4.5 PROB30 Group
The probability group, PROB30, is used to forecast a low probability (30% chance) of a thunderstorm or precipitation event and its associated weather and/or obscuration elements.
Format: The contraction, PROB30 is followed by a space, then eight (8) digits. The first four (4) digits represent the day of the month and the beginning time in UTC of the expected event. The last four (4) digits represent the day of the month and the ending time in UTC of the event. (Note: There is a forward slash that separates the starting and ending day/time groups).
Example:
The PROB30 group will be located within the same line as the prevailing condition group, continuing on the line below if necessary. Only one PROB30 group will be used following any subsequent FM groups.
Key points when using PROB30
- The PROB30 group will not be used in the first nine (9) hours of the TAF's valid period. The time period covered by the PROB30 group should generally be six (6) hours or less.
- If a thunderstorm or precipitation event probability is expected to equal or exceed 50%, then use a FM or TEMPO group to forecast the event.
- PROB30 is the only PROB group used in NWS TAFs.
- The PROB30 group may not be used by NWS offices as a direct modifier of the TEMPO group (i.e., PROB30 TEMPO 2324...). Similarly, the TEMPO groups may not be used as a direct modifier of the PROB30 group (i.e., TEMPO PROB30 2324).