5.4 Amended TAFs
An amended (updated) TAF is issued because weather conditions at the TAF site are changing earlier or later than what the current forecast indicates.
TAFs will be amended when:
Conditions meeting amendment criteria are imminent or have occurred and those conditions are expected to persist for 30 minutes or longer.
or
New information indicates future weather conditions are expected to be in a different flight category than originally forecast, particularly in the 1 to 6 hour time period.
You should make every attempt to update TAFs prior to the onset of changes you feel are unrepresentative of existing or expected conditions, particularly with unforeseen weather changes that can cause huge delays in the National Airspace System (NAS).
The amended TAF is identified in the WMO header using the contraction "AAx" as discussed in Lesson 5.3 Formats. Along with the WMO header coding, contraction "TAF AMD" is placed on the first line of the forecast text.
Example:
| Original TAF | Amended TAF |
| FTUS42 KMFL 141100 TAF KMFL 141136Z 1412/1512... |
FTUS42 KMFL 141100 AAA TAF AMD KMFL 141409Z 1414/1512... |
The above KMFL TAF was originally issued at 1136 UTC on the 14th day of the month. The TAF was amended at 1409 UTC on the 14th day of the month.
Coding for the Amended TAF
| Description of Amended TAF in the sample above... | Example |
| The date/time in the WMO header line is the same date/time as the original scheduled TAF. | 141100 |
| The contraction "AAA" indicates this is the first amendment for the KMFL TAF. The last "A" in the string indicates this is the first amendment. A second issued amendment would be indicated by the string "AAB", the third amendment by the string "AAC" and so forth. | AAA |
| Identifies this is an amended TAF. | TAF AMD |
| This is the amended TAF issuance time. It was issued at 1409 UTC on the 14th day of the month. | 141409Z |
| valid period - The TAF is valid from 1400 UTC on the 14th to 1200 UTC on the 15th day of the month. The new valid time "1414" is based on the issuance time. An issuance time of H+00 to H+29, we use the current UTC hour to denote the beginning valid time. An issuance time of H+30 to H+59 would use the next UTC hour. | 1414/1512 |