Definition
In aviation weather messaging, WS is the identifier used for a SIGMET — a weather advisory issued by the National Weather Service warning of weather phenomena considered hazardous to all aircraft, regardless of size. SIGMETs cover severe icing not associated with thunderstorms, severe or extreme turbulence or clear air turbulence not associated with thunderstorms, dust storms or sandstorms lowering visibility to less than three miles, and volcanic ash.
Plain English
WS is the code on a weather report that means a SIGMET has been issued — a warning to all pilots about serious weather like heavy icing, severe turbulence, dust storms, or volcanic ash that could be dangerous to any aircraft.
Context Anchor
Seen in aviation weather information, flight planning, and messages from air traffic control when weather may affect a route, airport, or area of flight.
Derivation
WS is the message header code used in international weather formats. The S in WS comes from SIGMET. SIGMET itself is a contraction of Significant Meteorological Information.
Why Pilots Care
Pilots must act on WS advisories to reroute, delay, or alter altitude and avoid conditions that could damage the aircraft or compromise control.
Intuition Check
Do not read “advisory” as “not important.” In aviation, a weather advisory is information meant to get your attention because the weather may affect safety or operations.
Example Sentence 1
The briefer noted a WS in effect for severe turbulence over the route, so we delayed departure by two hours.
Example Sentence 2
ATC relayed the WS indicating volcanic ash moving into the area, prompting an immediate diversion.