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, METAR AUTO, SPECI and TAF
Forecast Terminology
Known Ice and Known Icing Conditions - Definition

Height References

Aviation Weather Product Height Reference

TAF
METAR/SPECI
METAR/AUTO                                            TREND
VOLMET
Takeoff & landing reports
ATIS

100s of feet above aerodrome level

ARFOR Feet above mean sea level
SIGMET
VAA
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

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Temperature and Pressure Values

Weather Element Unit
Temperature Degrees Celsius
Pressure Hectopascals (hPa)

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Date and Time

Weather Product Unit
All UTC

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Area of Applicability

Aviation Weather Product Area of Applicability
TAF Within 8 km radius of the aerodrome reference point. However, for cloud the area is within 16 km of the aerodrome reference point.
METAR/SPECI
METAR/AUTO
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
VAA
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.

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Meteorological Terminology

Wind
  Product Terminology
Speed

METAR
SPECI
METAR AUTO TREND
TAF
VOLMET
ARFOR
Take-off & landing reports
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
METAR AUTO TREND
TAF
VOLMET
ARFOR

Degrees true

VRB indicates variable, eg, VRB02KT

Takeoff & landing reports
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 AUTO Prevailing visibility is reported in metres up to a maximum of 9999 metres. Prevailing visibilities of 10km or greater are reported as 9999.
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
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*
METAR AUTO
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
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
AUTO

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 1500 m, it is reported as P1500 and when it is less than 50 m it is reported as M0050.

RVR ATIS

RVR is broadcast on the ATIS 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
Towering Cumulus
CB
TCU
  METAR
SPECI
Takeoff & landing reports
METAR AUTO
ATIS
Cumulonimbus
Towering Cumulus
CB*
TCU*

* Not included in METAR AUTO

  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
METAR AUTO
TAF
TREND
VOLMET
ARFOR
Takeoff & landing reports
ATIS

Sky clear
No significant cloud
1 - 2 oktas (Few)
3 - 4 oktas (Scattered)
5 - 7 oktas (Broken)
8 oktas (Overcast)

SKC1
NSC2
FEW
SCT
BKN
OVC

Notes:
1. Not used in TAF for NZAA, NZWN and NZCH
2. Only used in TAF for NZAA, NZWN and NZCH
3.  When the sky is obscured, or forecast to be obscured (eg, because of fog), the cloud group will be shown as V V /// (vertical visibility unavailable).
Additional METAR/METAR AUTO/SPECI Terminology
  Product Terminology Code
METAR
METAR AUTO
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.

No directional variations. Note that this is not used in METAR AUTO reports for NZAA, NZWN and NZCH.

COR





NDV

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Codes and Abbreviations used in METAR, METAR AUTO, SPECI and TAF

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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

Known Ice and Known Icing Conditions - Definition

Terminology Definition
Known Ice/Icing Known ice/icing is the situation where ice formation on an aircraft is actually detected or observed.
Known Icing Conditions Known icing conditions are those where a pilot would expect a substantial likelihood of ice formation on an aircraft based on all the information available to a pilot, eg, weather reports, aircraft reports, forecasts and warnings.

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