METEOROLOGY FLIGHT PLANNING
Civilian stations will sometimes forecast the probability of occurrence of thunderstorms or other
precipitation events. Such a line begins with "PROB," followed by a 2-digit percentage and the
corresponding weather, as this example illustrates:
PROB40 1/2SM +TSRA OVC005CB
This station forecasts a 40% chance of heavy rain from thunderstorms, producing an overcast
ceiling of cumulonimbus clouds at 500 feet, with visibility ½ mile. Additionally, a 4-digit time
period group giving the beginning and ending time for the occurrence may follow this group.
USN/USMC stations will not use this change group.
Change Groups and Times (FROM/TO)
In order to use a TAF effectively, one must know how long a given pattern of weather will last,
as well as what that pattern will be. To do this, establish the FROM and TO times of that pattern.
In this text, TO will mean up TO, but not including that time.
The times on the first line of code, after the location, are the FROM and TO date and times for
the entire forecast, and the beginning (FROM) time of the first forecast line.
The time listed immediately after a FM can be a beginning time of a new pattern of weather as
well as a TO time of a previously defined pattern, depending upon where it falls in the forecast.
The first two digits of the 4-digit time group following BECMG will be the beginning (FROM)
time of the new forecast elements, and the last two digits are the ending (TO) time of the
The first two digits of the 4-digit time group shown after a TEMPO are the beginning (FROM)
time, and the last two digits are the ending (TO) time for that TAF line.
KNSE 200909 00000KT 0800 FG VV001 620106 QNH3000INS
TEMPO0912 00000KT 2400 BR SCT000 SCT005 SCT080 SCT250
FM1400 20005KT 6000 HZ SCT025 SCT080 SCT250 QNH3004INS
BECMG1617 9999 QNH3002INS
BECMG2022 23010KT 9999 SCT025 SCT080 BKN250 WSCONDS 531006 QNH2996INS
TEMPO2303 VRB15G30KT 1600 TSSH OVC010CB
Figure 1-31 From/To Example
1-26 AVIATION ROUTINE WEATHER REPORTS AND TERMINAL AERODROME