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METAR Decoding

METAR’s are different from TAF’s in that they are actual weather reports and not forecasts for a given airfield, indeed they are sometimes refered to as ‘Actual’s’. They appear in the same format as TAF’s and share many common codes, with a few extra groups thrown in. When planning a route it’s vital to know what the weather is doing at the destination airfield, so by using a combination of TAF’s and METAR’s we can gain a complete picture on the weather situation. A useful example of this might be to look at a TAF for your destination airfield and from that you might identify that some frontal weather might be crossing the region, if you then refer to a METAR for an airfield near the direction that the front is coming from, you’ll be able to establish wether or not the front has reached there yet and how long approximately you may have to complete your flight. Take a look at the example below….

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

As in the TAF described in the other section, the METAR is broken down into coded sections. The first section is the date (day of the month) and time of the METAR issue. As we can see from the above example it’s in the same format as the TAF, in this case it was issued on the thirtieth of the month at 1220hrs (again don’t forget that it’s 1220hrs GMT, Zulu or UTC, so if the UK is on British Summer Time (BST) then we must add an hour to the issue time to make up for the difference).

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

The second section is the ICAO identifier for the airfield in question (see the downloadable list of identifiers for the UK – the ones marked with an issued TAF in the right hand column will also have a METAR issued for it). So from our list we can see that the airfield that this was issued for is Exeter.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

Group three of the METAR deals with the reported wind direction and speed (same as the TAF) You’ll see from the above example that that the observed wind was blowing from 300deg at a mean speed of 25 knots with a maximum gust of 37 knots (it’s well to note that if the maximum gust is less than 10 knots then only the mean speed is reported) The other code is again the same as the TAF and this states that the wind was not blowing from a constant direction but veering between westerly (270deg) and northerly (360deg) these are always reported in a clockwise direction.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100

Group four concerns reported visibility for and sometimes gives two figures. These are the reported minimum and maximum and the given direction using the eight point compass (i.e N, NE, E, SE, S, SW, W, NW) So in our example the minimum reported visibility is 1200 metres towards the North East.

Similarly, if you saw the codes grouped like this 1200NE 1800S would indicate 1200 metres to the northeast and 1800 metres to the south of the airfield. If you read the TAF decode section you’ll have seen 9999 this means that the reported visibility is greater than 10km’s.

Although we have’nt shown it in our standard example I’ve included the section below that deals with RVR or Runway Visual Range. This figure is only included in the METAR if the observed runway visual range is below 1500 metres, so for our purposes if you see this figure then choose another airfield!!

301220 METAR EGTE 30025G37KT 270V360 1200NE R23/0900 +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

In our example this indicates that for the current runway in use, Runway 23 the RVR is only 900 metres (If you applied this to Dunkeswell it would effectively mean that when standing on the 23 numbers, you could’nt see the end of the runway!!). You may also see it coded like this R23/0900V1300 which indicates any variations in the visual range.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

Group six of the METAR gives any observed weather at or near the airfield in question and is reported in the same way as in the TAF (in our example +SHSN means heavy snow showers), but there are some additional codes that you can see listed below:

  • RA – Rain FC Funnel Cloud
  • DZ – Drizzle DR Drifting
  • GS – Small Hail BL Blowing
  • GR – Large Hail (>than 5mm) PL Ice Pellets
  • SH – Showers SA Sand
  • SN – Snow MI Shallow
  • SG – Snow Grains FZ Freezing
  • TS – Thunderstorm IC Ice Crystals
  • SQ – Squall DU Dust
  • BR – Mist FU Smoke
  • FG – Fog HZ Haze
  • PR – Banks BC Patches
  • + Heavy
  • – Light

There are few more codes that you’ll probably never see when flying around this country and they are:

  • DS – Dust storm
  • SS – Sand storm
  • PO – Dust Devils; and finally one that we hope we’ll never see
  • VA –¬†Volcamin Ash!

There may be up to three groups of the above grouped together made up of a combination of the above, you can see a few examples below :-

  • +SHRA = Heavy showers of rain.
  • PCBR = Mist patches
  • DRSN = Drifting snow.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

Group seven concerns the reported cloud and this takes the same form as we have seen in the TAF’s, so it’s measured in Okta’s and altitudes indicating any layers. So in case you have’nt read the TAF decode section then :

  • SKC = Sky clear (0 Okta’s – O eighth’s)
  • FEW = Few (1-2 Okta’s – 1 to 2 eighth’s)
  • SCT = Scattered (3-4 Okta’s – 3 to 4 eighth’s)
  • BKN = Broken (5-7 Okta’s – 5 to 7 eighth’s)
  • OVC = Overcast (8 Okta’s – 8 eighth’s)

Whilst you’ll see the cloud coverage and cloud base reported you’ll only see two cloud types. They are

  • TCU = Towering Cumulus
  • CB = Cumulonimbus

You’ll probably see multiple groups of codes together, so in our example¬†SCT005 BKN010CB would indicate a layer of cloud at 500ft with 3-4 okta’s coverage, a layer of cloud at 1000ft with 5-7 okta’s coverage with Cumulonimbus clouds present. Again if there is no cloud below 5000ft and the visibilty is greater than 10km’s you will see the word CAVOK replacing the visibilty, weather and cloud groups.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

Group eight of the METAR gives you the reported temperature and dewpoint (in degrees Celsius) at the airfield in the following format temp/dewpoint (normally in degrees Celcius). So in our example above the reported temperature was 3deg Celcius and the dewpoint was -1deg Celcius (below freezing temperatures are preceded by the letter ‘M’)

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

Group nine gives the current airfield pressure setting (QNH) in millibars (rounded down to the nearest whole milibar). So the airfield QNH for Exeter at the time of reporting was 999 milibars.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

Group ten gives any recent weather at the airfield and is given in the same format as the present weather as shown in group six. So as you can see in the above example that since the last report that Exeter suffered a Thunderstorm.

301220 METAR EGTE 30025G37KT 270V360 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 NSW SCT015 BKN100=

  • BECMG = Becoming
  • TEMPO = Temporarily
  • FM = From
  • TL = Until
  • AT = At

The above codes will normally be followed by a time period and then further visibility, significant weather and cloud data. We can see from our example that at 1300UTC that the bad weather will be clearing to leve No Significant weather and the cloud base will be lifting to 1500ft (3-4 Okta’s coverage) with a further layer at 10,000ft (5-7 Okta’s).

There maybe another group that you’ll see at the very end of the METAR and this is an eight figure code that shows the Runway state. This contains such information as type of contamination (Snow, Ice etc.), depth of contamination, Surface friction (braking efficiency etc.), but for our purposes this won’t mean a lot, so I won’t go into it here.