FAA Instrument Rating Airplane (IRA)Weather and Weather ServicesMedium
A TAF for a pilot's destination includes the entry 'PROB30 2022 1/2SM TSRA'. How should the pilot interpret this forecast element?
- AVisibility will improve to 1/2 statute mile within 30 minutes after 2000Z due to thunderstorms
- BThere is a 30 percent probability of thunderstorms with heavy rain and visibility 1/2 statute mile occurring between 2000Z and 2200Z
- CThere is a definite 30-minute period of thunderstorms and rain expected between 2000Z and 2200Z
- DThe main forecast conditions will be replaced entirely by thunderstorms after 2200Z
Show answer & explanationAnswer & explanation
Correct answer: B. There is a 30 percent probability of thunderstorms with heavy rain and visibility 1/2 statute mile occurring between 2000Z and 2200Z
PROB30 indicates a 30 percent probability of the specified conditions occurring during the stated time period; it is used for conditions such as thunderstorms that are not certain enough to be included in the prevailing forecast, and here it applies from 2000Z to 2200Z.
Why the other options are wrong
- A. The 2020–2022 group specifies a time range, not a 30-minute delay before improvement.
- C. PROB30 does not indicate a fixed duration event; it expresses a probability, not certainty.
- D. PROB groups indicate probability, not a certain replacement of prevailing conditions.
TAF PROB Group
A TAF probability group (e.g., PROB30 or PROB40) indicates the percent chance of specified weather conditions occurring during a stated time period.
- PROB30 = 30% chance; PROB40 = 40% chance
- Used for uncertain conditions like thunderstorms
- Not used within the first 6 hours of a TAF in some cases
Memory trick: PROB = probability, not promise.