AIM 

4/20/23 

3.  Date and Time of Origin. 

This element is the date and time the forecast is actually prepared. The format 

is a two

−

digit date and four

−

digit time followed, without a space, by the letter “Z.” 

4.  Valid Period Date and Time. 

The UTC valid period of the forecast consists of two four

−

digit sets, 

separated by a “/”. The first four

−

digit set is a two

−

digit date followed by the two

−

digit beginning hour, and the 

second four

−

digit set is a two

−

digit date followed by the two

−

digit ending hour. Although most airports have a 

24

−

hour TAF, a select number of airports have a 30

−

hour TAF. In the case of an amended forecast, or a forecast 

which is corrected or delayed, the valid period may be for less than 24 hours. Where an airport or terminal 

operates on a part

−

time basis (less than 24 hours/day), the TAFs issued for those locations will have the 

abbreviated statement “AMD NOT SKED” added to the end of the forecasts. The time observations are 

scheduled to end and/or resume will be indicated by expanding the AMD NOT SKED statement. Expanded 

statements will include: 

(a) 

Observation ending time (AFT DDHHmm; for example, AFT 120200) 

(b) 

Scheduled observations resumption time (TIL DDHHmm; for example, TIL 171200Z) or 

(c) 

Period of observation unavailability (DDHH/DDHH); for example, 2502/2512). 

5.  Forecast Meteorological Conditions. 

This is the body of the TAF. The basic format is: 

WIND/VISIBILITY/WEATHER/SKY CONDITION/OPTIONAL DATA (WIND SHEAR) 
The wind, visibility, and sky condition elements are always included in the initial time group of the forecast. 

Weather is included only if significant to aviation. If a significant, lasting change in any of the elements is 

expected during the valid period, a new time period with the changes is included. It should be noted that with 

the exception of a “FM” group the new time period will include only those elements which are expected to 

change, i.e., if a lowering of the visibility is expected but the wind is expected to remain the same, the new time 

period reflecting the lower visibility would not include a forecast wind. The forecast wind would remain the same 

as in the previous time period. Any temporary conditions expected during a specific time period are included 

with that time period. The following describes the elements in the above format. 

(a)  Wind. 

This five (or six) digit group includes the expected wind direction (first 3 digits) and speed 

(last 2 digits or 3 digits if 100 knots or greater). The contraction “KT” follows to denote the units of wind speed. 

Wind gusts are noted by the letter “G” appended to the wind speed followed by the highest expected gust. A 

variable wind direction is noted by “VRB” where the three digit direction usually appears. A calm wind (3 knots 

or less) is forecast as “00000KT.” 

EXAMPLE

−

 

18010KT  . . . . .  wind one eight zero at one zero (wind is blowing from 180). 

35012G20KT  . .  wind three five zero at one two gust two zero. 

(b)  Visibility. 

The expected prevailing visibility up to and including 6 miles is forecast in statute miles, 

including fractions of miles, followed by “SM” to note the units of measure. Expected visibilities greater than 

6 miles are forecast as P6SM (plus six statute miles). 

EXAMPLE

−

 

1

/

2

SM 

−

 visibility one

−

half 

4SM 

−

 visibility four 

P6SM 

−

 visibility more than six 

(c)  Weather Phenomena. 

The expected weather phenomena is coded in TAF reports using the same 

format, qualifiers, and phenomena contractions as METAR reports (except UP). Obscurations to vision will be 

forecast whenever the prevailing visibility is forecast to be 6 statute miles or less. If no significant weather is 

expected to occur during a specific time period in the forecast, the weather phenomena group is omitted for that 

time period. If, after a time period in which significant weather phenomena has been forecast, a change to a 

forecast of no significant weather phenomena occurs, the contraction NSW (No Significant Weather) will appear 

as the weather group in the new time period. (NSW is included only in TEMPO groups). 

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Meteorology