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Aerodrome forecasts and reports

TAF (aerodrome forecast) format AIP GEN 3.5

METAR/SPECI (aerodrome weather report) format

Aerodrome weather and forecast decode AIP GEN 3.5

Identifier

METAR is used to identify routine observations (hourly or half-hourly) when conditions are above specified levels. SPECI is used to identify special observations, that is, observations when conditions are below specified criteria, or when there have been significant changes since the previous report. SPECI is also used to identify observations reported 10 minutes following an improvement to above SPECI conditions.

TTF METAR or TTF SPECI is used to identify METAR or SPECI to which a trend forecast is appended. The use of this identifier is restricted to those locations that issue Trend Forecasts.

TAF, TAF AMD, TAF COR, TAF… CNL, TAF… NIL and PROV TAF are used to identify Aerodrome Forecast, Amended Aerodrome Forecast, Corrected Aerodrome Forecast, Cancelled Aerodrome Forecast, Nil Aerodrome Forecast and Provisional Aerodrome Forecast respectively.

For message formats, see AIP GEN sections 14 (METAR/SPECI), 15 (TAF) and 17 (TTF).

Location

The location is indicated by the ICAO location indicator, the place name, or the approved abbreviation.

Origination time

The origination date/time of TAF and METAR/SPECI is given in UTC using a six figure group followed by the code Z (for UTC).

Validity period

The validity period of a TAF is given in UTC in the format ddhh/ddhh, where ddhh is the day of month and hour, for example: 0100/0206 is a validity period from 00 UTC on the 1st until 0600 UTC on the 2nd.

Auto

This group will be included when the METAR/SPECI contains only automated observations, which may include visibility, present weather, and cloud.

When the Automatic Weather Station (AWS) includes sensors for horizontal visibility, present weather and cloud, the AUTO report will include the parameters from these sensors in the body of the message (where previously only manually observed visibility, present weather and cloud data were included).

Wind AIP GEN 3.5

Wind direction is rounded to the nearest 10 degrees and is given in three figures relating to true north. Wind speeds are given in two figures. When the wind is calm, the group is encoded as 00000KT.

A variable wind direction is given as VRB and is used when the reporting or forecasting of a mean wind direction is not possible, such as in the following conditions:

  • light winds (3 kt or less) or
  • when forecasting a single direction is not possible, for example: with a tropical cyclone, or with the passage of a thunderstorm, in which case the forecast wind might be VRB60KT.

Maximum wind speed is given only when it is 10 kt or more greater than the mean wind speed. It is indicated by the letter G which is followed by the maximum wind speed, for example: 280°, mean speed 20 kt, maximum speed 35 kt, is given as 28020G35KT.

At some aerodromes, an additional wind group will be given in METAR/SPECI when the direction varies by 60° or more during the sampling period (normally ten minutes). The group gives the extreme range of directions in clockwise order, for example: 360V090.

Visibility

In TAF, the prevailing visibility (the greatest visibility covering more than half the aerodrome) is always given.

In METAR/SPECI, if the visibility is not the same in different directions and:

  • the minimum visibility is the prevailing visibility or
  • the visibility is fluctuating rapidly, then

the minimum visibility is the only information provided. When the minimum visibility is not the prevailing visibility and the minimum visibility is less than 5000M, both the prevailing visibility and the minimum visibility will be given. In this case the prevailing visibility is reported first followed by the minimum visibility including an indicator to show the general direction of the minimum visibility in relation to the observing point (the meteorological station), e.g. the visibility groups 9000 0600N indicate a prevailing visibility of 9000M and a minimum visibility of 600M to the north.

A visibility of 10 km or more is given by 9999.

Automatic visibility information

A report from an AWS with a visibility sensor will include data from this sensor in the body of the report if the report is fully automated (in which case the abbreviation AUTO is also included in the message).

Fully automated AWS may issue special reports (SPECI) for visibility using data from visibility sensors.

Runway visual range (RVR)

RVR may be reported in SPECI messages from aerodromes with RVR instrumentation.

RVR at the runway’s touchdown zone may be reported in SPECI messages from aerodromes with RVR instrumentation. It will be reported in the format RDD/VVVVi or RDD/VVVVVVVVVi where:

  • R and V are fixed indicators;
  • DD gives the runway number, for example 36;
  • VVVV gives the RVR value and
  • i gives the tendency (either U, D or N for up, down or nil).

When RDD/VVVVi is reported, VVVV is the average—normally over 10 minutes.

RDD/VVVVVVVVV is reported when the RVR has varied significantly during the averaging period. The group gives the one-minute mean minimum RVR value followed by V followed by the one-minute mean maximum RVR value during the averaging period, for example: R16/0500V1100.

Present weather

Present weather is given using the codes listed on page 2.36

Appropriate intensity indicators and letter abbreviations will be combined in groups of two to nine characters to indicate present weather at, or in the vicinity of, the aerodrome. If more than one form of precipitation is observed, the appropriate letter abbreviations shall be combined in a single group with the first being the dominant type of precipitation. In such a group, the intensity shall refer to the total precipitation.

Up to three groups may be given.

The intensity of precipitation, blowing dust, sand or snow, dust storm and sand storm will be indicated by the prefix – for light, + for heavy, and no prefix for moderate.

The qualifier VC will be used to report certain significant weather phenomena in the vicinity (between approximately 8–16 km of the aerodrome reference point) of the aerodrome.

Automatic present weather information

A report from an AWS with a present weather sensor will include data from this sensor in the body of the report if the report is fully automated, in which case the abbreviation AUTO is also included in the message (AIP GEN 3.5).

Cloud

Cloud height is reported in hundreds of feet using three figures, for example: 700 ft is reported as 007.

Cloud amount is given using the following abbreviations listed on page 2.36.

In a weather report, nil cloud is reported as SKC (sky clear). In a weather forecast, cloud information is not included if the sky is clear.

Cloud information is given from the lowest to the highest layer or mass in accordance with the following criteria:

  • the lowest layer or mass, regardless of amount
  • the next layer or mass, covering more than 2 OKTAS
  • the next higher layer or mass, covering more than 4 OKTAS and
  • cumulonimbus and/or towering cumulus clouds whenever observed or forecast and not reported in one of the groups above.

Type of cloud is identified only for cumulonimbus and towering cumulus observed at or near the aerodrome. These will be given as CB and TCU respectively. When an individual layer or mass of cloud is composed of cumulonimbus and towering cumulus with a common cloud base, the type of cloud is reported as cumulonimbus only, and the amount shall be reported as the sum of the CB and TCU amounts.

Whenever cumulonimbus cloud is forecast, the degree of associated thunderstorm activity or probability of occurrence is included.

A clear sky will be indicated in a report by SKC. When the sky is obscured, the cloud group is omitted and vertical visibility may be given in the format VVhhh, where hhh is the vertical visibility in hundreds of feet. When information on vertical visibility is not available, hhh may be given as ///, indicating that the sky is obscured but information on the vertical visibility is not available.

CAVOK

CAVOK is included in reports (from staffed stations only) or forecasts when the following conditions are observed, or forecast to occur, simultaneously:

  • visibility of 10 km or more;
  • nil significant cloud, that is, no cloud below 5000 ft or below the highest 25 nm minimum sector altitude, whichever is greater, and no cumulonimbus or towering cumulus at any height and
  • nil significant weather, that is, none of the weather listed on page 2.37.

When the term CAVOK is given, the elements visibility, weather and cloud will not be given.

In METAR/SPECI, whenever a total of BKN or more of low or middle cloud cover is at or above 5000 ft, and CAVOK has been used, the cloud amount and base may be given as a remark after the RMK indicator.

Automatic weather stations with cloud information

A report from an AWS with a cloud sensor will include data from this sensor in the body of the report if the report is fully automated (in which case the abbreviation AUTO is also included in the message). The data will be in the same form as manual reports except that:

  • NCD will be reported if no cloud is detected and
  • there will be no indication of cumulonimbus or towering cumulus.

AWS may issue special reports (SPECI) for cloud using data from cloud sensors.

Significant variation

Aerodrome forecasts will include significant changes or variations (indicated by FM, BECMG, INTER and TEMPO) to the previously given conditions when the relevant criteria are met. These relate to improvements as well as deteriorations.

The variation groups TEMPO and INTER are used to indicate significant variations of a temporary or intermittent nature. The change groups FM and BECMG are used to specify changes that are more lasting in nature. The indicators are the beginning of a self-contained forecast.

When thunderstorms or reduced visibility due to fog, mist, dust, smoke or sand is forecast, but the probability is assessed at between 30 per cent and 40 per cent, the terms PROB30 or PROB40 are used. INTER or TEMPO may also be used with a PROB for thunderstorms. If greater than, or equal to, 50 per cent probability is forecast, reference is made to the phenomenon in the forecast itself and not by the addition of a PROB statement.

The terms NSW (nil significant weather), and NSC may be included following FM or BECMG to indicate significant improvements expected.

If a TAF or TTF includes a forecast of turbulence, its commencement will be indicated by the abbreviation FM, and its cessation within the forecast coverage will be indicated by the abbreviation TILL. Start and finish times are given in the format ddhhmm (day of month, hour, minute). Turbulence associated with CB and TCU clouds is not included in forecast as it is implied.

Temperature

Aerodrome weather reports contain both air temperature and dewpoint.

Up to four forecast values of air temperature are given, for the times HH, HH+3 hours, HH+6 hours and HH+9 hours, where HH is the time of commencement of the TAF validity period. Users should use linear interpolation to determine the forecast value between these points.

The temperature forecasts are prefixed by the letter T. Negative values are indicated by the letter M before the numeral.

QNH

QNH is given in whole hectopascals using four figures.

Observed intermediate values are rounded down, for example: 1001.9 is reported as 1001.

QNH is always given, prefixed by the letter Q, for example: Q0999.

Up to four forecast values of QNH are given, for the times HH, HH+3 hours, HH+6 hours and HH+9 hours, where HH is the time of commencement of the TAF validity period. Users should use linear interpolation to determine the forecast value between these points. The QNH forecasts are prefixed by the letter Q.

Supplementary information

In METAR/SPECI, supplementary information is used to report the following:

  • recent weather (RE) of operational significance and
  • wind shear (WS) information on a take-off or landing runway.

Remarks section

Rainfall

The remarks section of the report will include rainfall recorded by an automatic rain gauge. The information is in the form RF##.#/###.# where the first three digits after the indicator RF will report the rainfall recorded in the 10 minutes prior to the observation time, and the next four digits report the total rainfall recorded since 0900 local time. Both amounts are expressed in millimetres to the nearest 0.2 mm.

Plain language

Any other significant weather conditions (for example an approaching front or visible bushfires) are appended in plain language.

Elements not available

A report from a fully automated AWS that does not include information from sensors for visibility, weather, or cloud will report ////, // or ////// respectively in lieu of these parameters.

Terminal Area Forecast (TAF) examples

TAF YCOM 070635Z 0708/0720 18015KT 9999 FEW005 BKN020

TEMPO 0710/0714 2000 -SHSN BKN005 SCT020

RMK T 03 00 M02 M04 Q 1008 1007 1006 1006

TAF YSSY 020435Z 0206/0312 31005KT CAVOK

FM021400 16015KT 8000 SHRA BKN008 SCT030

FM022300 23010KT 9999 NSW SCT030

RMKT 25 21 18 15 Q 1012 1013 1014 1014/span>

TAF YSCB 270448Z 2706/2806 33015G28KT 3000 +RABKN010 OVC100

FM271400 16015KT 8000 SHRA FEW010 SCT040 SCT100

INTER 2710/2714 1000 +TSRA BKN005 SCT040CB

RMK FM270800 MOD TURB BLW 5000 ft TILL271300

T 14 13 13 11 Q 1016 1015 1013 1016

Aerodrome weather report examples

SPECI YMML 092000Z 22012KT 170V260 6000 SHRA SCT035TCU 31/20 Q1020 RETS RMK RF02.0/004.0

SPECI YBCS 221745Z 23014G29KT 6000 1200NE TSRA FEW040CB BKN100 26/22 Q1003 RMK RF04.0/004.0

SPECI YSSY 271915Z VRB01KT 3000 VCFG FEW030 18/17 Q1018 RMK RF00.0/000.0

METAR YMOR 100400Z 06013KT 9000 VV/// 31/08 Q1010 RMK RF00.0/000.0 SKY OBS DUE BUSH FIRE SMOKE

SPECI YSCB 141400Z AUTO 20008KT 9000 // BKN016 14/11 Q1001 RMK RF00.0/000.0

SPECI YMAV 240215Z AUTO 36018G28KT 9999 // NCD 31/10 Q1014 RMK RF00.0/000.0

METAR YSBK 241700Z AUTO 15002KT 0900 // ////// 04/04 Q1020 RMK RF00.0/000.0 CLD: SKY MAY BE OBSC

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