There are two types of aerodrome forecast, a TAF and a TREND.
A TAF is an aerodrome forecast provided for a specific aerodrome and presented in code. Cloud base is forecast in feet above aerodrome level and wind direction is in degrees true.
An aerodrome forecast applies only to an area within 8 km of the centre of the aerodrome. Practically, this means the cloud and visibility information contained in the forecast is only applicable to the aerodrome and a small area around it. It should not be used for assessing visibility in the wider geographical area.
The TEMPO when used in a TAF is used to describe expected temporary fluctuations in the meteorological conditions, that reach or pass specified threshold values and last for a period of less than one hour in each instance. Such fluctuations take place sufficiently infrequently for the prevailing conditions to remain those originally forecast. We have animated a typical TEMPO to show what it would look like.
A TREND is a forecast, valid for two hours, attached to the end of a METAR (NZWP and NZOH only) and in METAR AUTO for NZAA, NZWN and NZCH only. It states any significant changes from those described in the METAR.
While the TREND is valid it supersedes the aerodrome TAF.