A Convective SIGMET (WST) is issued for which conditions?
AAny thunderstorm activity regardless of intensity.
BSevere or embedded thunderstorms, lines of thunderstorms, or areas of thunderstorms covering 40% or more of 3,000+ square miles.✓
CAny cumulonimbus clouds reported within 50 miles of an airport.
Why →Convective SIGMETs are issued for: severe thunderstorms (surface winds ≥50 knots, hail ≥3/4 inch, or tornadoes), embedded thunderstorms, lines of thunderstorms at least 60 miles long, or areas of thunderstorms covering ≥40% of a 3,000+ sq mi area. They are valid for 2 hours and indicate conditions hazardous to all aircraft.
The trap →Not every thunderstorm qualifies: isolated ordinary cells may appear only in area forecasts. A Convective SIGMET means the severity thresholds were met.
Field note →For drone pilots, any nearby thunderstorm is a hard no-go, Convective SIGMET or not. Lightning strikes miles from the cell, and the associated wind shear and microbursts are unsurvivable for a small aircraft.
SOURCE → FAA Aviation Weather Services / PHAK Chapter 13CHECKED JUL 16ACS III.A.K1MED