JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
Temperature Group
This is an optional group; however, its usage is highly encouraged and should be included to
meet the requirements of local operations, especially for helicopter and VSTOL aircraft, which
require density altitude. The forecast maximum or minimum temperature, depending on the time
of the day, is given in two digits Celsius, using “M” for minus temperatures. This is followed by
the 2-digit hour during which the maximum or minimum is expected to occur. It will be on the
last line of the TAF, unless the forecast was amended.
Change Group Terminology
The change groups of “FM,” “BECMG,” and “TEMPO” will be used whenever a change in
some or all of the elements forecasted are expected to occur at some intermediate time during the
24-hour TAF period. A new line of forecasted text is started for each change group. More than
one change group may be used to properly identify the forecast conditions (Figure 6-22).
FM (From) and BECMG (Becoming) are indicators of expected speed of change. FM is used
when the change is expected to be quick, and BECMG is used when the change is expected to
occur over a longer period of time. FM indicates that a permanent, dramatic or relatively
dramatic, change to a weather pattern is forecast to occur in a short period. All elements of the
forecast conditions will be listed on that TAF line. BECMG indicates that some forecast
elements are going to change permanently, or possibly that all of the forecast elements are to
change. TEMPO (Temporary) means just that: a temporary or non-permanent change to the to
the overall weather pattern.
KNSE TAF 260909 28004KT 9000 HZ SCT020 SCT200 QNH2998INS
FM1200 26007KT 9000 HZ SCT025 SCT080 BKN250 QNH2996INS
VCSHRA
BECMG 1416 9999 SCT025CB SCT250
BECMG 1718 23015G25KT 530004
TEMPO 1902 8000 TSSHRA SCT010 BKN025CB
FM0200 27010KT 9999 SCT030 BKN080 BKN250 QNH3001INS 20/09Z
Figure 6-22 — TAF Change Groups
FM Group
The heading “FM” followed immediately by a time (hours and minutes) indicates that the
forecast weather is expected to change rapidly to the conditions on that line. In other words, the
time indicates the beginning of a significant and permanent change in the whole weather pattern,
and all previously forecast conditions are superseded by the conditions forecasted on this line.
Additionally, the “FM” line includes all elements of a normal forecast as discussed above.
Using Figure 6-22 as an example, the change group “FM1200” starts the change line, and this
indicates a change is forecasted to occur at 1200Z. All elements on that line will be in effect
6-20 Version 3.2/Dec 08