Quantcast Non-Convective SIGMET (WS)

 

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CHAPTER THREE
METEOROLOGY FLIGHT PLANNING
Non-Convective SIGMET (WS)
A SIGMET advises of SIGnificant METeorological information other than convective activity that is
potentially hazardous to all aircraft. WSs are issued for the conterminous US by NAWAU and are
valid for up to 4 hours when any of the following weather phenomena occur or are forecast over an
area of at least 3000 square miles (Figure 3-5):
1.
Severe or extreme non-convective turbulence, or CAT not associated with thunderstorms
2.
Severe icing not associated with thunderstorms
3.  Widespread dust storms or sandstorms, lowering surface and/or flight visibilities to less than
three miles
4.
Volcanic eruption and ash clouds
Training Wing commanders are responsible for establishing local guidelines to ensure safety of
flight in and through areas where SIGMETs are in effect.
DFWP WS 051700
SIGMET PAPA 2 VALID UNTIL 052100
AR LA MS
FROM MEM TO 30N MEI TO BTR TO MLU TO MEM
MDT OCNL SEV ICE ABV FRZLVL EXP. FRZLVL 080 TO 120 W. CONDS CONTG BYD 2100Z
Figure 3-5 WS Example
The first issuance of any non-convective SIGMET will always be identified as an Urgent
SIGMET (UWS). Any subsequent issuance will be identified as WS unless the forecaster feels
the situation warrants using UWS to trigger more expeditious communications handling.
Each SIGMET is assigned a unique header to ensure computer systems can distribute and replace
the proper messages as required. Only the phonetic alphabet designators November, Oscar, Papa,
Quebec, Romeo, Uniform, Victor, Whiskey, X-ray, and Yankee are used for non-convective
SIGMETs (excludes those designators reserved for scheduled AIRMETs (Sierra, Tango, and
Zulu)). These designators will follow the area designator (SFO, SLC, CHI, DFW, BOS, and
MIA), which is used for distribution. It does not denote the office issuing the forecast; it denotes
the geographical area affected (e.g., DFWP in Figure 3-5).
The first time a SIGMET is issued for a phenomenon associated with a particular weather system,
it is given the next alphabetic designator in the series and is numbered as the first for that
designator (e.g., PAPA 1). Subsequent messages are numbered consecutively, using the same
designator (e.g., PAPA 2, PAPA 3, etc.) until the phenomenon ends or no longer meets SIGMET
criteria. In the conterminous US, this means a phenomenon assigned an alphabetic designator in
one area will retain that designator even if it moves into another area. For example, the first
issuance for a SIGMET moving into the DFW area from the SLC area might be SIGMET PAPA 4.
3-12
SEVERE WEATHER WATCHES, MILITARY ADVISORIES, AND PIREPS


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