FIG GEN 3.5.2
EFAS Radio Coverage Areas

NOTE.

EFAS radio coverage at 5000 feet AGL. The shaded areas depict limited coverage areas in which altitudes above 5000 feet AGL would be required to contact EFAS.
FIG GEN 3.5.3
 Inflight Advisory Plotting Chart

FIG GEN 3.5.4
Geographical Areas and Terrain Features

FIG GEN 3.5.5
Aviation Area Forecasts
FA Locations . Contiguous United States

FIG GEN 3.5.6
Alaska Area Forecast Sectors

FIG GEN 3.5.7
Hawaii Area Forecast Locations

3.9.3 SIGMET (WS)
3.9.3.1 A SIGMET advises of nonconvective weather that is potentially hazardous to all aircraft. SIGMETs are unscheduled products that are valid for 4 hours. However, conditions that are associated with hurricanes are valid for 6 hours. Unscheduled updates and corrections are issued as necessary. In the conterminous U.S., SIGMETs are issued when the following phenomena occur or are expected to occur:
 a) Severe icing not associated with thunderstorms.
 b) Severe or extreme turbulence or clear air turbulence (CAT) not associated with thunderstorms.
 c) Dust storms or sandstorms lowering surface or inflight visibilities to below 3 miles.
 d) Volcanic ash.
3.9.3.2 In Alaska and Hawaii, SIGMETs are also issued for: a) Tornadoes. b) Lines of thunderstorms.
 c) Embedded thunderstorms.
 d) Hail greater than or equal to 3/4 inch in diameter.

3.9.3.3 SIGMETs are identified by an alphabetic designator from November through Yankee exclud-ing Sierra and Tango. (Sierra, Tango, and Zulu are reserved for AIRMET text [WA] products; G.AIRMETS do not use the Sierra, Tango, or Zulu designators.) The first issuance of a SIGMET will be labeled as UWS (Urgent Weather SIGMET). Subsequent issuances are at the forecasters discre-tion. Issuance for the same phenomenon will be sequentially numbered, using the original designator until the phenomenon ends. For example, the first issuance in the Chicago (CHI) FA area for phenomenon moving from the Salt Lake City (SLC) FA area will be SIGMET Papa 3, if the previous two issuances, Papa 1 and Papa 2, had been in the SLC FA area. Note that no two different phenomena across the country can have the same alphabetic designator at the same time.
EXAMPLE.
Example of a SIGMET:

BOSR WS 050600 SIGMET ROMEO 2 VALID UNTIL 051000 ME NH VT FROM CAR TO YSJ TO CON TO MPV TO CAR MOD TO OCNL SEV TURB BLW 080 EXP DUE TO STG NWLY FLOW. CONDS CONTG BYD 1000Z.
3.9.3.4 Convective SIGMET (WST)
 a) Convective SIGMETs are issued in the conterminous U.S. for any of the following:
 1) Severe thunderstorm due to:
 (a) Surface winds greater than or equal to 50 knots.

(b) Hail at the surface greater than or equal to 3/4 inches in diameter.
 (c) Tornadoes.
 2) Embedded thunderstorms.
 3) A line of thunderstorms.
 4) Thunderstorms producing precipitation great-er than or equal to heavy precipitation affecting 40 percent or more of an area at least 3,000 square miles.
 b) Any convective SIGMET implies severe or greater turbulence, severe icing, and low.level wind shear. A convective SIGMET may be issued for any convective situation that the forecaster feels is hazardous to all categories of aircraft.
 c) Convective SIGMET bulletins are issued for the western (W), central (C), and eastern (E) United States. (Convective SIGMETs are not issued for Alaska or Hawaii.) The areas are separated at 87 and 107 degrees west longitude with sufficient overlap to cover most cases when the phenomenon crosses the boundaries. Bulletins are issued hourly at H+55. Special bulletins are issued at any time as required and updated at H+55. If no criteria meeting convective SIGMET requirements are observed or forecasted, the message “CONVECTIVE SIGMET... NONE” will be issued for each area at H+55. Individual convective SIGMETs for each area (W, C, E) are numbered sequentially from number one each day, beginning at 00Z. A convective SIGMET for a continuing phenomenon will be reissued every hour at H+55 with a new number. The text of the bulletin consists of either an observation and a forecast or just a forecast. The forecast is valid for up to 2 hours.
EXAMPLE.
Example of a Convective SIGMET:

MKCC WST 251655 CONVECTIVE SIGMET 54C VALID UNTIL 1855Z WI IL FROM 30E MSN.40ESE DBQ DMSHG LINE TS 15 NM WIDE MOV FROM 30025KT. TOPS TO FL450. WIND GUSTS TO 50 KT POSS.
CONVECTIVE SIGMET 55C VALID UNTIL 1855Z WI IA FROM 30NNW MSN.30SSE MCW DVLPG LINE TS 10 NM WIDE MOV FROM 30015KT. TOPS TO FL300. CONVECTIVE SIGMET 56C VALID UNTIL 1855Z MT ND SD MN IA MI LINE TS 15 NM WIDE MOV FROM 27020KT. TOPS TO FL380. OUTLOOK VALID 151855.252255 FROM 60NW ISN.INL .TVC.SBN .BRL .FSD . BIL.60NW ISN
IR STLT IMGRY SHOWS CNVTV CLD TOP TEMPS OVER SRN WI HAVE BEEN WARMING STEADILY INDCG A WKNG TREND. THIS ALSO REFLECTED BY LTST RADAR AND LTNG DATA. WKNG TREND OF PRESENT LN MAY CONT...HWVR NEW DVLPMT IS PSBL ALG OUTFLOW BDRY AND/OR OVR NE IA/SW WI BHD CURRENT ACT. A SCND TS IS CONTG TO MOV EWD THRU ERN MT WITH NEW DVLPMT OCRG OVR CNTRL ND. MT ACT IS MOVG TWD MORE FVRBL AMS OVR THE WRN DAKS WHERE DWPTS ARE IN THE UPR 60S WITH LIFTED INDEX VALUES TO MS 6. TS EXPD TO INCR IN COVERAGE AND INTSTY DURG AFTN HRS. WST ISSUANCES EXPD TO BE RQRD THRUT AFTN HRS WITH INCRG PTNTL FOR STGR CELLS TO CONTAIN LRG HAIL AND PSBLY DMGG SFC WNDS.
　
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