As of 0800 UTC, July 1, 1996 , all terminal forecasts (FTs), for over 532 airports , in the U.S. are now being prepared and disseminated in the new international TAF code and all NWS-prepared FTs are discontinued.
Effective 0000 UTC January 1,1996, the changes to the Terminal Aerodrome Forecast (TAF) code described below were implemented by NWS offices who have TAF-issuance responsibility. A total of 102 TAFs were being produced by NWS offices. These code changes were implemented in conjunction with an international implementation of TAF code changes.
The implementation on January 1, 1996 and the addition of 12 new TAFs on February 1, 1996 represented interim steps in the complete domestic implementation of the TAF code in the United States.
1) VALID TIME GROUP:
The day of the month has been added (as a prefix) to the valid time group in the TAF. Specifically...the first two digits of the valid time group now represent the date of the month of the beginning of the valid period. The second two digits of the valid period indicate the beginning valid time (two-digit hour) in utc. The last two digits indicate the ending valid time (two-digit hour) in UTC.
EXAMPLE: EXPLANATION:
KCHS 020445Z 020606 TAF for Charleston AFB/Municipal issued
on the 2nd day of the month at 0445 UTC,
valid from 0600 UTC on the 2nd day of
the month until 0600 UTC on the next day
(the 3rd)
2) SIGNIFICANT PRESENT AND FORECAST WEATHER:
This change involves WMO Code Table 4678, i.e., significant present and forecast weather. Specifically, a new descriptor was added -- partial, coded as "PR". Partial is defined as "covering part of the aerodrome" and can only be used incombination with fog (i.e. PRFG) in both the METAR observationand the TAF forecast.
3) CLOUDS/SKY COVER:
A new sky cover contraction, "FEW" was introduced. "FEW" is defined as less than 1/8 to 2/8 sky cover. A corresponding change was made to the definition of "SCT (scattered)", which is now defined as 3/8 to 4/8 sky cover. The complete list of sky cover definitions is:
SKC - sky clear - no clouds;
FEW - - less than 1 okta to 2 oktas;
SCT - scattered - 3 to 4 oktas;
BKN - broken - 5 to 7 oktas; and
OVC - overcast - 8 oktas
EXAMPLE: EXPLANATION: FEW030 few clouds (less than 1/8 to 2/8) at 3000 feet
4) FORECAST CHANGE INDICATORS (SPECIFICALLY...THE FM GROUP):
The time (in UTC) in the FM (FROM) forecast change indicator group was expanded from a two-digit time indicating the hour of the change to a four-digit time, using two digits for hours and two digits for minutes. Note that the FM group shall always include a four-digit time. While the use of a four-digit time in whole hours (e.g., 2300 UTC) remains acceptable, if a forecaster can predict changes and/or events with higher resolution, minutes (e.g. 2315 UTC) should be used. The use of minutes is allowed only for the change indicator FMgggg, meaning "FROM" and the 2-digit hour and 2-digit minute (in UTC).
EXAMPLES: EXPLANATIONS: FM0320 significant change at 0320 UTC FM0500 significant change at 0500 UTC
5) FORMATTING CHANGES
- each FM group shall begin on a separate line...Indented 5 spaces from the left margin;
- continuation lines shall be indented 6 spaces from the left margin. NOTE: Some NWS-prepared TAFs may include continuation lines which are indented 5 spaces rather than 6 spaces between January 1, 1996 and July 1, 1996. This is due to a limitation in the software some NWS offices use to prepare the TAFs, based on FTs. After July 1, 1996, all continuation lines in NWS-prepared TAFs shall be indented six spaces;
- An end-of-report separator ("=") shall be included at the end of each TAF.
EXAMPLE INCLUDING FORMATTING CHANGES:
TAF
PAOM 071045Z 071212 14004KT P6SM FEW030
FM2100 14010KT P6SM SCT030 PROB40 2106 2SM -RA
OVC020
FM0600 21015KT P6SM SCT035=
With the complete implementation of the METAR and TAF codes in the U.S. on July 1, 1996, one additional group is being implemented in the TAF code -- the forecast of non-convective low-level wind shear -- in the format described below.
The non-convective low-level (up to 2000 feet above the ground) wind shear group (WShwshwshws/dddffKT) shall be included in North American TAFs only. There is no provision in the international TAF code for non-convective low-level wind shear (LLWS). In the United States, the non-convective LLWS group will be included, when conditions are expected, immediately following the cloud forecast group in the TAF. In Canadian TAFs, the non-convective LLWS group, while coded in the same format as in the U.S, will appear in a different location -- immediately following the surface wind forecast.
In both the U.S. and Canada, the non-convective LLWS group shall be coded and decoded as follows:
WSh h h /dddffKT
ws ws ws
WS - an indicator for low-level non-convective
wind
shear;
h h h - forecast height, in hundreds of feet above ground
ws ws ws level, of the wind shear;
ddd - forecast wind direction, tens of degrees true,
above the shear;
ff - forecast wind speed, in knots, above the shear;
KT - units indicator, meaning knots
EXAMPLE: EXPLANATION:
WS015/30035KT forecast wind shear at 1500 feet AGL; wind from
300 degrees at 35 knots
SAMPLE U.S. TAF:
TAF
KGEG 231051Z 231212 12012KT 4SM -RA BR OVC008
WS005/27050KT TEMPO 1719 1/2SM -RA FG
FM1930 09012KT 1SM -DZ BR VV003 BECMG 2021 5SM HZ
FM2200 23020KT P6SM BKN020
FM0000 24015KT P6SM SCT050=
On July 1, 1996, a new TAF chapter, D-31, entitled "Aviation Terminal Forecasts" became effective. A Draft version of WSOM chapter D-31 is available for FTP Download Only on the METAR/TAF information page.