Definition
WS is the international identifier used on weather products and data feeds to label a SIGMET — a weather advisory issued for hazardous conditions affecting all aircraft, including severe icing, severe or extreme turbulence, dust storms, sandstorms, and volcanic ash that lower visibility to less than three miles. SIGMETs are non-convective; convective hazards are issued separately as Convective SIGMETs (designator WST).
Plain English
WS is the code stamped on a weather report to mark it as a SIGMET — an urgent warning about dangerous weather that can affect any aircraft flying through it.
Context Anchor
Seen in aviation weather briefings, flight planning tools, and weather updates before or during a flight.
Derivation
WS comes from the World Meteorological Organization data designator system, where W stands for warning and S for SIGMET. SIGMET itself is a contraction of SIGnificant METeorological information.
Why Pilots Care
Pilots review WS SIGMETs to decide whether to delay, reroute, or cancel a flight to avoid conditions that could damage the aircraft or cause loss of control.
Grounding Statement
If a WS — SIGMET covers your planned route, treat that area as a serious weather concern until you confirm it is safe for your aircraft and flight conditions.
Intuition Check
A WS — SIGMET is not just a routine weather note. It is issued for weather hazards serious enough to affect aircraft safety in flight.
Example Sentence 1
During the briefing, the dispatcher pointed out a WS covering severe turbulence over the route between Denver and Salt Lake City.
Example Sentence 2
A new WS SIGMET was issued for icing, so the crew added extra fuel for a lower altitude route.