How to Interpret Aviation Weather Information

Contents of this page:

Height References
Temperature and Pressure Values
Date and Time
Area of Applicability
Meteorological Terminology
Codes and Abbreviations used in METAR,SPECI and TAF
Forecast Terminology

Height References

Aviation Weather Product	Height Reference
TAF METAR/SPECI TREND VOLMET Takeoff & landing reports SPAR ATIS	100s of feet above aerodrome level
ARFOR	Feet above mean sea level
SIGMET	Feet above mean sea level up to 10,000 ft and flight levels at and above FL100
ROFOR	Flight levels
SIGWX charts	Flight levels
WIND/TEMP charts	Flight levels
SATPIX	Flight levels

Temperature and Pressure Values

Weather Element	Unit
Temperature	Degrees Celsius
Pressure	Hectopascals (hPa)

Date and Time

Weather Product	Unit
All	UTC

Area of Applicability

Aviation Weather Product	Area of Applicability
TAF	Within 8 km radius of the aerodrome reference point.
METAR/SPECI	Within 8 km radius of the aerodrome reference point. When the term Vicinity (VC) is used this applies to the area within an 8 to 16 km radius of the aerodrome reference point.
ARFOR	Within the named area, eg, TM (Tamaki). Refer to Weather Information for Your Flight. Coastal forecast areas extend 15 NM seaward from the coastline. ARFORs Map
SIGMET	New Zealand (NZZC) and Auckland Oceanic (NZZO) FIRs.
ROFOR	Specific route(s) and levels indicated in a ROFOR.
HI-Level SIGWX charts	Within specific geographical areas and for the airspace between FL250 and FL630.
Mid-Level SIGWX charts	Within specific geographical areas and for the airspace between FL100 and FL250.
WIND/TEMP charts	Specific geographical areas and Flight Level noted on the charts.

Meteorological Terminology

Wind
	Product	Terminology
Speed	METAR SPECI TREND TAF VOLMET ARFOR Take-off & landing reports SPAR ATIS	Knots, with gusts indicated where they exceed the mean wind speed by 10 knots or more. Gust information follows the mean wind speed separated by the letter G, eg, 24015G30KT Calm is indicated by 00000KT
Direction	METAR SPECI TREND TAF VOLMET ARFOR	Degrees true VRB indicates variable, eg, VRB02KT
Direction	Takeoff & landing reports SPAR ATIS	Degrees magnetic
Direction Variability	METAR SPECI	When the direction varies by 60 degrees or more, the extreme directions are given, separated by the letter V, eg, 260V330

Visibility (for Auckland, Wellington and Christchurch aerodromes only)
Prevailing Visibility is defined as the maximum visibility covering at least half of the total horizon (note: the sections of the horizon do not have to be adjoining).	METAR SPECI	Prevailing visibility is reported in metres up to a maximum of 9999 metres. Prevailing visibilities of 10km or greater are reported as 9999. Where there is a marked variation in the visibility, the minimum visibility is added with a direction given e.g. 7000 1200SW where the prevailing visibility is 7000 metres).
	TREND TAF VOLMET	Visibility is forecast in metres up to a maximum of 9999 metres. Visibilities of 10 km or greater are forecast as 9999.
	Takeoff & landing reports SPARs ATIS	Reported in metres when the visibility is less than 5000 metres, eg 3000 m. Visibilities of 5000 metres or more are reported in kilometres, eg 5 km.
Visibility (for domestic aerodromes other than NZAA, NZWN and NZCH, and for ARFORs)
Prevailing Visibility is defined as the maximum visibility covering at least half of the total horizon (note: the sections of the horizon do not have to be adjoining).	METAR SPECI	Up to 9999 metres, prevailing visibility is reported in metres, eg 3000. Prevailing visibility above 9999 metres is reported in kilometres, eg 10 km, 20 km, etc. Where there is a marked variation in the visibility, the minimum visibility is added with a direction given, eg 7000 1200SW (where the prevailing visibility is 7000 metres).
	TREND TAF ARFOR	Up to 9999 metres, visibility is forecast in metres, eg 7000. Above 9999 metres, visibility is forecast in kilometres, eg 20 km.
	Takeoff & landing reports SPARs ATIS	Reported in metres when the visibility is less than 5000 metres, eg 3000 m. Visibilities of 5000 metres or more are reported in kilometres, eg 5 km.

Runway Visual Range (only reported at Auckland aerodrome)
Instrumented Runway Visual Range (IRVR) equipment has been installed at Auckland International Airport on RWY 05R/23L. The equipment consists of three transmissometers located adjacent to the Touchdown zone, the runway Mid-point, and the runway Stop-end.
	Product	Terminology
RVR	METAR SPECI	Reported when Runway Visual Range (RVR) or visibility is less than 1500 m. Is reported for the touchdown zone of the runway(s) in use. The runway designator is reported followed by the RVR, eg, R05/1400. If the RVR during the 10 minutes before the observation time shows a distinct upward or downward tendency, U for upward or D for downward is added. When it is not possible to determine the tendency N is used. When the RVR exceeds 2000 m, it is reported as P2000 and when it is less than 50 m it is reported as M0050.
RVR	SPAR ATIS	RVR is broadcast on the ATIS, and included in SPARs issued by Auckland Tower, and is advised directly to the pilot by TOWER. The Touchdown zone RVR will be reported whenever the observed value is less than 1500 m. The Mid-point and Stop-end RVR will only be reported when the observed value is: (a) Less than the Touchdown zone value; or (b) Less than 600 m.

Cloud
	Product	Cloud Type or amount	Code
Cloud Type	TAF TREND VOLMET	Cumulonimbus	CB
	METAR SPECI Takeoff & landing reports SPAR ATIS	Cumulonimbus Towering Cumulus	CB TCU
	ARFOR	Cumulonimbus Towering Cumulus Altostratus Altocumulus Nimbostratus Stratocumulus Stratus	CB TCU AS AC NS SC ST
Note: When Cumulonimbus cloud (CB) is included in meteorological information (observations, forecasts and all weather charts), this implies that there may be associated thunderstorms and the occurrence of severe icing, turbulence, and hail.
Cloud Amount	METAR SPECI TAF TREND VOLMET ARFOR Takeoff & landing reports SPAR ATIS	Sky clear (no cloud at all) 1 - 2 oktas (few) 3 - 4 oktas (Scattered) 5 - 7 oktas (Broken) 8 oktas (Overcast)	SKC FEW SCT BKN OVC
Note: When the sky is obscured, or forecast to be obscured (eg because of fog), the cloud group will be shown as VV/// (vertical visibility unavailable).
Additional METAR/SPECI Terminology
	Product	Terminology	Code
	METAR SPECI	Corrections to reports are indicated using the code letters, eg, SPECI COR. This implies that the text of the SPECI and/or the text of an appended TREND has been corrected.	COR

Codes and Abbreviations used in METAR,SPECI and TAF

Forecast Terminology

Forecast Terminology
Product	Terminology	Meaning/Description
TAF	AMD	Amended: as in TAF AMD
	COR	Corrected: as in TAF COR
	BECMG Example BECMG 1522/1601	Used to describe changes where the meteorological conditions are expected to reach, or pass through, specified threshold values at a regular, or irregular, rate, and at an unspecified time within a period. In this example, the period of time concerned is 2200 on the 15th to 0100 UTC on the 16th.
	FM Example FM052230	Used when one set of prevailing weather conditions is expected to change significantly, and more or less completely, to a different set of conditions, with the change expected to occur at the time indicated. In this example, the time of the change is 2230 UTC on the 5th.
	TEMPO Example TEMPO 0602/0607	Used to describe expected frequent, or infrequent, temporary fluctuations in the meteorological conditions, which 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. In this example, the temporary fluctuations are expected to occur between 0200 and 0700 UTC on the 6th.
	PROB Example 1: PROB30 1117/1121 0500 FG Example 2: PROB40 TEMPO 1402/1406 3000 +TSRA BKN018CB	Used to indicate the probability of the occurrence of an alternative forecast element over a specified time period. This example indicates that there is a 30% chance of visibility reducing to 500 m in fog between 1700 and 2100 UTC on the 11th. This example indicates that there is a 40% chance that temporarily between 0200 and 0600 UTC on the 14th, the visibility will reduce to 3000 m in heavy thunder-storms and rain, with broken Cumulonimbus cloud at 1800 ft above aerodrome level.
TREND	NOSIG	No Significant Change to the conditions reported in the METAR or SPECI. Note: If the trend “NOSIG” is appended to aSPECI reporting poor visibility and/or low cloud, the conditions at that aerodrome are forecast not to change during the 2 hours following the issue time of the SPECI.
	BECMG Example 1 BECMG FM0500 Example 2 BECMG TL1800 Example 3 BECMG AT2130	Used to describe changes where the meteorological conditions are expected to reach or pass through specified threshold values at a regular or irregular rate, with such changes expected to occur throughout the 2-hour validity of the TREND. This example indicates that the changes are expected to occur from 0500 UTC. This example indicates that changes already occurring are expected to be complete by 1800 UTC. This example indicates that the change in conditions is expected to occur at 2130 UTC.
	TEMPO Example 1 TEMPO FM2300 Example 2 TEMPO TL0400	Used to describe expected frequent or infrequent temporary fluctuations in the meteorological conditions, which reach or pass specified threshold values, and last for a period of less than one hour in each instance. Such fluctuations are expected to occur during the 2 hours following the issue time of the METAR or SPECI, and to take place sufficiently infrequently for the prevailing conditions to remain those originally reported in the METAR or SPECI. As for TEMPO above, except that such temporary fluctuations are expected to commence occurring from 2300 UTC. As for TEMPO above, except that such temporary fluctuations are already occurring and are expected to cease from 0400 UTC..
TAF TREND ARFOR	NSW	Nil Significant Weather
ARFOR	FZL	Freezing Level in feet above mean sea level
	WX	Forecast weather
	TURB	Turbulence
	ICE	Icing
	FREQ	Frequent
	OCNL	Occasional
	PS MS	Plus eg, PS06 is plus 6 degrees Celsius Minus eg, MS03 is minus 3 degrees Celsius

AIP New Zealand Table GEN 3.5-1 Meteorological Terminology (Additional terminology applicable only to Auckland, Wellington, and Christchurch aerodromes)