Non-Convective SIGMET (WS)

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):

Severe or extreme non-convective turbulence, or CAT not associated with thunderstorms

Severe icing not associated with thunderstorms

3. Widespread dust storms or sandstorms, lowering surface and/or flight visibilities to less than

three miles

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