What is a SIGMET?
SIGMET (Significant Meteorological Information) warns of weather phenomena that are potentially hazardous to all aircraft, regardless of size or type. These are the highest-priority weather advisories in aviation.
SIGMET Phenomena
| Phenomenon | Description |
|---|---|
| Thunderstorms (OBSC TS, EMBD TS, SQL TS) | Thunderstorms: obscured, embedded in cloud, or squall line |
| Tropical cyclone (TC) | Hurricanes, typhoons, tropical storms |
| Severe turbulence (SEV TURB) | Turbulence hazardous to all aircraft |
| Severe icing (SEV ICE) | Icing that may exceed de-icing capability |
| Mountain waves (MTW) | Severe mountain wave activity |
| Volcanic ash (VA) | Airborne volcanic ash, extremely dangerous to jet engines |
| Dust/sandstorm (DS/SS) | Significant dust or sand storms reducing visibility |
| Radioactive cloud | Airborne radioactive material |
What is an AIRMET?
AIRMET (Airmen's Meteorological Information) warns of weather hazardous primarily to light aircraft and VFR pilots. While less severe than SIGMET conditions, AIRMETs should not be ignored by any pilot.
AIRMET Types (US System)
| Type | Code | Covers |
|---|---|---|
| Sierra | AIRMET S | IFR conditions, mountain obscuration |
| Tango | AIRMET T | Moderate turbulence, sustained surface winds 30+ kt |
| Zulu | AIRMET Z | Moderate icing, freezing level information |
What is GAMET?
GAMET (General Aviation Meteorological forecast) provides area forecasts for low-level flights (typically below FL100/FL150). It is the ICAO equivalent of the US AIRMET system and is used in many countries worldwide.
GAMET covers:
- Surface wind and visibility
- Significant weather phenomena
- Cloud coverage and base heights
- Icing and turbulence below FL100
- Mountain wave activity
- Freezing level
SIGMET vs. AIRMET Comparison
| Feature | SIGMET | AIRMET |
|---|---|---|
| Severity | All aircraft at risk | Light aircraft / VFR pilots |
| Validity | Up to 4 hours (6 for VA/TC) | 6 hours |
| Issued by | Meteorological Watch Office | Aviation Weather Center |
| Covers | Severe phenomena | Moderate phenomena |
| Priority | Highest | Advisory level |
Safety First
Active SIGMETs should be treated as a strong caution. Volcanic ash SIGMETs are absolute no-go zones for all aircraft. Always check for active SIGMETs along your route of flight before departure.Convective SIGMET (US Only)
In the United States, Convective SIGMETs are issued specifically for severe convective activity:
- Thunderstorms with surface winds 50+ knots
- Hail at the surface 3/4 inch or greater
- Tornadoes
- Embedded thunderstorms
- Lines of thunderstorms
- Thunderstorms with heavy precipitation affecting 40%+ of an area