If flying is among your passions, knowing how to read a METAR is of fundamental importance as weather plays a major factor in the development of your flight. In this METAR reading guide I will provide and explain the information You need to know about how to read a METAR in most of the cases and to fully comprehend it. Reading a METAR may seem complex and difficult when You see a METAR for the first time, but once You learn the meaning of the most common METAR abbreviations and get used to the standard METAR format You will see that reading a METAR is not that hard at all - actually it is really easy.
Before proceeding, is fundamental that You first understand what is a METAR, how long is a METAR valid for and how often are METARs published.
What does METAR stand for?
The METAR acronym stands for Meteorological Terminal Air Report.
What is a METAR?
A METAR is a meteorological observation of the weather at an airport; pay attention to the fact that is not a forecast, is an instantaneous observation, a snapshot which indicates how the weather was when was taken. Because the METAR is a "weather snapshot" and not a "weather forecast", its validity in time is zero.
How long is a METAR valid for?
METARs have no validity in time. The aviation meteorological message which has validity in time is the TAF, which can be valid from nine to twelve hours since the moment in which is published, but the validity of METARs in time is zero.
How often are METARs published?
METARs are published every 60 minutes at minor airports and every 30 minutes at major airports.
The standard METAR format looks like this:
ICAO -> Date and zulu time -> Wind -> Prevailing horizontal visibility -> Vertical visibility -> Temperature -> Pressure -> Possible remarks -> Possible "trend" part
The above format is the one that a METAR always respects; in case one or more parts are missing, it will just pass to the next one.
Example of standard METAR format (without remarks and without trend part):
EGLL 071700Z 15012KT 7000 SCT032 15/09 Q1013
Now I am going to explain each of these parts and the METAR abbreviations that is possible to find in each of them.
Is the four letters airport code.
Date and Zulu time
Day of the month and Zulu time when the METAR was published.
Format example: "071700Z" - 07 is the day of the month; 1700 is the Zulu time (hour and minutes).
The main METAR format in which wind is displayed is (example): "15012KT" - 150 is the direction where it comes from; 12 is the intensity; KT is the unit in which the wind intensity is measured (it can be KT for knots, MPS for meters per second, KMH for kilometers per hour).
Other three formats in which wind is displayed in METARs:
1. "15012KT 120V180" - 120V180 indicates that the direction where the wind is coming from changes between 120 and 180 degrees.
2. "VRB02KT" - the VRB abbreviation stands for variable; this wind format indicates that the wind direction is variable (usually this is found with low intensity values, below 3 kt).
3. "15012G25KT" - the G abbreviation stands for gusts, the number after (in this example 25) stands for the maximum intensity of the gusts. Gusts are measured for at least three seconds, with an intensity of at least 10 knots stronger than the wind's.
Prevailing horizontal visibility
Can be shown in meters, in SM (static miles) or represented with one of the following two METAR symbols: "9999" when the visibility is 10000 meters or more, or "CAVOK" (which stands for "ceiling and visibility okay") when the visibility is 10000 meters or more and there are no clouds below 5000 feet.
Examples of horizontal visibility formats in METARs:
"7000" - horizontal visibility of 7000 meters;
"10SM" - horizontal visibility of 10 static miles;
"9999" - horizontal visibility of 10000 meters or more;
"CAVOK" - horizontal visibility of 10000 meters or more and no clouds below 5000 feet.
Is expressed with clouds' coverage and their height from ground.
The METAR abbreviations which indicate the coverage of the clouds are four:
"FEW" - when sky is covered between 1/8 and 2/8 of its area;
"SCT" - METAR abbreviation which stands for scattered clouds, and is used when the sky is covered between 3/8 and 4/8 of its area;
"BKN" - METAR abbreviation which stands for broken clouds, and is used when the sky is covered between 5/8 and 7/8 of its area;
"OVC" - METAR abbreviation which stands for overcast, and is used when the sky is completely covered (8/8 of its area).
Clouds' height from ground is written in hundreds of feet.
In METARs clouds can be written even more than one time.
Example of vertical visibility format: "SCT032" - SCT indicates there are scattered clouds, 032 indicates that the clouds are at 3200 feet.
When there are relevant clouds like Cumulus Nembus and Towering Cumulus we find the METAR symbols "CB" for Cumulus Nembus or "TCU" for Towering Cumulus written next to the cloud's height.
Another example of vertical visibility format: "BKN027CB" - BKN indicates there are broken clouds, 027 indicates that the clouds are at 2700 feet, CB indicates that the type of clouds are Cumulus Nembus.
When there are no clouds but is still not possible to use "CAVOK", we will find written the "SKC" METAR abbreviation which stands for "sky clear".
Between the prevailing horizontal visibility and the vertical visibility we can find one or few symbols which will indicate if there are any particles in the air (like water or smoke for instance).
Here is a list of METAR symbols that is possible to find.
METAR symbols indicating the intensity of the phenomenon
METAR symbols indicating the way in which the phenomenon happens
METAR symbols indicating possible weather phenomena
"SG" snow grain
"PE" ice pellets
"IC" diamond dust that causes visibility to be reduced to less than 5000 meters
"GR" hail with diameter bigger than 5 millimeters
"GS" small hail or snow pellets
"PY" sea spray
"VA" volcanic ash
"PO" dust devil
"FC" funnel cloud
"DS" dust storm
"SS" sand storm
"TS" thunder storm
* "VC" means in the vicinity of the airport.
* "UP" means unknown precipitation.
Other examples of vertical visibility formats in METARs:
"BR FEW015 BKN070" - mist, few clouds at 1500 feet, broken clouds at 7000 feet.
"FEW008CB BKN175" - few Cumulus Nembus at 800 feet, broken clouds at FL175.
"BR SKC" - mist, sky clear.
"+BLSN SCT013 OVC017" - heavy blowing snow, scattered clouds at 1300 feet, overcast at 1700 feet.
"SHRA BKN007CB" - showering rain, broken Cumulus Nembus at 700 feet.
Is written the temperature of the air and the dew point, both in Celsius degrees. If the temperature is below zero then the symbol "M" is placed in front of the number.
Examples of temperature formats in METARs:
"15/09" - air temperature plus 15 degrees, dew point plus 9 degrees.
"03/M01" - air temperature plus 3 degrees, dew point minus 1 degree.
Closer to the air temperature the dew point is then more humidity is it in the air.
Can be displayed in two formats, in Hg inches or in Hpa.
The reference point of the atmospheric pressure is: 29.92 inches Hg = 1013 Hpa.
If displayed in Hg inches, the pressure METAR format will look like "A2992", while in Hpa the format will look like "Q1013".
Usually low pressure values (below 29.92 = 1013) are sign of bad weather while high pressure values (above 29.92 = 1013) are sign of good weather.
This section is optional and starts with the METAR symbol "RMK". Here is indicated any additional possible information.
Possible "trend" part
In this optional section is indicated the weather tendency. Its validity starts from the time when the METAR was published and lasts for two hours.
The "trend" section can have any of the following METAR symbols:
"FM" from a specific time, "TL" until a specific time, "AT" at a specific time, "BECMG" becoming, "TEMPO" temporary change which lasts less than one hour, "NO SIG" no significant change of the observed weather in the following two hours.
The information I explained in this METAR reading guide allows You to understand how to read a METAR in most of the cases, however besides what I covered in this METAR reading guide there is more information that is used in METARs in some rare cases so is your responsibility to do more research to be better prepared before beginning your flight.
By Claudio Adriano Dobre, © 2010