While you may check the Weather Channel, the TV, or (if you’re really old-fashioned) the newspaper for the weather forecast, when it comes to aviation a little more precision is required. Peoples’ lives are at stake, so it is paramount to have the most accurate weather information available for the pilots to operate their aircraft safely. This is where METARs come in. This accurate weather information is published every hour by airports and is communicated via a specific channel (ATIS) which is dedicated to airport information and weather.
A METAR is a coded description of the weather conditions at a certain place and time. A METAR always starts with these things first: the place, and the time. Let’s look at an example to make things easier.
The best way to learn how to read a METAR is to look at a real example.
Firstly, we have the place: EGBB. This is the ICAO airport identifier for Birmingham Airport (UK). You may be familiar with airport codes already, but it’s important to make a distinction between ICAO codes and IATA codes.
ICAO codes are used by pilots and comprise 4 letters (e.g. EGLL = London Heathrow). They follow somewhat of a pattern depending on the continent or country. For example, ICAO codes in the UK generally start with “EG**” and in Germany with “ED**”. However, there is no steadfast rule to determine the ICAO code of an airport, as sometimes they follow no discernable pattern at all (e.g. EGNM = Leeds Bradford Airport).
The other type of code, which you may be more familiar with, is IATA codes. These codes are generally used by travel agents / airlines and comprise 3 letters. In comparison with ICAO codes, IATA codes are usually closely linked to the name of the airport or city. To refer to our examples in the previous paragraphs, the ICAO code for London Heathrow Airport is EGLL but its IATA code is LHR. The ICAO code for Birmingham Airport (UK) is EGBB but its IATA is BHX. The ICAO code for Leeds Bradford Airport is EGNM but its IATA code is LBA. As you can see, IATA codes are much more recognisable than ICAO codes.
So, we have identified the first element of the METAR: the place (EGBB).
The second element refers to the time of the weather observation. In our example, this is “211450Z”. While at first glance this may appear to be gibberish, it’s actually quite simple. The first 2 numbers refer to the day of the month. In our case, it’s the 21st day of the month, as that is the day I am writing this article. The next 4 letters refer to the actual time the observation was made. In our example, the observation was made at 1450 (i.e. 2:50PM). This element ends with a “Z”, which means Zulu Time, or Greenwich Mean Time (GMT) in other words. This is standard practice around the world, so you must take into account time zones.
So, we have identified that our METAR is for Birmingham Airport (UK) and the observation was made at 14:50GMT on the 21st day of the month (i.e. today at the time of writing). The elements that follow concern weather observations.
The third element in our METAR is “07013KT”. This refers to the wind. The first 3 numbers are the wind direction (070 degrees) and the other two numbers and letters concern the wind speed (13 knots). Sometimes the wind direction and speed are not always steady, and this is also included in the METAR, but we will look at this later in the guide.
So, from our EGBB METAR, we have now identified that at Birmingham Airport UK, today at 2:50PM, the wind was observed as 070 degrees at 13 knots.
The fourth element in our METAR is “CAVOK”. If you see this, you can be happy. It means “Cloud and Visibility OK”. This means there is no cloud or other significant weather below 5,000ft. This is comparison with the abbreviation "SKC", which means "sky clear". We will look at other cases where there is cloud and visibility information in the METAR later in this guide so you can learn how to read METARs which are more complex.
The fifth element in our METAR is “17/04”. These two numbers refer to the outside temperature and dew point respectively. If the temperature is negative, it will have an M before e.g. M03 = minus 3 degrees Celsius. Temperatures and dew points are always expressed in Celsius no matter where you are in the world. Even in the US, the METAR will indicate the temperature and dew point in Celsius, not Fahrenheit.
The sixth and final element in our METAR is “Q1018”. This refers to the air pressure in millibars. Q stands for “QNH” which is a code used to indicate atmospheric pressure adjusted to mean sea level. It is important to know the QNH so you can set your altimeter correctly. With air pressure, the code is not standardised around the world. In the US, Canada, Mexico and Colombia, air pressure is measured in inches of mercury (inHg). If our example were a METAR from any of these countries, we would see “A3006” instead of “Q1018.
So, with all this information, we’ve learned how to read a basic METAR!
Although our previous example one was quite a simple one, all METARs generally follow the same format. Now let’s look at a more complex example:
This METAR includes some new elements which we didn’t see in the previous example. Let’s look at each part piece by piece.
From what we learned in the first part of this guide, we can infer that this METAR is for Málaga Airport and the observation was made on the 21st at 1800 GMT. We can also analyse the wind and see that the wind direction is 240 degrees and wind speed is 3kts.
However, we have a new element after the wind: 200V300. This means that the wind direction is variable, from 200 to 300 degrees. This information always comes directly after the standard wind information.
In this example we don’t have CAVOK. Instead, we have some visibility and cloud information. The first one – “9999” – means that visibility is greater than 10km. The use of “9999” is very common as visibility is not measured above 10km. This element is measured in meters, so if we see “5000” for example, that means the visibility is 5km. The exceptions to this are the US, Canada and Mexico, where visibility is expressed in statute miles e.g. 10SM.
Following the visibility information, we have information about the clouds. This LEMG METAR shows 2 cloud elements. Let’s look at the first one: FEW025. FEW is almost self-explanatory: it means few clouds. The numbers following FEW indicate the altitude of the clouds in feet. In this case, there are a few clouds at 2,500 feet. You can probably infer the meaning of the second cloud element: SCT060. This means scattered clouds at 6,000ft.
The rest of the METAR was covered in the first part of the guide with the exception of the final element: NOSIG. This means that no significant changes are expected within the next 2 hours. It's one of various codes used, which we look at in more detail later.
That's it! Now you know how to read a standard METAR.
In the first part of this guide, we discovered CAVOK. In the second part, we discovered visibility and clouds (FEW and SCT). However, as you read more METARs you will see more and more codes for clouds, so here is a comprehensive list of them:
|SKC||Sky clear (human check, no clouds)|
|CLR||Sky clear (automatic, clear up to 12,000ft)|
|NCD||No cloud detected|
|NSC||No significant cloud|
|SCT||Scattered (3/8 - 4/8)|
|BKN||Broken (5/8 - 7/8)|
So far we have discovered how to read METARs and decode wind, cloud and visibility data. Now we are going to look at an example which introduces some new elements.
We have already covered most of the items in this METAR, so let’s just look at the new ones. The first new element is “-RA”. This means “light rain”. The minus sign before “RA” indicates the intensity. So “RA” would be mean moderate rain and “+RA” would mean heavy rain. At the end of this part we will look at a table with all the possible abbreviations (snow, mist, etc).
The second new element is “TCU” at the end of “FEW018”. This means towering cumulonimbus, which is a vertical cloud with strong upward currents and is often accompanied by heavy rain or thunderstorms. It's important to note that "FEW" indicates the cloud coverage, and "TCU" indicates the cloud type.
The next new element in this METAR is “TEMPO”. This indicates that a change in the weather conditions is about to happen, and it will happen before the next weather observation. So let’s look at these temporary conditions.
First, we have 2000, which as covered previously, means the visibility is 2 kilometers. TSRA means thunderstorm with rain. BKN means broken clouds at 1,200ft and BKN050CB means broken cumulonimbus clouds at 5,000ft.
Now we've covered most of the basics of METARs and looked at some complex examples, let's look at the different types of abbreviations used (like the abbreviation RA in our last example).