FAA Private Pilot Helicopter (PRH)WeatherEasy
A helicopter pilot receives a Terminal Aerodrome Forecast (TAF) that includes the group 'PROB30 1820/1822 4SM -TSRA BKN030CB'. What is the probability of thunderstorms and rain occurring during the specified time period?
- AA 30% chance of thunderstorms and rain between 1800Z and 2200Z.
- BA 30% chance of thunderstorms and rain between 2000Z and 2200Z.
- CA 30% chance of thunderstorms and rain between 1800Z and 1822Z.
- DA 30% chance of thunderstorms and rain between 1800Z and 2000Z.
Show answer & explanationAnswer & explanation
Correct answer: B. A 30% chance of thunderstorms and rain between 2000Z and 2200Z.
The 'PROB30' group indicates a 30% probability of the described weather. The following '1820/1822' specifies the valid time period for this probability, meaning from 2000Z on the 18th to 2200Z on the 18th.
Why the other options are wrong
- A. The end time is correctly interpreted, but the start time is incorrect.
- C. The end time '1822' refers to 2200Z on the 18th, not the 22nd minute of the 18th hour.
- D. The time period is incorrectly interpreted; '1820' means the 20th hour of the 18th day, not between 1800Z and 2000Z.
TAF Probability Group (PROB)
In a TAF, a 'PROB' group indicates the probability of occurrence of specific weather conditions during a defined time period. 'PROB30' means a 30% chance, while 'PROB40' indicates a 40% chance. These groups are used for transient or intermittent conditions.
- Indicates likelihood, not certainty.
- Followed by a two-digit percentage (30 or 40).
- Includes a start and end time for the probability.
Memory trick: TAF PROB: Predicts Rare Occurrences of Bad Weather.