A METAR, or aviation routine weather report, is an hourly surface observation from a weather station, usually at an airport. It gets its name from the term Meteorological Aerodrome Report, but boy is that a mouthful. In a nutshell, it’s what the weather is doing at the airport. The “raw” version of a METAR looks like a ticker tape of code – that is, until you learn to read it.  Nowadays, the magic of technology allows for a “decoded” version that does the work for you, putting it in an easy to read format. There are a ton of different elements of code that can show up in a METAR, but let’s look at a basic example that will cover a common scenario and let you get familiar with the format.

KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

Does that look like a bunch of nothing?  That’s ok.  By the end of this, you’ll be able to paint a picture of the weather. Let’s break down each element and see what it’s all about.

1. Location
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

The four digit airport identifier tells you where the report is coming from. Today’s METAR is from Athens, GA (KAHN).  The K means that it’s an American airport, so really you are reading the three digit airport identifier.

This Automated Weather Observing System (AWOS) at the Thomson Airport (KHQU) is the equipment that reads the weather to generate a METAR.

This Automated Weather Observing System (AWOS) at the Thomson Airport (KHQU) is the equipment that reads the weather to generate a METAR. Photo: Jake Pounds

2. Date & Time
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

The first two digits are the day of the month that the report was generated. In this case, the 6th. The last four digits are the time the report was generated.  In this case, 05:51AM.  The Z means Zulu time, also known as Greenwich Mean Time (GMT), or Universal Time Coordinated (UTC).  Basically, what time it is in England. Why do this? When you get in an airplane, it won’t take long to cross a time zone.  This keeps everybody on the same page with time no matter where you are.  Where I am, I’m four hours behind GMT, so to convert to local time, I just subtract four hours.  And it’s in 24 hour format, or military time.  Pilot hack: my watch, a basic Timex, will display a second time zone at the push of a button.  I have Zulu time set as the second time zone so I’m always a button press away from knowing the current Zulu time without any math.  The AUTO in the METAR means that the report was automatically generated by a computer, rather than with the aid of an observer.

Setting your watch to easily access a second time zone can make figuring out Zulu time as easy as pressing a button.

Setting your watch to easily access a second time zone can make figuring out Zulu time as easy as pressing a button.

3. Wind Direction & Speed
KAHN 060551ZAUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

Wind is measured by two things. The direction it is blowing FROM and the speed it is blowing. This wind in this example is “one eight zero at 10.”  The first three digits are the compass direction in degrees the wind is coming FROM. In this case, 180 degrees, or from the south. The speed is the next two digits measured in knots, or nautical miles per hour. Yeah, I know, that silent “k” really came out of nowhere going from “nautical” to “knot.”  A knot is 1.15 statute (meaning regular or not nautical) miles per hour, so this 10 knot wind is the same as 11.5 miles per hour.  A common variation of this is to see something like 18010G16KT.  The G means gust, so in this case the wind is from 180 degrees at 10 knots steady wind, gusting up to 16 knots.

Determining the direction and speed of the wind will determine which runway is in use.

Determining the direction and speed of the wind will determine which runway is in use.

4. Visibility
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

The visibility is simply how far you can see. Measured in statute (regular or not nautical) miles, there is usually a code just after the distance with what is causing limited visibility or precipitation, like rain (RA), fog (FG), or mist (BR).  To memorize the codes, we pilots come up with silly memory aids like “mist is Baby Rain” (BR). Silly, but it works.

Rain, fog, mist, and haze are just some of the elements that reduce visibility.

Rain, fog, mist, and haze are just some of the elements that reduce visibility.

5.  Clouds
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

You can read about the different layer types of clouds in my Its Always Sunny Outside blog.  The first three letters are the type of layer – clear (CLR), few (FEW), scattered (SCT), broken (BKN) or overcast (OVC). Then there are three letters that give the height above the ground that the layer starts (the bottom of the layer).  It is given in hundreds of feet, which means just add two zeros to get the height in feet.  In this case, OVC075 is “overcast at 7500 feet.”

I often find myself looking at the clouds and trying to guess their height. Then I check the nearest METAR to see if I'm right.

I often find myself looking at the clouds and trying to guess their height. Then I check the nearest METAR to see if I’m right.

6. Temperature & Dewpoint
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

Measured in Celsius, these two numbers are the temperature and Dewpoint. The temperature is not only useful for determining what sort of clothes to wear, but primarily for predicting airplane performance (for instance, hotter temperatures typically mean that more runway is used to takeoff and land). The temperature/dewpoint spread is the difference between the two numbers. With a low spread, look out for lower clouds or fog!

High temps can shut down phones and tablets, but more importantly they effect the performance of the airplane!

High temps can shut down phones and tablets, but more importantly they effect the performance of the airplane!

7. Altimeter Setting
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

The altimeter measures the altitude, or height, of the airplane. The altimeter setting is simply the pressure of the air measured in inches of mercury (abbreviated Hg). Just drop in a decimal right in the middle – in this case, 29.94Hg.  The altimeter of the airplane has a little window where this number can be selected with a knob (named the Kollsman Window after its German inventor). This makes the altimeter needle display the correct altitude despite changes in pressure.  For instance, Thomson Airport (KHQU) sits at an elevation of 500 feet. When starting up the plane, having yesterday’s altimeter setting in the Kollsman Window might cause the altimeter to read something like 515 feet because the pressure has changed.

As pressure changes, the altimeter setting is adjusted in the small window of the altimeter to ensure the altitude reads correctly.

As pressure changes, the altimeter setting is adjusted in the Kollsman Window of the altimeter to ensure that the altitude reads correctly.

8. Remarks
KAHN 060551Z AUTO 18010KT 3SM RA BKN010 OVC075 27/24 A2994 RMK AO2 SLP 131

The remarks (RMK) section is a general notes area where you can find all sorts of challenging to decipher code. In this case, the A02 is a common code that means that the METAR is being reported by automated equipment that can decipher the difference in rain and snow (as opposed to an A01, which cannot tell the difference in rain and snow).  The sea level pressure (SLP) is measured as 1013.1 millibars – you add a 10 before the first number and a decimal before the last number.

The remarks section often has things like LTG DSNT NW (meaning lightning distant to the northwest) and can hold clues to any adverse weather.

The remarks section often has things like LTG DSNT NW (meaning lightning distant to the northwest) and can hold clues to any adverse weather.

Breaking The Code
This has been a fairly straightforward and typical example of a METAR. There are many nuances and variations of this data, but the format and these basic principles remain the same. Here is a good guide if you wish to delve deeper into the different components.  Keep in mind, a METAR is an observation. It is not the big picture or a full weather forecast. A good pilot will use a METAR as just one tool in a large weather toolbox of assessing weather before a flight. Anytime heavy storms are coming through my area, I love to open up my Foreflight app and look at what all of the airports are reporting. If you weren’t watching the radar, you might not know that such bad storms were present from METARs alone.  Take a look at the image above with the storm showing in red and pink.  It’s pretty severe, and nobody should be flying anywhere near it, but look at all the green dots around it – those are airport weather stations showing visual flight rules (VFR) weather conditions through their METAR.  Like a language, practice reading METARs and expanding your knowledge of the different kinds of codes that can show up.  Oh, and I’ll leave you with the “decoded” version of the METAR we’ve been working with:

Athens Airport at 1:51AM Local Time, Wind 180 at 10 knots, Visibility 3 miles, broken clouds at 1000 feet, overcast clouds at 7500 feet, temperature 27 Celsius, dewpoint 24 Celsius, pressure 29.94 inches of mercury, remarks A02, sea level pressure 1013.1 millibars.

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