METAR Weather Reports Explained

METAR means Aviation Routine Weather Report; thought to be a contraction of the French words MÉTéorologique (= "Weather"), Aviation, Régulière (= "Routine"), it is a format for reporting codified weather information (it stems from the time of morse code use, hence the codification).

A METAR weather report is the report of a surface observation and used by civilian and military pilots in fulfillment of a part of a pre-flight weather briefing, but it is also used by meteorologists (who use aggregated METAR information to assist in weather forecasting).

Raw METAR is the most popular format in the world for the transmission of weather data. It is highly standardized through International Civil Aviation Organization (ICAO), which allows it to be understood throughout most of the world (here you can search your local METAR, status: Current, if you know the code of your airport: http://weather.noaa.gov/weather/metar.shtml (Should you not know it, google: Your Airport ICAO code, OR check the ICAO list of Aairports: http://en.wikipedia.org/wiki/List_of_airports_by_ICAO_code).

NOTE: The airport code refers to ICAO code of airports, not the ones you see on your baggage labels (IATA code). Example: "Palma de Mallorca" Airport in ICAO is "LEPA" (the "L" staning for Europe followed by a three digit identifier), not the IATA PMI you find on your luggage and which is the transport code.

The following is an example of a METAR from the Airport of Palma de Mallorca (it isn´t as it shows the US version of the METAR, which is different from the international one, I used it as example as I live here and you will find the US annotation very often. Details about the two diffferent annotations in the Appendix to this message, the following will all be following US rules).

Raw METAR: METAR LEPA 041656Z 19020G26KT 6SM -SHRA BKN070 12/08 A3016 RMK AO2

Basically, a METAR is divided (from left to right) into 10 sections which deal with different kind of information and have unique codes assigned to them: TYPE, ID, TIME, WIND, VIS(ability), WX (Weather and Obscurations, "wx" in pilot speak), SKY, T/TD (Temperature/Dew Point), ALT(itude) in barometric pressure scale, and optionally a REMARK

Above Raw Metar explained in detail (just click on any of the cells to go to the help dealing with that particular section, or simply scroll down to see all sections explained):

TYPE	ID	TIME	WIND	VIS	WX	SKY	T/TD	ALT	REMARK
METAR	LEPA	041656Z	19020G26KT	6SM	-SHRA	BKN070	12/08	A3016	RMK AO2

Additionally some links:

US definitions and METAR regulations: http://www.ofcm.gov/fmh-1/fmh1.htm

International definitions and METAR regulations (.pdf): http://www.wmo.int/pages/prog/www/WMOCodes/Manual/Volume-I-selection/Sel2.pdf

Hope you found this little lecture helpful,

Rattler

(Weather Station) ID: LEPA

In this example, L refers to a European Station and EPA is the three letter ICAO identifier for Palma International Airport. Other examples are - "K" designating a US station -:  KRFD (Rockford, IL), KAMA (Amarillo, TX) and KDEN (Denver, CO).

NOTE: The airport code refers to ICAO code of airports, not the ones you see on your baggage labels (IATA code: Palma would be PMI).

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Winds: 19020G26KT

- The 190 (the first three numbers) is the direction of the winds in degrees from 0 to 360 degrees (although you will never see 360 because after 350, it goes back to 0). Winds are always reported to a 10 degrees accuracy.

- The 20 (next two numbers) is the speed of the winds in knots.

- The G26 represents the wind gusts. In this case the gusts are 26 knots. This is just an example: Gusts will not always be on reported... there is criteria which must be met in order to report a gust. In general, unless it's really windy, you are not going to see gusts reported.

- The KT simply means knots. It will always be at the end. (1 knot = 1.852 km/h, for approximate conversion: KT x 2 - 10% = km/h)

- For winds speeds below 7 knots (12 km/h), you might see VRB005KT which means the wind direction is variable. This is the idea of "light and variable" that you might see in a forecast.

- For winds greater than 6 knots (11 km/h) you might see something like two groups in this section: 18015KT 150V210. This means that winds are from 180 degrees at 15 knots, but the direction is actually variable between 150 degrees and 210 degrees. In order to be variable above 6 knots, the winds must have at least a 60 degree variation in its direction. If a pilot sees something like this be sure he will be watching the wind sack on landing and have his hands on the throttles ready to go-around...

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Present Weather and Obscurations: -SHRA

(-) is the designator for light. Precipitation will either be light (-), moderate ( ), or heavy (+) based on certain criteria that must be met. This designator is always in the first position. For now, just understand that it is simply the intensity of the snow, rain, hail, sleet, or freezing rain.

- SH means showers and RA means rain. So the present weather is a light rain shower (some common excerpts of the full list below)



NOTE:

1. The weather groups shall be constructed by considering columns 1 to 5 in the table above in sequence, i.e. intensity, followed by description, followed by weather phenomena, and so on: e.g. heavy rain shower(s) with squalls is coded as +SHRASQ

2. To denote moderate intensity no entry or symbol is used.

3. Tornados and waterspouts shall be coded as +FC.

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Temperature and Dewpoint: 12/08

- 12 represents the air temperature in Celcius

- 08 represents the dewpoint in Celcius (Dew Point is the temperature where the water held in the air starts condensating, i.e. 100% humidity is reached)

- If the temperature or dewpoint falls below 0 there will be an "M" before it (i.e. 03/M02). "M" means minus.

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REMARKS: RMK AO2

- RMK simply means REMARKS and marks the end of the standard metar observation and the beginning of the remarks that are put in as necessay.

- A02 means that the site is automated and HAS a precipitation sensor. If it were AO1, there would be no precip sensor. This does not mean the site is un-manned. If there is an AUTO after the ID in the metar ob, then there is no observer.

NOTE: Again, this is only valid for US, internationally the remark section is simply appended without the "RMK".

The most common remarks display TRENDs, i.e. the development in the next 2 hours after METAR was published.

In Europe, e.g. NOSIG is an example of a TREND forecast which is appended to METARs at stations while a forecaster is on watch. NOSIG means that no significant change is expected to the reported conditions within the next 2 hours.

Here are only a few of the important and common remarks:

- Volcanic Eruptions are in plain english

- TORNADO, FUNNEL CLOUD, or WATERSPOUT

- Peak Wind (PK_WND)

- Wind Shift (WSHFT_time)

- BINOVC (Breaks in Overcast)
    BINOVC denotes a few, small clear patches in the overcast sky

- Tower or Surface Visibility (TWR_VIS SFC_VIS)

- CIG (Ceiling=Lowest BKN/OVC layer or height of VV)
    V (Variable)
i.e. BKN V SCT, VIS 2V3 [2 variable 3 miles], CIG 025V030 [2500 ft-3000ft])

- Lightning (Frequency_LTG-type)
    CG: Cloud to ground
    IC: Intracloud
    CC: Cloud to Cloud
    CA: Cloud to Air
    OCNL: Occasional
    FRQ: Frequent
    CONS: Continuous

- Beginning/Ending of Thunderstorms/Rain/Snow (TSB, SNE, RAB, etc)

- Thunderstorm Location (TS_LOC_(MOV_DIR)
    LOC=Location (N, NE, S, VC, OHD [Overhead], ALQDS [All Quadrants])
    DIR=Direction (N, NE, S, etc)

- Hailstone Size (GR_[size])

- Virga (VIRGA_[ DIR])

- Cumulonimbus or Cumulonimbus Mammatus (CB or CBMAM_LOC_(MOV_DIR).

- Towering cumulus (TCU_[DIR])

- Altocumulus castellanus (ACC_[DIR])

- Standing lenticular or Rotor clouds (CLD_[DIR])

- Pressure Rising or Falling Rapidly (PRESRR/PRESFR)

- Sea-Level Pressure (SLP###) (QNH in international METARS, no need to make this a remark there)

- Aircraft Mishap (ACFT_MSHP)

- Snow Increasing Rapidly (SNINCR_amount this hour/total)

- Hourly Precipitation Amount (P####).

- 3- and 6-Hour Precipitation Amount (6####)

- 24-Hour Precipitation Amount (7####).

- Snow Depth on Ground (4/###)

- RVR (Runway Visual Range, Rrrr/####ft) - will eventually be in the body!
    R=RVR
    r=runway, i.e. 31C, 21L, etc.
    ####ft=Distance of visual range (i.e. 6000ft, P6000ft [plus], m600ft [minus])


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