c) These SIGMETs are considered “widespread” because they must be either affecting or be forecasted to affect an area of at least 3,000 square miles at any one time. The International SIGMET is issued for 6 hours for volcanic ash events, 6 hours for hurricanes and tropical storms, and 4 hours for all other events. Like the domestic SIGMETs, Interna-tional SIGMETs are also identified by an alphabetic designator from Alpha through Mike and are numbered sequentially until that weather phenome-non ends. The criteria for an International SIGMET are:
1) Thunderstorms occurring in lines, embedded in clouds, or in large areas producing tornadoes or large hail.
2) Tropical cyclones.
3) Severe icing.
4) Severe or extreme turbulence.
5) Dust storms and sandstorms lowering visibili-ties to less than 3 miles.
6) Volcanic ash.
EXAMPLE.
Example of an International SIGMET:
WSNT06 KKCI 022014 SIGA0F KZMA KZNY TJZS SIGMET FOXTROT 3 VALID 022015/030015 KKCI. MIAMI OCEANIC FIR NEW YORK OCEANIC FIR SAN JUAN FIR FRQ TS WI AREA BOUNDED BY 2711N6807W 2156N6654W 2220N7040W 2602N7208W 2711N6807W. TOPS TO FL470. MOV NE 15KT. WKN. BASED ON SAT AND LTG OBS. MOSHER
3.9.3.6 AIRMET (WA)
a) AIRMETs (WAs) are advisories of significant weather phenomena but describe conditions at intensities lower than those which require the issuance of SIGMETs. AIRMETs are intended for dissemination to all pilots in the preflight and en route phase of flight to enhance safety. AIRMET information is available in two formats: text bulletins (WA) and graphics (G.AIRMET). Both formats meet the criteria of paragraph 3.6.9.1 and are issued on a scheduled basis every 6 hours beginning at 0145 UTC during Central Daylight Time and at 0245 UTC during Central Standard Time. Unscheduled updates and corrections are issued as necessary. Each AIRMET Bulletin contains any current AIRMETs in effect and an outlook for conditions expected after the AIRMET valid period. AIRMETs contain details about IFR, extensive mountain obscuration, turbu-lence, strong surface winds, icing, and freezing levels.
b) There are three AIRMETs: Sierra, Tango, and Zulu. After the first issuance each day, scheduled or unscheduled bulletins are numbered sequentially for easier identification.
1) AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations.
2) AIRMET Tango describes moderate turbu-lence, sustained surface winds of 30 knots or greater, and/or nonconvective low.level wind shear.
3) AIRMET Zulu describes moderate icing and provides freezing level heights.
EXAMPLE. Example of AIRMET Sierra issued for the Chicago FA area:
CHIS WA 131445 AIRMET SIERRA UPDT 2 FOR IFR AND MTN OBSCN VALID UNTIL 132100. AIRMET IFR...KY FROM 20SSW HNN TO HMV TO 50ENE DYR TO20SSW HNN CIG BLW 010/VIS BLW 3SM PCPN/BR/FG. CONDS ENDG BY 18Z. . AIRMET IFR....MN LS FROM INL TO 70W YQT TO 40ENE DLH TO 30WNW DLH TO 50SE GFK TO 20 ENE GFK TO INL CIG BLW 010/VIS BLW 3SM BR. CONDS ENDG 15. 18Z. . AIRMET IFR....KS FROM 30N SLN TO 60E ICT TO 40S ICT TO 50W LBL TO 30SSW GLD TO 30N SLN CIG BLW 010/VIS BLW 3SM PCPN/BR/FG. CONDS ENDG 15.18Z. . AIRMET MTN OBSCN...KY TN FROM HNN TO HMV TO GQO TO LOZ TO HNN MTN OBSC BY CLDS/PCPN/BR. CONDS CONTG BYD 21Z THRU 03Z. .....
EXAMPLE. Example of AIRMET Tango issued for the Salt Lake City FA area:
SLCT WA 131445 AIRMET TANGO UPDT 2 FOR TURB VALID UNTIL 131200. AIRMET TURB...MT
FROM 40NW HVR TO 50SE BIL TO 60E DLN TO 60SW YQL TO 40NW HVR MOD TURB BLW 150. CONDS DVLPG 18.21Z. CONDS CONTG BYD 21Z THRU 03Z. . AIRMET TURB....ID MT WY NV UT CO FROM 100SE MLS TO 50SSW BFF TO 20SW BTY TO 40SW BAM TO 100SE MLS MOD TURB BTN FL310 AND FL410. CONDS CONTG BYD 21Z ENDG 21.00Z. . AIRMET TURB...NV AZ NM CA AND CSTL WTRS FROM 100WSW ENI TO 40W BTY TO 40S LAS TO 30ESE TBE TO INK TO ELP TO 50S TUS TO BZA TO 20S MZB TO 150SW PYE TO 100WSW ENI MOD TURB BTWN FL210 AND FL380. CONDS CONTG BYD 21Z THRU 03Z. ....
EXAMPLE. Example of AIRMET Zulu issued for the San Francisco FA area:
SFOZ WA 131445 AIRMET ZULU UPDT 2 FOR ICE AND FRZLVL VALID UNTIL 132100. NO SGFNT ICE EXP OUTSIDE OF CNVTV ACT. . FRZLVL....RANGING FROM SFC.105 ACRS AREA
MULT FRZLVL BLW 080 BOUNDED BY 40SE
YDC.60NNW GEG.60SW MLP.30WSW BKE.
20SW BAM.70W BAM.40SW YKM.40E HUH.
40SE YDC
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