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AIM

10/12/17

7−1−71

Meteorology

EXAMPLE−

FM210100 14010KT P6SM SKC − “after 0100Z on the

21st, wind one four zero at one zero, visibility more than six,

sky clear.”

2. Becoming (BECMG) group. The BECMG

group is used when a gradual change in conditions is

expected over a longer time period, usually two

hours. The time period when the change is expected

is two four−digit groups separated by a “/”, with the

beginning date and hour, and ending date and hour of

the change period which follows the BECMG

indicator. The gradual change will occur at an

unspecified time within this time period. Only the

changing forecast meteorological conditions are

included in BECMG groups. The omitted conditions

are carried over from the previous time group.

NOTE−

The NWS does not use BECMG in the TAF.
EXAMPLE−

OVC012 BECMG 0114/0116 BKN020 − “ceiling one

thousand two hundred overcast. Then a gradual change

to ceiling two thousand broken between 1400Z on the 1st

and 1600Z on the 1st.”

3. Temporary (TEMPO) group. The TEMPO

group is used for any conditions in wind, visibility,

weather, or sky condition which are expected to last

for generally less than an hour at a time (occasional),

and are expected to occur during less than half the

time period. The TEMPO indicator is followed by

two four−digit groups separated by a “/”. The first

four digit group gives the beginning date and hour,

and the second four digit group gives the ending date

and hour of the time period during which the

temporary conditions are expected. Only the

changing forecast meteorological conditions are

included in TEMPO groups. The omitted conditions

are carried over from the previous time group.

EXAMPLE−
1. SCT030 TEMPO 0519/0523 BKN030 − “three
thousand scattered with occasional ceilings three thousand
broken between 1900Z on the 5th and 2300Z on the 5th.”

2. 4SM HZ TEMPO 1900/1906 2SM BR HZ − “visibility
four in haze with occasional visibility two in mist and haze
between 0000Z on the 19th and 0600Z on the 19th.”