TEMPO in a METAR
Trends in a METAR may only be included if it is written by a forecaster and not an observer. There may be a trend on the way, but it may not be reported as there may just be an observer on duty. When I was taught to read them many years ago, we were told that if there is no trend statement, then the METAR should be considered valid for one hour only.
The part I dont understand is if a METAR which is a report issued every 30 or 60 mins, is issued with a TTF, which in AUS is valid for 3 hours, what happens to the validity of that same TTF when the metar is updated in 30 mins time?
Trends in a METAR may only be included... that if there is no trend statement, then the METAR should be considered valid for one hour only.