Trend type forecasts
Trend Type Forecast (TTF)
At major aerodromes, a statement of trend, valid for three hours from the time of the observation, is appended to the observation (AIP GEN 3.5). TTF service is provided for the following locations:
The TTF relates to weather conditions expected to affect the aerodrome of origin for the validity period of the forecast. This period is three hours unless, if the TTF service is not 24 hours, the TTF commencement falls within the last three hours of the service cessation. If the TTF validity is reduced to less than three hours, this will be indicated in the remarks section (AIP GEN 3.5), for example: Use TAF for arrival after 0800Z.
The decode of the TTF is as per that for the METAR/SPECI, except there
is a statement of trend appended to the forecast. This may contain the following (AIP GEN 3.5):
- NOSIG is used to indicate that no significant changes to the wind, \ visibility, weather and cloud, as reported in the METAR/SPECI, are expected to occur during the validity period of the TTF
- FM (time) indicates that significant changes to a new set of mean conditions, from those previously given, are expected to occur at the specified time and to persist until the end of the validity period of the TTF, or until new mean conditions are given/li>
- INTER (periods less than 30 minutes) and TEMPO (periods of between 30 minutes and 60 minutes) are given as INTER and TEMPO (time2/time3) – in this case, intermittent or temporary variations are expected to commence at (time2) and to end at (time3)
- Turbulence associated with CB and TCU clouds is not included in the forecast as it is implied. TILL (time) is used if the turbulence is expected to cease before the end validity period of the TREND.
The TTF supersedes the TAF for its validity period and is the current forecast for pilots of aircraft whose arrival time falls within the validity period. Note that PROB is not used in TTF, but it is included in a TAF. For aerodromes where the TTF is not a 24-hour service, the TAF will become the valid forecast from the time indicated in the remarks section of the TTF. For example:
Use TAF for arrival after 0800Z.
Where applicable, TTF replaces TAF and present weather in VOLMET broadcasts.
Trend Type Forecast (ttf) examples AIP GEN 3.5
TTF SPECI YPAD 012200Z 00000KT 5000 DZ OVC005 14/14 Q1025 RMK RF00.4/000.4
FM2200 00000KT 9999 NSW BKN008
FM2300 03005KT 9999 NSW SCT020
TTF SPECI YMML 100200Z 05008KT 4000 DZ BKN005 OVC100 16/15 Q1017 RMK RF00.2/000.2 NOSIG
TTF METAR YPPH 120500Z 36015KT CAVOK 32/08 Q1014 RMK RF00.0/000.0
FM0630 28025KT 9999 NSW BKN030
INTER 0530/0730 5000 SHRA BKN008
TTF METAR YBTL 220730Z 35006KT 9999 FEW050TCU 31/21 Q1005 RMK
RF00.0/000.0 DISTANT THUNDER NOSIG
TTF SPECI YBTL 240800Z 03010KT 4000 TSRA BKN030CB SCT120 27/24 Q1008 RMK RF00.0/000.0
FM0830 03005KT 9999 SHRA BKN035
INTER 0830/1100 4000 TSRA SCT010 SCT030CB
TTF METAR YSCB 140600Z 20008KT CAVOK 14/11 Q1001 RMK RF00.0/000.0 NOSIG
USE TAF FOR ARRIVALS AFTER 0800Z