What Does PROB30 Mean in a TAF?
PROB30 means a 30% probability of the conditions during the period: possible, not expected. It stands for PROBability 30%.
PROB30 in a real report
PROB30 0604/0608 1SM TSRA
What it changes for you
PROB30 is the only stated uncertainty in the whole TAF format. Everything else
is written flat. That does not make the rest certain.
A 30 percent chance of conditions below your minimums is not a long shot. The forecaster wrote it down because it is live.
The combined form
PROB30 TEMPO 2902/2906 1SM FG is common. It reads as a 30 percent chance of
temporary fog in that window. Both qualifiers apply, so it is neither certain nor
sustained.
Where you will not see it
A PROB group never appears in the first block of a TAF. The opening conditions
are a straight forecast, not a probability.
It also never attaches to a BECMG group. Combining a gradual transition with a
probability would be too vague to act on, so the format does not allow it.
Related codes
Decode a report containing this code
Paste a METAR, TAF, PIREP or SIGMET into the WxDecoder decoder. Every group comes back in plain English. The raw code sits beside it, so you can check the decode rather than trust it.
Frequently asked questions
What does PROB30 mean in a TAF?
A 30 percent probability of the conditions that follow, during the period given. It is possible rather than expected, and it is the forecaster's way of flagging a real but minority outcome.
Why is there no PROB50 or PROB20?
Below 30 percent the forecaster says nothing, because it is not worth qualifying. At 50 percent or more, a probability is a coin flip and the conditions would be forecast directly with a change group instead.