Supplemental Information for
Service Change Notice 08-15
 
Service Change Notice 08-15 (txt)
Background and List of Participating US Airports (doc)
30-Hour TAF Information
 
Format Change for Terminal Aerodrome Forecasts (TAFs) From 24 Hour Format to 30 Hour Format: Effective November 5 2008.


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Decoding the new TAF Format

On November 5, 2008, with the 1800 UTC issuance, the NWS will change the TAF format to conform to international standards outlined in ICAO Annex 3. The change includes the initiating of 30-hour TAFs for high-impact U.S. airports. To accommodate the extended TAF period, the format of all TAFs will change.
The change involves identifying the date associated with each time group. As shown in the example below, the previous TAF code is modified by adding the appropriate date before the forecast hour.
Example of 30-hour TAF:
TAF
KXXX 241732Z 2418/2524 (1)11006KT 4SM -SHRA BKN030
     FM242300(2) 22006KT 3SM -SHRA OVC030 PROB30 2504/2506 (3)
          VRB20G35KT 1SM +TSRA BKN015CB
     FM 250600 250010KT 4SM -SHRA OVC050
          TEMPO 2508/2511(4) 2SM -SHRA OVC030=
(1) Valid Period Indicates the valid time of the 30-hour TAF where 2418 is the 24th day at 1800 UTC and 2524 is the 25th day at 2400 UTC (or 0000 UTC on the 26th).

(2) FM Change Group Indicates a significant and rapid change to a new set of prevailing conditions in this case starting at 2300 UTC on the 24th.

(3) PROB30 Indicates the probability of occurrence of a thunderstorm or other precipitation event in this case occurring during the two-hour period between 0400 UTC and 0600 UTC on the 25th.

(4) TEMPO Change Group Indicates a temporary fluctuation in forecast conditions in this case in the two-hour period between 0800 UTC and 0011 UTC on the 25th

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Examples

The change affects the date/time groups in the TAFs. The valid time of a TAF becomes ddhh/ddhh from the present ddhhhh. TEMPOs and PROBS will also change, hhhh in both groups' changes to ddhh/ddhh. FROM groups change from hhmm to ddhhmm.
 
dd is the date of the month ie 17 or 17th.
hh is the hour ie 22 or 2200GMT
mm is minutes 15 or 15 minutes after the hour
 
Example: The present form
KABC 131128Z 131212 14005KT P6SM SCT025 OVC040
          TEMPO 1216 OVC025
     FM1600 13015G23KT P6SM OVC015
     FM2100 13015G22KT P6SM OVC008
          TEMPO 2101 1SM -SN
     FM0100 09015KT 3SM BR OVC006
          TEMPO 0105 2SM -SN BLSN
     FM0500 01015KT 5SM BR OVC006=
 
            Becomes ...

            30-hr TAF
KABC 131128Z 1312/1418 14005KT P6SM SCT025 OVC040
          TEMPO 1312/1316 OVC025
     FM131600 13015G23KT P6SM OVC015
     FM132100 13015G22KT P6SM OVC008
          TEMPO 1321/1401 1SM -SN
     FM140100 09015KT 3SM BR OVC006
          TEMPO 1401/1405 2SM -SN BLSN
     FM141500 01015KT 5SM BR OVC006=
 
            Or ...

            24-hr TAF
KABC 131128Z 1312/1412 14005KT P6SM SCT025 OVC040
          TEMPO 1312/1316 OVC025
     FM131600 13015G23KT P6SM OVC015
     FM132100 13015G22KT P6SM OVC008
          TEMPO 1321/1401 1SM -SN
     FM140100 09015KT 3SM BR OVC006
          TEMPO 1401/1405 2SM -SN BLSN
     FM140500 01015KT 5SM BR OVC006=

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