FAA Private Pilot Airplane (PAR)Weather Theory and ServicesHard
Which scenario meets the criteria that would prompt issuance of a Convective SIGMET for a line of thunderstorms?
- AThunderstorms producing surface wind gusts of 25 knots
- BA line of thunderstorms at least 60 nautical miles long affecting at least 40 percent of its length
- CA single isolated thunderstorm cell 20 miles in diameter producing moderate turbulence
- DA broken line of rain showers with occasional lightning covering a 30-mile area
Show answer & explanationAnswer & explanation
Correct answer: B. A line of thunderstorms at least 60 nautical miles long affecting at least 40 percent of its length
A Convective SIGMET is issued for a line of thunderstorms when the line is at least 60 nautical miles long and affects at least 40 percent of its length, in addition to criteria for embedded, severe, or tornado-producing thunderstorms and hail 3/4 inch or greater or surface winds of 50 knots or greater.
Why the other options are wrong
- A. 25-knot gusts fall below the 50-knot surface wind threshold required.
- C. An isolated single cell with only moderate turbulence does not meet convective SIGMET severity thresholds.
- D. Rain showers with occasional lightning over 30 miles don't meet the length or severity requirements.
Convective SIGMET Criteria
A Convective SIGMET is issued for severe or embedded thunderstorms, tornadoes, hail 3/4 inch or larger, surface winds of 50 knots or greater, or a line of thunderstorms at least 60 NM long affecting 40% of its length.
- Convective SIGMETs are issued for the continental U.S. only
- They imply the presence of severe turbulence, severe icing, and low-level wind shear
- Issued hourly with special updates as needed
Memory trick: '60 and 40' — 60 miles long, 40 percent coverage triggers the alert