Informations about METARs

Informations

A METAR is a coded format message, for reporting weather information. It is the most popular format in the world for the transmission of weather data. Depending on what weather is occuring during the time of the observation, a metar can be complex or very complex. It is highly standardized through International Civil Aviation Organization (ICAO), which allows it to be understood throughout most of the world.
METAR's are mainly used by pilots for weather briefing and by meteorologists in weather forecasting. The METAR format was introduced 1 January 1968 internationally and has been modified a number of times since. The World Meteorological Organization's (WMO) publication "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the (WMO) member countries.
The definitions for the term METAR are many. The World Meteorological Organization (WMO), which is the international authority for the code form, holds the definition to be "Aerodrome Routine Meteorological Report". For the United States Federal Aviation Administration (FAA) the definition is "Aviation Routine Weather Report". METAR is also known as "Meteorological Terminal Aviation Routine Weather Report" or "Meteorological Aerodrome Report".
METARs typically come from airports or permanent weather observation stations. Reports are generally generated once an hour, but if conditions change significantly, a report known as a special (SPECI) may be issued.
METARs are encoded, or by automated airport or other weather stations and then reviewed by certified weather observers or forecasters prior to being transmitted, or by trained observers or forecasters who observe and encode their observations prior to transmission.

Decoding a METAR

Below is an example of an international METAR

  METAR LGTS 041600Z 12003MPS 310V290 1400 R16/P1500N R34/P1500U +SN BKN022 OVC050 M04/M07 Q1020 NOSIG 8849//91= 

CODE PART Explanation
 METAR  Type of the report. Here the type is METAR.
 LGTS        4-Letter ICAO code identifier. LGTS stands for Thessaloniki airport "Makedonia".
 041600Z 
  		The day and time of the observation. Here we have the 4th(04) day of the month and the time is 16:00(1600) Zulu(z) time.
 12003MPS 
  		The wind direction and wind speed. Here the wind comes from 120°(120) at a speed of 3(03) meters per second(MPS).
 310V290 
  		The wind direction variation. Here the wind direction is varying(v) from 310°(310) to 290°(290).
 1400  The prevailing visibility. Here the visibility is 1.400(1400) meters.
 R16/P1500N 
  		The Runway Visual Range (RVR). Here the RVR(P) along runway(R) 16(16) is 1.500(1500) meters and not changing significantly(N).
 R34/P1500U 
  		The Runway Visual Range (RVR). Here the RVR(P) along runway(R) 34(34) is 1.500(1500) meters and rising(U).
 +SN  The precipitation type. Here snow(SN) is falling at a heavy(+) intensity.
 BKN022 
       		The sky cover. Here we have a broken(BKN), over half the sky, cloud layer with its base at 2.200(022) feet above ground level.
 OVC050 
       		The sky cover. Here we have an unbroken(OVC), overcast, cloud layer with its base at 5.000(050) feet above ground level.
 M04/M07 

  		The temperature and dewpoint. An M in front of the number indicates that the temperature or dew point is below 0°C. Here the temperature is -4°C(M)(04) and the dewpoint is -7°C(M)(07).
 Q1020 
  		The altimeter setting QNH pressure (barometric pressure adjusted to sea level). Here the QNH(Q) is 1.020(1020) hPa.
 NOSIG 
  		The expected conditions. Here no(NO) significant(SIG) change is expected to the reported conditions within the next 2 hours.
 8849//91 


       		The condition of the runway or runways. Here all(88) the airport's runways are coated with dry snow(4) and covered is the 51% to 100% of the runways surface(9). Also the thickness of the coating is not affecting the usage of the runways(//), but the braking index is bad(91).
 =  The end(=) of the METAR report.

METAR codes and their interpretation

Not all METAR codes are listed below. For more look here
REPORT TYPE
 METAR    This is the scheduled (routine) report     SPECI    This is the unscheduled (special) report
RUNWAY VISUAL RANGE (RVR)
 D    Down     U    Up     N    No change     V    Variable
INTENSITY
 -    Light          Moderate     +    Heavy     VC    In the vicinity
DESCRIPTORS
 MI    Shallow     PI    Partial     BC    Patches      *Only with fog e.g.  MIFG   
 DR    Low Drifting     BL    Blowing      *Only with snow, dust or sand e.g.  BLSN 
 SH    Shower(s)      *Only with rain, snow, ice pellets and small or large hail e.g.  SHRA 
 TS    Thunderstorm      *Itself or with rain, snow, ice pellets, small hail/snow pellets or hail e.g.  TSSNGS 
 FZ    Freezing      *Only with rain, drizzle or fog e.g.  FZRA 
PRECIPITATION
 DZ    Drizzle     RA    Rain     SN    Snow     SG    Snow grains     IC    Ice crystals
 PE    Ice pellets     GR    Hail     GS    Small hail/Snow pellets     UP    Unknown precipitation
OBSCURATION
 BR    Mist     FG    Fog     FU    Smoke     VA    Volcanic ash
 DU    Widespread dust     SA    Sand     HZ    Haze     PY    Spray
SKY COVER
 SKC    or  CLR    Clear     FEW    1-2 octas cover
 SCT    3-4 octas cover     BKN    5-7 octas cover     OVC    8 octas cover
SPECIFIC ABBREVIATIONS
 CAVOK    Ceiling And Visibility are OK
Visibility, cover and weather conditions codes are replaced by this code, when the following conditions exist simultaneously
● Visibility is 10km or more
● No CB or TCU and no cloud below 5.000 feet or Minimum Sector Altitude (MSA), has been observed
● No significant weather at or in the vicinity of the aerodrome

 NSC    No Significant Cloud
This code is used, when the following conditions exist simultaneously
● CAVOK code is not appropriate
● There are no clouds of operational significance
● There are no CB or TCU

 RAPID    Rapid change
A rapid change over a period less than 1/2 hour is expected

 NOSIG    No Significant
No significant change is expected to the reported conditions within the next 2 hours