• What is a METAR and what is it used for?

    Meteorological routine report

We have already talked about the importance of knowing about winds in aviation and in today’s post we will take concepts a step further and tell you about METAR meteorological reports.

It is imperative that pilots know about meteorology with precision when flying. This is why METAR reports were created: it is a meteorological information system that explains the atmospheric conditions briefly and concisely at the time the report is elaborated. In Spain, METAR reports are emitted every 30 minutes.

But we’d like to take it a step further and answer all your questions about METAR reports: What they are, how to read one correctly, what other types of meteorological reports exist and we even suggest practical exercises for you to learn the concepts much more easily. So, if you’re interested, please read on!

What is a METAR and where does this word come from?

A METAR is a brief report in the form of an alphanumeric code which provides detailed meteorological information about a specific airport at a given time. It’s basically a series of letters and numbers which are issued periodically by airports and aerodromes.

Their name is taken from the French METéorologique Aviation Règulière; translated into English as Meteorological Aerodrome Report. You can now see why it’s been shortened to METAR, can’t you?

METARs are made up of different blocks, each of them is assigned a meteorological phenomenon: wind, clouds, temperature or atmospheric pressure, among others.

But don’t worry, following we gradually introduce the structure of METARs, block by block so that it can be easily understood.

How to read a METAR correctly

Knowing about the information given in each of its blocks is indispensable in understanding METAR reports. Let’s take a closer look at the example and analyse it in detail:

LEMG 211200Z 10013G23KT 9999 SCT014 BKN025 15/12 Q1020 NOSIG

  • Airport:

It is shown in the first block by its corresponding ICAO code.

In the example, Malaga International Airport’s code, LEMG, is provided.

  • Date and time:

The second block gives alphanumeric information about the day and time, the latter, expressed in UTC format.
In this case, the sample was issued the 21st (April, although the month isn’t given) at 12:00Z (Zulu time or UTC)

  • Wind:

Direction is measured in degrees, based on the true north and is expressed by the first two numbers of the third block of the METAR. The following numbers show speed expressed in knots.
In the example, we have wind from 100º with an average speed of 13 knots and gusts (G) of up to 23 knots.

  • Visibility:

Visibility can be found on the fourth block in METAR reports and is expressed in metres.
When it is under 1000 metres, we call it fog whereas when it´s between 1000 and 5000 metres it’s termed mist. We measure visibility in 500s (metres) and when it’s over 5000 metres, in 1000s. When it’s over 10km, it will show as 9999 in METAR.
Let’s go back to our sample to confirm that on the given date and time there was excellent visibility to fly.

  • Runway Visual Range RVR:

Runway visual range or RVR is what the block following visibility shows. This value gives information about the horizontal visibility a pilot has from the cabin.
RVR is only used in foggy conditions or poor visibility and is measured in three runway areas: header, half and end. In our example we can see that on the given day, the visibility was excellent.

  • Cloudiness:

In the next block we find cloudiness and this is probably the most complex point if you are not familiarised with METARs. The abbreviated words give information about how covered the sky is, based on a scale which is expressed in oktas and breaks up as follows:

SKC: Clear sky; 0 oktas covered.
FEW: Few clouds; between 1 and 2 oktas covered.
SCT: Scattered clouds; between 3 and 4 oktas covered.
BNC: Broken (abundant clouds); between 5 and 7 oktas covered.
OVC: Overcast (covered sky); 8 out of 8 oktas covered.

After its corresponding acronym, the next information block shown in METARs is the altitude of clouds in respect to the height of the airport, given in feet. We have to add 2 zeros (00) to the right of this value to obtain the real altitude.

In our example, we have scattered clouds at 1400 feet and abundant clouds (BNC) at 2500 feet.

  • Temperature and dew point:

Temperature in METARs is indicated in degrees centigrade and its relation to dew point is important. Dew point is the temperature at which air saturates, forming fog. Fog appears when the difference between room temperature and dew point is under 2ºC.
Going back to our reference METAR, we’ve got 15ºC and 12ºC dew point. There is no risk of fog formation with a difference of 3ºC between both values.

  • QNH:

The following METAR block provides a Q code which indicates the pressure at the airport, measured in hectopascals. This data is essential to figure out the aeroplane’s altimeter and therefore, be able to establish the approach minimums. In our example, we have a QNH of 1020 hectopascals.

  • Forecasts:

What about the last block? It’ll be there at times, but not always. In this case NOSIG indicates no significant changes in meteorology are expected in the next 2 hours.

Practical cases to learn how to read a METAR report

If you’ve been paying attention, we’re pretty sure you’ll have no problem interpreting the following METAR reports we suggest below… Try not to peek at the answer!

LEMD 211230Z 16010KT 140V210 9999 FEW020 BKN055 13/09 Q1020 NOSIG

A METAR report from Adolfo Suárez Madrid-Barajas, emitted the 21st at 12:30 UTC. We have wind with predominant 160º direction and speed of 10 knots; variable direction between 140º and 210º. Good visibility of over 10km. Few clouds at 2000 feet and abundant clouds at 5500 feet. With a temperature of 13º and dew point of 9ºC. QNH is 1020, without significant changes in the following 2hrs.

LEBZ 211230Z 09008KT 9999 FEW015 SCT025 OVC045 13/13 Q1016 RERA

This METAR report is from Josep Tarradellas Barcelona – El Prat and was issued on the 21st at 12:30 UTC. Wind with 90º direction and speed of 8 knots. Visibility is 10km or over. Scattered clouds at 1500 feet, disperse at 2500 feet and covered sky at 4500 feet. Temperature is 13ºC and the dew point is 13ºC. With a QNH of 1016 and rain forecasted.

SARI 011700Z 36002KT CAVOK 24/20 Q1022

We now take you a step further. This METAR report was issued by Iguazu Airport (Argentina), on the 1st at 17:00 UTC. With north wind at 2 knots, CAVOK*. The temperature is 24ºC, dew point 20ºC and an atmospheric pressure of 1022 hectopascals.

* CAVOK: Clouds and visibility OK is an acronym that indicates visibility is over 10 km, there aren’t any clouds below 5000 feet or the minimum altitude of the sector. It also indicates a lack of cumulonimbus or towering cumulus and no significant phenomenon is expected within the following 2 hrs.

Who prepares the METAR reports?

At all airports there is a meteorological department in charge of producing forecasts and METARs. To do so, they use a wide range of instruments: ceilometers to detect cloud height, transmissometers to measure RVR, visibility sensors, anemometers, humidity and temperature probes, weather vanes, etc.

In the case of Spanish airports, the State Meteorological Agency, AEMET, is responsible for preparing and issuing METAR reports every 30 minutes.

How to access METAR

Prior to flying

Pilots can check METAR through AEMET’s AMA’s web.

AMA or Autoservicio Meteorológico Aeronáutico, allows pilots to access meteorological METAR reports, wind and temperature maps, warnings and other significant maps.

On the aeroplane

Once on the aeroplane, METARs can be obtained from ATIS or Airport Terminal Information Service.

ATIS is a frequency at some airports to transmit important operational information, as well as meteorological information. At smaller airports, air controllers facilitate this information to pilots.

In-flight

VOLMET are frequencies used up in the air where METARs are issued from various airports. When flying, pilots frequently check VOLMET reports in order to find out the meteorological conditions of the area they are flying over in case it is necessary to divert to another airport.

Commercial aeroplanes also possess ACARS or Aircraft Communications Addressing and Reporting Systems; a function of CPDLC, which is a data link between pilots and air controllers and allows pilots to obtain METARs when already in flight. Some aeroplanes such as Airbus A320, are equipped with a small printer in the cabin so they can print out this type of information.

Other meteorological reports

As well as METARs, other kinds of meteorological reports exist, such as TAFOR and SPECI. But are they all the same? Not in the least. We go on to explain their differences.

SPECI

The issuing of SPECI reports is not programmed, i.e., they are created extraordinarily, when meteorological conditions change significantly at an airport. Really, they’re like METARs, but non-routine ones.

TAFOR vs METAR

Whereas METARs indicate the current meteorological conditions at the precise time they are issued, TAFs or TAFORs are meteorological forecast reports. Reading them is quite more complex. For example:

LEMG 220500Z 2206/2306 VRB03KT 9999 SCT020 SCT035 TX17/2214Z TN12/2206Z PROB40 TEMPO 2206/2208 BKN012 BECMG 2208/2210 13009KT TEMPO 2221/2304 12018G30KT TEMPO 2218/2306 4000 SHRA SCT025CB

Can you see how long it is? It’s a TAF from Malaga Airport and was issued on the 22nd at 05:00 Z and valid from the 22nd at 06:00 Z till 23rd at 6:00Z.

With variable direction wind of 3 knot speed and visibility of over 10km. Disperse clouds at 2000 and 3500 feet. Maximum temperature is 17ºC and will be reached on 22nd at 14:00 Z. Minimum temperature will be 12º, reached the 22nd at 06:00 Z.

There’s a 40% chance of broken (abundant clouds) at 1200 feet.

Between 08:00 and 10:00 Z on 22nd, there will be wind from 130º with 9 knots’ speed. Between 22nd at 18:00 and 23rd at 06:00, visibility is 4km, rain showers and dispersed cumulonimbus at 2500 feet.

What do you think? You probably think they are hieroglyphs but don’t worry, with practice they become really simple, we promise!