FAA Aircraft Dispatcher (ADX)MeteorologyHard
While reviewing hazardous weather advisories, a dispatcher sees a report describing a line of thunderstorms 70 nautical miles long, with thunderstorms occupying 45 percent of the line's length, expected to persist for over an hour. Which advisory criteria does this meet?
- ASIGMET for volcanic ash
- BCenter Weather Advisory only, no SIGMET required
- CConvective SIGMET criteria for a line of thunderstorms
- DAIRMET Tango for turbulence
Show answer & explanationAnswer & explanation
Correct answer: C. Convective SIGMET criteria for a line of thunderstorms
A Convective SIGMET is issued for a line of thunderstorms at least 60 NM long affecting an area where thunderstorms occupy at least 40% of the line, expected to persist longer than 30 minutes. The described line (70 NM, 45% coverage, over an hour) meets all three criteria.
Why the other options are wrong
- A. Volcanic ash SIGMETs relate to eruptions and ash clouds, unrelated to thunderstorm lines.
- B. A Center Weather Advisory is a short-term local alert but does not replace the required Convective SIGMET when criteria are met.
- D. AIRMET Tango covers turbulence and low-level wind shear, not thunderstorm lines.
Convective SIGMET Criteria
Issued for severe thunderstorms, embedded/widespread thunderstorms affecting 40%+ of an area, or a line of thunderstorms 60+ NM long affecting 40%+ of the line.
- Valid for 2 hours, issued every hour as needed (55 min past)
- Implies severe or greater turbulence, severe icing, and low-level wind shear
- Criteria: line ≥60 NM, ≥40% coverage, hail ≥3/4in, or surface winds ≥50kt, or tornado
Memory trick: '60-40 rule': 60 NM long line, 40% coverage triggers a Convective SIGMET.