Decoding METAR information

Photo: NOAA [pd]

We are not certain this is a true fact, but it seems that at some point way back in history the FAA decided that the average American aviator is just too damn stupid to know what the word meteorological means.

So they redefined the meaning of METAR to "Aviation Routine Weather Report", even though that is not what the acronym stands for. You can always trust a government agency to find some way to make anything more complicated and confusing.

If it was called an AVROWER then the FAA definition would be logical. The proper definition of METAR is "Meteorological Terminal Air Report". Doesn't that make a lot more sense? But, what the heck... a weather report is a weather report!

Like almost every other transmission in aviation communications, the METAR information is encoded, and it can take a bit of practice to become really familiar with how to read and understand the information provided.

But fear not — we've provided a handy example below to help you figure out just what the METAR is trying to tell you.

For the first example, we will look at a US style METAR code:

KMSP 231953Z 25014G20KT 10SM SCT033 BKN300 27/18 A2980 RMK AO2 SLP084 T02720183

Data Meaning
KMSP station (Minneapolis-St Paul Intl)
231953Z day of month (eg 23) & time (19:53 Zulu)
25014G20KT wind direction is 250° at 14 knots with gusts up to 20 knots
10SM visibility is 10 statute miles
SCT033 scattered clouds, with the lowest cloud layer at 3300ft.
BKN300 "broken" clouds, with the lowest cloud layer at FL300.
27/18 OAT is 27°C and the dew point is 18°C.
A2980 Altimeter setting is 29.80 in Hg
RMK Everything following this is a remark.
A02 This station is equipped with an automated sensor that can tell the difference between rain and snow.
SLP084 Sea Level Pressure is 840 hPa
T02720183 Temperature code

That last item, the Temperature Code, also needs some further explanation:

Data Meaning
T Identifies this as a Temperature Code
0 This means the temperature is above 0°C. A value of 1 means the opposite.
272 OAT is 27.2°C
0 This means the dew point is above 0°C.
183 Dew point is 18.3°C.

Outside the US, the METAR codes are slightly different, but still follow the same basic pattern. Here is an example of a METAR for Amsterdam International (Schipol):

EHAM 232000Z 25004MPS 800 R24/0600N R36/0600N +RA OVC040 02/06 Q1019 NOSIG 88290291

Some of the international METAR data is equivalent to the US style. One thing that is quite different is that there is a lot more runway-specific data included. Here's the breakdown:

Data Meaning
EHAM station (Schipol Amsterdam Intl)
232000Z day of month (eg 23 June) and time (20:00 Zulu)
25004MPS wind from 250° at speed of 4 meters per second
800 prevailing visibility is 800m
R24/0600N visibility on runway 24 is 600m, not expected to change before next read.
R36/0600N visibility on runway 36 is 600m, not expected to change before next read.
+RA it's raining (RA), heavily (+).
OVC040 overcast cloud cover to height of 4000ft.
02/M01 the OAT is 2°C and the dew point is -1°C.
Q1019 QNH is 1019 hPa (for altimeter setting)
NOSIG No significant change in conditions is expected before the next read.
88290291 All runways (88) are affected by rain (2) and have up to 2mm of surface water (02). Braking conditions are poor (91).

88 is a code used to include all runways, but specific runways could also be reported in the same way, only the number would be in the range from 01 to 36, because these are the only valid runway numbers (with L, R, and C variants). Looking at the above data, there should be no chance you would want to fly into or out of Schipol with conditions like these.

The above is just a brief introduction to reading and understanding METAR information, but it is a really big topic, so we may return to it later in a future update.