FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesMedium
A pilot planning a flight through a mountainous region is briefed on a SIGMET (non-convective) for the route. Which of the following conditions would warrant this SIGMET?
- ASevere icing not associated with thunderstorms
- BIsolated thunderstorms with tops to 25,000 feet
- CModerate turbulence below 15,000 feet
- DCeilings below 1,000 feet with visibility below 3 miles
Show answer & explanationAnswer & explanation
Correct answer: A. Severe icing not associated with thunderstorms
A non-convective SIGMET is issued for hazards affecting all aircraft such as severe icing, severe turbulence, dust or sandstorms reducing visibility below 3 miles, and volcanic ash — all not directly associated with thunderstorms. Thunderstorm-related hazards are covered by Convective SIGMETs instead.
Why the other options are wrong
- B. Thunderstorm activity, even isolated, is covered by a Convective SIGMET, not a standard SIGMET.
- C. Moderate turbulence is covered by an AIRMET (Tango), not a SIGMET, which requires severe turbulence.
- D. Widespread low ceilings and visibility are covered by AIRMET Sierra, not a SIGMET.
Non-Convective SIGMET
A weather advisory for hazardous conditions significant to all aircraft, including severe icing, severe turbulence, dust/sandstorms, and volcanic ash, not associated with thunderstorms.
- Valid for 4 hours (7 hours for volcanic ash/hurricanes)
- Covers severe (not moderate) icing and turbulence
- Separate from Convective SIGMET, which covers thunderstorm hazards
Memory trick: SIGMET = Severe stuff, not storms; Convective SIGMET = storms specifically.