FAA Commercial Pilot Airplane (CAX)WeatherMedium
A pilot is advised of a 'PROB40 1/2SM FG' in the Terminal Aerodrome Forecast (TAF) for the destination airport. In the context of aviation weather forecasting, what does 'PROB40' specifically indicate?
- AThe weather condition has a probability of occurring within 40 nautical miles of the airport.
- BVisibility will be 40 statute miles, or less, due to fog.
- CThe specified weather condition is expected to last for 40 minutes.
- DThere is a 40% chance that the specified weather condition will occur.
Show answer & explanationAnswer & explanation
Correct answer: D. There is a 40% chance that the specified weather condition will occur.
'PROB40' in a TAF indicates a 40 percent probability that the specified weather conditions (1/2SM FG) will occur during the forecast period. It is not an indicator of duration, visibility, or distance.
Why the other options are wrong
- A. Distance is indicated by 'VC' (vicinity) or specific coordinates, not 'PROB'.
- B. 'PROB40' is a probability, not a visibility value. Visibility is '1/2SM'.
- C. Duration is typically indicated by 'TEMPO' or time groups, not 'PROB'.
TAF Probability (PROB)
A TAF forecast group indicating the probability of specific weather conditions occurring.
- Reported as 'PROB' followed by a percentage (e.g., PROB30, PROB40).
- Indicates a chance of conditions, not a certainty.
- Significant for flight planning, especially for marginal VFR/IFR conditions.
Memory trick: PROB is the 'prob'ability of bad weather; it's a chance, not a sure thing.