SIGMET

SIGMETs (WSs) are broadcasted for hazardous weather that is considered of extreme importance to all aircraft. SIGMETs (acronym for "SIGnificant METeorological information") warn of the following weather hazards: severe icing, severe and extreme turbulence, dust storms, sandstorms, or volcanic ash lowering visibility to less than 3 miles. A Convective SIGMET (WST) is issued for hazardous convective weather (such as tornadoes, thunderstorms, hail) and covers severe or great turbulence, severe icing, and low-level wind shear.

A SIGMET (WS) example is shown below.

DFWA UWS 051710
SIGMET ALFA 1 VALID UNTIL 052110
AR LA MS
FROM MEM TO JAN
OCNL SVR ICING ABV FRZLVL EXPCD.
FRZLVL 080 E TO 120 W.
CONDS CONTIG BYD 2100Z.

Line 1
This is an urgent weather SIGMET (UWS) for the Dallas Fort Worth area issued on the 5th day of the month at 1900.

Line 2
This is the first issuance of this SIGMET (ALFA 1 and is valid until the 5th day of the month at 2110 (Note: The first report of a different weather hazard is noted by ALFA 1, with its second notice given the notation ALFA 2. The first report of a weather hazard different from the first one would have been labelled BRAVO with its second notice given the notation BRAVO 2.; The first report of a weather hazard different from the first two would have been labelled CHARLEY with its second notice given the notation CHARLEY 2.; that is alphabetical order beginning with A-B-C;

Line 3
This weather report is good for the Arkansas, Louisiana and Mississippi area.

Line 4
From Memphis, Tennessee to Jackson, Mississippi

Line 5
Occasional (OCNL) severe (SVR) icing above (ABV) freezing level (FRZLVL) expected (EXPCD)

Line 6
Conditions (COND) continuing (CONTG) beyond (BYD) 2100 Zulu time