An aerodrome report applies only to an area within 8 km of the centre of the aerodrome, except when VC is used, when it refers to the area between 8 and 16 km from the aerodrome.
If you are standing on the earth’s surface and can see the horizon, then the horizon will be approximately 12 km away. Therefore, observations made from the surface cannot account for low cloud or fog any further away than 12 to 16 km.
This is one of the reasons reports and forecasts cannot be accurate any further away than this.
A METAR is a routine meteorological report, compiled manually, provided for a specific aerodrome, and presented in code. Cloud base is reported in feet above aerodrome level and wind direction in degrees true.
The only aerodromes that still issue manual METAR are Whenuapai, Ohakea and Milford Sound.
A METAR AUTO is a routine meteorological report provided by an automatic weather station for a specific aerodrome, also presented in code. METAR AUTO are issued every 30 minutes (on the hour and half-hour) day and night.
The visibility figure in a METAR AUTO will have ‘NDV’ added to it. This indicates the visibility reported is the visibility at the measuring station, and it cannot be assumed to be the same for the entire area.
METAR AUTO do not include cloud type. They do include present weather at the aerodrome, but cannot report weather in the vicinity of the aerodrome (between 8 and 16 kilometres away). However, if lightning is detected in the vicinity of the aerodrome then VCTS will be included.
A SPECI is effectively a METAR issued outside of the routine issue time of a METAR. The presence of a SPECI should alert you to changing conditions — generally worsening. But do not rely on worsening conditions automatically leading to a SPECI — if the change coincides with a routine METAR issue time there will just be a new METAR and not a SPECI.
A TREND is a forecast, valid for two hours, attached to the end of the METAR stating any significant changes from those described in the METAR.
While the TREND is valid, it supersedes the aerodrome TAF.
The TREND forecast is added to the METAR by a MetService Forecaster and is only available for Auckland, Whenuapai, Ohakea, Wellington, and Christchurch aerodromes. The TREND forecast is required at Auckland, Wellington and Christchurch to fulfil international obligations, and the RNZAF request them for Whenuapai and Ohakea.
The ATIS is a continuous plain language broadcast of the current conditions at an aerodrome, on a discrete frequency.
ATIS are issued by ATS at controlled aerodromes. Cloud base is reported in feet above aerodrome level and wind direction in degrees magnetic.
A Basic Weather Report is a verbal weather report, or comment, on present weather conditions intended for aviation use. The person providing a BWR is required to have been trained to provide them. The holder of any pilot licence, or similar qualification, is considered appropriately trained for this.