FAA Private Pilot Airplane (PAR)Weather Theory and ServicesHard
A TAF for KABC includes the group 'PROB30 2116/2119 1/2SM +TSRA'. How should a pilot interpret this forecast element?
- AThere is a 30 percent probability of thunderstorms with heavy rain and visibility reduced to 1/2 statute mile between 1600Z and 1900Z on the 21st
- BCeilings will be 300 feet with thunderstorms for 30 minutes starting at 1600Z on the 21st
- CThunderstorms are certain to occur, with a 30 percent chance of hail, between 1600Z and 1900Z on the 21st
- DThere is a 30 percent probability of a wind shift of 30 degrees occurring between 1600Z and 1900Z on the 21st
Show answer & explanationAnswer & explanation
Correct answer: A. There is a 30 percent probability of thunderstorms with heavy rain and visibility reduced to 1/2 statute mile between 1600Z and 1900Z on the 21st
The 'PROB30' group indicates a 30 percent probability of the conditions occurring during the specified time period. The time group '2116/2119' means the 21st day of the month from 1600Z to 1900Z, and '1/2SM +TSRA' means visibility of 1/2 statute mile in a thunderstorm with heavy rain.
Why the other options are wrong
- B. No ceiling value is given in this group, and the number 30 is not a duration in minutes.
- C. PROB30 means only a 30% chance the conditions occur, not that thunderstorms are certain.
- D. PROB30 refers to probability of forecast conditions, not a wind shift percentage.
TAF PROB Group
The PROB30 (or PROB40) group in a TAF indicates the percent probability that the specified weather conditions will occur during the given time period, expressed as day/hour to day/hour in UTC.
- PROB30/PROB40 = 30%/40% probability of occurrence
- Time format is DDHH/DDHH in UTC
- Used mainly for thunderstorms or low IFR conditions
Memory trick: PROB30 = Probably 30%, not for sure