METAR

METAR

The word METAR comes from the French phrase "message d’observation météorologique régulière pour l’aviation". It is thought to be a contraction of the French words MÉTéorologique ("Weather") Aviation Régulière ("Routine"). A METAR is a codified observation message indicating airfield weather conditions observed at a given time. Such a message is established every hour, even sometimes every 30 minutes or shorter due to fast and heavy weather changes which affects the traffic flow.

Sample:

LOWW 011220Z 33007KT 280V020 3000 R34/1500 +RASH FEW040 BKN058TCU 16/07 Q1014 RETS WS RWY34
34231091 BECMG -SHRA SCT030CB

Detailed explanation

1.) Location Identifier: LOWW
The four-letter ICAO code of the observing location.

2.) Day of Month/Zulu Time: 011220Z

3.) Wind: 33007KT
Wind direction (true heading), rounded to the nearest ten degrees and always expressed as three digits. Direction can be given as VRB if wind direction is variable and wind speed is at most 3 knots.
plus
average wind speed of last 10 minutes in knots.
or
maximum gust wind speed in knots.
If it is calm, the wind is given as 00000KT.

4.) Variable Wind Direction: 280V020
This field is used if the total variation of wind direction during the last 10 minutes is 60 degrees or more and wind speed is more than 3 knots. The direction extrema are given in clockwise order

5.) Horizontal Visibility: 3000
Usually, only the minimum visibility is reported. If the minimum is less than 1500m and the maximum is over 5000m, the maximum visibility and its direction are indicated by a second visibility group following the minimum visibility.

6.) RVR Runway Visual Range: R34/1500
Runway designator and runway visibility in meters.

7.) Significant Weather: +RASH
Intensity is expressed by: + = heavy, - = light, nothing = moderate
Proximity is described by: VC = ViCinity (within 8km)

  BC = Banc - fog bench
 BL = Blowing
 DR = Drifting
 FZ = Freezing
 MI = Mince - thin fog layer
 SH = Shower
 TS = Thunderstorm
 DZ = Drizzle
 GR = Grêle - hail (diameter > 5mm)
 GS = Grêsil - hail (diameter < 5mm)
 IC = Ice Crystal
 PE = Ice Pellets
 RA = Rain
 SG = Snow Grains
 SN = Snow
 BR = Brume - mist (vis 1000 to 3000m)
 DU = Dust
 FG = Fog (vis < 1000m)
 FU = Fumée - smoke (vis < 3000m)
 HZ = Haze
 SA = Sand
 VA = Vulcanic Ashes
 DS = Dust Storm
 FC = Funnel Clouds
 PO = Dust Spins
 SQ = Squall
 SS = Sand Storm

8.) Clouds and Ceiling: FEW040 BKN058TCU

Cloud coverage:

  FEW = few - 1 to 2 octas
 SCT = scattered - 3 to 4 octas
 BKN = broken - 5 to 7 octas
 OVC = overcast - 8 octas

Cloud types:

  CB = cumulunimbus
 TCU = towering cumuli or cumulus congestus

Also common:

  SKC = Sky Clear (no clouds)
 OVC/// = clouds covering the sky and which base is below aerodrome level
 VV/// = sky not visible
 VV002 = vertical visibility is 200ft
 CAVOK = ceiling and visibility is OK (vis > 10km and SKC)

9.) Temperature and Dew Point: 16/07
The difference between temperature and dew pont is called "spread", the smaller the spread the higher the risk of precipitation.

10.) Pressure, QNH (altimeter setting): Q1014
QNH = 1014 hPa (hectopascals - 1hPa = 1mb - millibar)

11.) Recent Weather: RETS
Recent Thunderstorm
Also:

  RERA = recent rain
 RESN = recent snow
 NOSIG = no significant change

12.) Wind Shear: WS RWY34
Also:

  WS TKOF RWY 16 = windshear when taking of runway 16
 WS LDG RWY 34 = windshear when landing at runway 34
 WS ALL RWYS = windshear all runways

13.) Runway Status: 34231091
34 = runway 34
2 = wet
3 = covering 26 to 50% of runway surface
10 = 10mm thick
91 = braking action poor

Explaination:
1st and 2nd figure = runway designator
3rd figure = type of deposit on the runway

  0 = runway clean and dry
 1 = damp
 2 = wet
 3 = frost
 4 = snow
 5 = wet snow
 6 = slush
 7 = ice
 8 = compacted snow
 9 = snow drift
 / = unknown, removal in progress

4th figure = percentage of runway contamination

  1 = less than 10%
 2 = 11 to 25%
 3 = 26 to 50%
 4 = 51 to 100%
 / = unknown, removal in progress

5th and 6th figure = deposit thickness

  01 to 90 = millimeters
 92 = 10cm
 93 = 15cm
 94 = 20cm
 95 = 25cm
 96 = 30cm
 97 = 35cm
 98 = 40cm
 99 = unknown
 // = unable to measure

7th and 8th figure = braking action

  01 to 90 = coefficient 0.01 to 0.90
 or
 91 = poor
 92 = medium to poor
 93 = medium
 94 = medium to good
 95 = good
 99 = uncertain
 // = unknown

14.) Trend: BECMG -SHRA SCT030CB
Consists of following keywords and other METAR components:

  BECMG: becoming
 TEMPO: temporarily
 NOSIG: no significant change expected within 2 hours
 AT: at
 FM: from
 TL: until

15.) Remarks:
RMK followed by METAR components and miscellaneous abbreviations.

Links

• TAF
• Detailed Metar Guide (.pdf)