There are 5 in-flight weather advisories that are forecast based on actual weather conditions.
1. Convective sigmet [WST]
- advises of weather that is convective in nature and is issued for every thunderstorms with hail greater than 3/4“, surface winds greater than 50 knots
- tornadoes, embedded thunderstorms, lines of thunderstorms
- thunderstorm producing precipitation
- Convective sigmet also implies severe turbulence, icing, and low-level wind shear
- valid for 2 hours
2. Sigmet [WS]
- advises of non-convective weather that is potentially hazardous to all aircrafts
- issued for severe turbulence and icing not associated with convective activity, dust storms and sand storms reducing visibility below 3SM, and volcanic ash
- valid for 4 hours
3. Airmet [WA]
- advises of weather that is lower in intensity
- valid for 6 hours
- there are 3 types of Airmet
Sierra – IFR or mountain obscurations.
Tango – moderate turbulence, sustained surface wind of 30 knots or greater, and non-convective low-level wind shear.
Zulu – moderate icing.
4. CWA(Center Weather Advisories)
- is issued on an unscheduled basis as supplementary information to an existing WA, WS, or WST
- valid for 2 hours
5. WW(Severe Weather Watch Bulletins) / AWW(Alert Weather Watch Bulletins)
- issued in areas of severe thunderstorm or tornado activity
- severe activity is defined by greater than 3/4“ hail, wind gusts greater than 50 knots
- a tornado watch defines an area where possible tornado activity exists
June-Young Lee 