SIGMETs and AIRMETs explained
The difference between AIRMETs and SIGMETs, the hazards each covers, and how to use them.
AIRMETs and SIGMETs are in-flight advisories warning of weather hazardous to aircraft over a wide area. The difference is severity.
AIRMETs (Airmen's Meteorological Information) cover conditions hazardous mainly to light aircraft and VFR pilots, issued in three types:
- Sierra — IFR conditions and mountain obscuration.
- Tango — moderate turbulence and surface winds 30+ knots.
- Zulu — moderate icing and freezing levels.
SIGMETs (Significant Meteorological Information) cover conditions hazardous to all aircraft:
- Non-convective SIGMETs — severe turbulence, severe icing, dust/sandstorms or volcanic ash reducing visibility below 3 miles.
- Convective SIGMETs — thunderstorm-related hazards: lines of storms, embedded storms, or areas of heavy precipitation; these imply severe turbulence, icing, hail and wind shear and are issued hourly (more often as needed).
Both define an area, altitudes, and a valid time, and are available in your briefing and on the Aviation Weather Center site. The practical use: an AIRMET Zulu over your route says *expect icing — verify the freezing level and have an out*; a Convective SIGMET says *avoid the area entirely*. They're broad-brush by design, so combine them with radar, PIREPs and current observations to decide whether to go, divert, or wait.
*Reference and training only. Use official briefings for flight planning.*