Definition
WST is the identifier code used on weather products for a Convective SIGMET — an in-flight weather advisory issued for hazardous convective activity that is significant to the safety of all aircraft. Convective SIGMETs are issued for severe thunderstorms with surface winds of 50 knots or greater, hail at the surface 3/4 inch in diameter or greater, tornadoes, embedded thunderstorms, lines of thunderstorms, or thunderstorms covering 40 percent or more of an area of at least 3,000 square miles.
Plain English
WST is the code that marks a weather warning about dangerous thunderstorm activity. When you see WST on a weather product, it's telling you a Convective SIGMET has been issued because thunderstorms in that area are bad enough to threaten any aircraft.
Context Anchor
You may see WST in aviation weather information, flight planning materials, or pilot/controller glossary references where weather alerts are being identified by short codes.
Derivation
The letters W-S-T are the standard ICAO/FAA product code for Convective SIGMET. The 'W' aligns with weather/warning products, and the code distinguishes it from a regular SIGMET (WS) and AIRMET (WA). It's a routing tag, not a word — but recognizing WST on a printout immediately tells you 'convective SIGMET, take it seriously.'
Why Pilots Care
These advisories help pilots avoid weather that could cause turbulence, icing, or loss of control.
Intuition Check
Do not read “advisory” as casual advice that can be ignored. In aviation, a weather advisory is an official alert that the weather may affect safety, even though it is not an air traffic control clearance or command.
Example Sentence 1
During the preflight briefing, the pilot noticed a WST in effect for the route and chose to delay departure until the line of thunderstorms moved through.
Example Sentence 2
An updated WST prompted the crew to climb to a higher altitude to avoid reported icing.