six-hour period after the
valid time of the AIRMET bulletin.
26.3.4.1 Example of AIRMET Sierra Issued for the Southeast Alaska Area
WAAK47 PAWU 241324
WA7O
JNUS WA 241315
AIRMET SIERRA FOR IFR AND MT OBSC VALID UNTIL 242115
.
LYNN CANAL AND GLACIER BAY JB
MTS OBSC BY CLDS/ISOL PCPN. NC.
.
CNTRL SE AK JC
MTS OCNL OBSC IN CLDS. NC.
.
SRN SE AK JD
Chapter 26, Advisories 26-19
PAWG-PAKT LN W OCNL CIGS BLW 010/VIS BLW 3SM BR. IMPR.
.
SRN SE AK JD
MTS OCNL OBSC IN CLDS. NC.
.
ERN GLF CST JE
OCNL CIGS BLW 010/VIS BLW 3SM BR/-RA BR. DTRT.
.
ERN GLF CST JE
MTS OBSC IN CLDS/ISOL PCPN. DTRT.
.
SE AK CSTL WTRS JF
MTS OCNL OBSC IN CLDS. NC.
.
=JNUT WA 241315
AIRMET TANGO FOR TURB/STG SFC WINDS VALID UNTIL 242115
.
ERN GLF CST JE
OFSHR ICY BAY W SUSTAINED SFC WND 30 KTS
OR GTR. SPRDG E. INTSF.
.
=JNUZ WA 241315
AIRMET ZULU FOR ICING VALID UNTIL 242115
.
ERN GLF CST JE
16Z TO 19Z ALG CST W ICY BAY OCNL MOD ICEIC 080-160.
FZLVL 045 EXC 015 INLAND. WKN.
Chapter 26, Advisories 26-20
26.3.4.2 Example of AIRMET Tango Issued for Hawaii FA Area
WAHW31 PHFO 241529
WA0HI
HNLS WA 241600
AIRMET SIERRA UPDATE 2 FOR IFR VALID UNTIL 242200
.
NO SIGNIFICANT IFR EXP.
=HNLT WA 241600
AIRMET TANGO UPDATE 3 FOR TURB VALID UNTIL 242200
.
AIRMET TURB...HI
OVER AMD IMT S THRU W OF MTN.
TEMPO MOD TURB BLW 070.
COND CONT BEYOND 2200Z.
=HNLZ WA 241600
AIRMET ZULU UPDATE 2 FOR ICE AND FZLVL VALID UNTIL 242200
.
NO SIGNIFICANT ICE EXP.
26.3.5 AIRMET Updates and Amendments
AIRMETs are issued over the CONUS by the AWC every six hours and are updated/amended as necessary.
If an AIRMET issued for Alaska or Hawaii is amended, “AMD” is added after the date/time group . The
issuance time of the AIRMET bulletin is updated to reflect the time of the amendment. The ending valid
time remains unchanged.
26.4 Center Weather Advisory (CWA)
A CWA is a concise description of the occurrence or expected occurrence of specified weather phenomena
that meet or approach in -flight advisory ( e.g., AIRMET, SIGMET, or Convective SIGMET) criteria. A
CWA is issued for hazardous weather when there is no existing in -flight advisory from the AWC or the
AAWU.
26.4.1 CWA Issuance
CWAs are issued by the NWS CWSU. CWSU areas of responsibility are depicted in Figure 26-8.
Chapter 26, Advisories 26-21
Figure 26-8. CWSU Areas of Responsibility
CWAs are valid for up to two hours and may include forecasts of conditions expected to begin within two
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 p henomenon. If the forecaster deems it necessary, CWAs may be issued hourly for convective
activity.
26.4.2 CWA Criteria
CWAs may be issued for the following situations:
• There is no existing AWC or AAWU advisory in effect or 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 LIFR;
o Surface wind gust at or above 30 kt;
o LLWS (surface–2,000 ft); or
o Volcanic ash, dust storms, or sandstorms.
• When a hazard has grown significantly outside of the boundary defined by the AWC or the AAWU
advisory.
• To upgrade a thunderstorm advisory to include severe thunderstorms.
• To upgrade an AIRMET to include isolated severe turbulence or icing. If greater than isolated
severe turbulence or icing is occurring, then a new CWA should be issued.