FAA Private Pilot Airplane (PAR)Weather Theory and ServicesMedium
A TAF for an airport includes the group 'FM2100 22015G25KT P6SM SCT030'. What does the 'FM2100' portion indicate to the pilot?
- AThe forecast is valid only from 2100Z until the end of the TAF period
- BA temporary fluctuation in conditions expected for one hour starting at 2100Z
- CA 30% probability of the described conditions occurring at 2100Z
- DA rapid and significant change in conditions expected beginning at 2100Z, replacing the previous forecast group
Show answer & explanationAnswer & explanation
Correct answer: D. A rapid and significant change in conditions expected beginning at 2100Z, replacing the previous forecast group
The 'FM' (from) group in a TAF marks a rapid, significant, and usually permanent change in conditions expected at the indicated time; it completely replaces the prior forecast group rather than being temporary or probabilistic.
Why the other options are wrong
- A. FM only marks the start of a change; it does not necessarily mean it is the final period of the TAF unless another FM/BECMG follows.
- B. Temporary fluctuations are indicated by 'TEMPO,' not 'FM.'
- C. Probability groups are indicated by 'PROB30' or 'PROB40,' not 'FM.'
TAF FM Group
In a Terminal Aerodrome Forecast, 'FM' followed by a time indicates a rapid, significant change in prevailing conditions that begins at that time and completely replaces the previous forecast group.
- FM = From, marks abrupt permanent-type change
- BECMG = Becoming, gradual change over a time range
- TEMPO = Temporary, fluctuations lasting less than an hour at a time
- PROB30/40 = probability of thunderstorms or other conditions
Memory trick: FM = Fast/Full change; BECMG = Bit-by-bit; TEMPO = Temporary blip