A dispatcher is reviewing thunderstorm activity and must determine whether a Convective SIGMET should be issued. Which of the following meets the criteria for issuance of a Convective SIGMET?
- AAn isolated single-cell thunderstorm producing light rain and no reported hazards
- BA cumulus cloud with light-to-moderate turbulence and no lightning
- CA line of thunderstorms at least 60 miles long affecting at least 40 percent of its length
- DScattered cumulonimbus clouds producing tops below 15,000 feet with no severe weather
Show answer & explanationAnswer & explanation
Correct answer: C. A line of thunderstorms at least 60 miles long affecting at least 40 percent of its length
Convective SIGMETs are issued for: severe thunderstorms with surface winds ≥50 knots, hail ≥3/4 inch, or tornadoes; embedded thunderstorms; a line of thunderstorms at least 60 nautical miles long affecting at least 40% of its length; or thunderstorms affecting 40% or more of a 3,000-square-mile area. A single benign cell or scattered non-severe cumulonimbus does not meet the criteria.
Why the other options are wrong
- A. An isolated non-severe thunderstorm does not meet Convective SIGMET criteria.
- B. Simple turbulence in a cumulus cloud without severe convective weather does not qualify.
- D. Low-topped, non-severe cumulonimbus without severe weather elements does not meet the criteria.
Convective SIGMET
A weather advisory issued for significant convective activity such as severe thunderstorms, embedded thunderstorms, lines of thunderstorms, or widespread thunderstorm coverage.
- Issued for severe thunderstorms with tornado, hail ≥3/4 in, or wind gusts ≥50 kt
- Issued for a line of storms ≥60 NM long affecting ≥40% of its length
- Issued for thunderstorms affecting ≥40% of a 3,000 sq mi area
Memory trick: 60 miles long, 40 percent strong — that's when Convective SIGMETs get sung