HOW TO READ METAR

HOW TO READ METAR, this is report actual weather observed at an airport. METARs are encoded in a standard format that can be understood internationally. There are slight differences between North American and International METARs but the format is generally the same, with different units of measurements used.

A METAR (Meteorological Terminal Air Report) is a routine aviation weather report of actual observed conditions at an airport. METARs report actual weather observed at an airport. METARs are encoded in a standard format that can be understood internationally.

HOW TO READ METAR

Spend any time around aviation types and the term METAR will likely come up. METAR is an acronym that stands for Meteorological Terminal Air Report, and it’s a highly practical way to transmit weather data that’s primarily used by pilots. The International Civil Aviation Organization (ICAO) ensures it is standardized throughout the world, although there are still some regional variations in the units used. You’ll see that METAR reports are given under the weather tab for airports on Flightradar24.

Once they get used to reading a METAR pilots can see all the relevant weather info for a given airfield at a glance. So in case you one day wish to become a pilot or are just hoping to one day impress a pilot, here’s a quick explanation of how to decode a METAR.

To start with, it might help to familiarize yourself with the Aviation Weather Center in the US. The agency provides a rich array of weather data to aviators and even for the non-pilot it can be interesting to take a look around at their data. It’s run by the National Oceanic and Atmospheric Administration, also known as NOAA, one of the most comprehensive sources for weather data in the world. Their graphical turbulence map of the US might be of particular interest to some. There’s plenty of other very detailed information, including various maps detailing forecasts for icing, winds and so on. If you’re an airman you can also go there to submit a PIREP, or “pilot report,” of actual weather conditions you’ve encountered. It’s also the place to go for METAR reports.

Decoding a METAR

Let’s take a look at the current METAR (at time of writing) for Honolulu (HNL). We simply input its ICAO airport code (PHNL), and if we select the “raw” METAR we get a line that looks like this:

PHNL 250953Z 05007G17KT 10SM FEW024 FEW040 27/19 A3001 RMK AO2 SLP163 T02670194 403220261

The key thing to know is that METAR reports, which can appear an indecipherable mess at first glance, always follow this pattern, and each block is set up to give information in as few characters as possible:

Place – Date and Time – Wind – Visibility – Phenomena – Clouds – Temperature – Pressure

You can cheat and have the AWC spit out a “decoded” version that translates this more or less into plain English. Flightradar24 also decodes the most relevant weather data and puts it at the head of every airport page on the site. It’s possible see the past 72 hours of METARs for most airports on the airport data pages.

However for the purposes of education, let’s stick with the raw info and go through piece by piece:

PHNL = the airfield, Honolulu’s Daniel K. Inouye International Airport. As mentioned this utilizes the ICAO code and not the more common three-letter IATA code (HNL). The two codes are sometimes similar, as they are in this case. However some ICAO codes are unrecognizable to those familiar with IATA codes.

250953Z = the date and time of the report. 25 in this case is the day of the month (today), and the time is 0953 Zulu time, also known as Greenwich Mean Time.

05007G17KT = the wind conditions. The 05007 means the wind is blowing from 050 degrees true at a speed of 07 knots, with gusts (indicated by the “G”) up to 17 knots. If the wind is inconsistent a VRB in place of the direction will indicate that it is “variable.” If there is little to no wind a “00000” will appear. The wind speed, by the way, is the mean wind speed in knots over the 10 minute period preceding the observation.

10SM = visibility. In the US, “statute miles” are used, so in this case the visibility is 10 statute miles (or higher). More commonly this will be expressed in meters, up to 9998. A reading of 9999 would indicate visibility of over 10 kilometers. A reading of 0000 indicates less than 50 meters visibility.

FEW024 / FEW040 = cloud cover. The FEW means what it sounds like – that there are few clouds. But for the weather nerds among us, FEW is defined as between 1 and 2 oktas (a unit of measure for amount of clouds). The number that follows indicates the height at which those clouds are found. So in this case, a few clouds at 2400 and 4000 feet above the airfield. You might also see SCT (scattered), BKN (broken) or OVC (overcast). CB or TCU would indicate convective cloud in the area. And here it’s good to know the term CAVOK, meaning cloud and visibility OK, which will be displayed when there is no significant weather in the vicinity and visibility is at 10km or more.

27/19 = the temperature and dewpoint. In this case the temperature is 27 degrees Celsius and the dewpoint is 19 degrees Celsius.

A3001 = the atmospheric pressure, a.k.a. altimeter setting. In the US this is expressed in Hg, so this would correspond to 30.01 inches of mercury (the A simply stands for “altimeter”). In other parts of the world this number will appear in mb or hP (hectopascals). This figure is used by pilots to ensure their altimeters display the correct altitude.

RMK AO2 SLP163 T02670194 403220261 = the add-ons, which can give a more complete picture of weather conditions but can also be a little more difficult to decipher, at least for a beginner. This part will require a little more memorization or keeping a guide handy to consult. But in this case, here’s what everything means:

RMK indicates “Remarks.”

A02 tells us it’s an automated station that has a precipitation sensor.

SLP163 tells us the “sea level pressure” is 1016.3 mb.

T02670194 is the hourly temperature and dewpoint in finer detail – in this case 26.7 Celsius and 19.4 Celsius respectively.

403220261 is the 24-hour maximum and minimum temperature, which is indicated by the ‘4’ at the beginning. The ‘0’ at digit two and digit six tells us the number is positive (for negative temperatures, the second and sixth digits would be ‘1’). So in this case: 32.2 and 26.1 Celsius respectively.

This is far from an exhaustive list of all codes used in METARs but it should take you pretty far in decoding this most important ones. For those of you that have made it this far, you might enjoy further reading at this guide to decoding METAR. That also includes the full table for decoding anything that might appear.

How long are METARs valid for?

METARs in the U.S. are valid for one hour and are issued hourly.

In other countries METARs are generally valid for 30 minutes and are issued twice per hour – at 20 minutes past the hour and 50 minutes past the hour.

Aviation Flight Categories

In the U.S. METARs can be shorted to display the time of flying that is possible at an airport with respect to ceiling and visibility. The four aviation flight categories are:

  1. VFR: Visibility greater than 5 miles and ceiling greater than 3000 feet.
  2. Marginal VFR: Visibility between 3 and 5 miles and/or a ceiling between 1000 feet and 3000 feet.
  3. IFR: Visibility of 1 mile of more but less than 3 miles and/or a ceiling of 500 feet or more but less than 1000 feet.
  4. Low IFR: Visibility less than 1 mile and/or a ceiling less than 500 feet.

Trend Type Forecast

A trend type forecast, or simply a “trend” is a forecast valid for two hours appended to a METAR or SPECI.

An example of a trend type forecast: TEMPO 3SM VCSH = Temporarily visibility of 3 statute miles, with showers in the vicinity (between 5 and 10 SM of the airport).

What are the differences between METARs and TAFs?

A METAR is Meteorological Terminal Air Report (or “aviation routine weather report”) is a weather report of a actual conditions at an airport at a specific time.

A TAF (Terminal Area Forecast) is a weather forecast for a given area around the airport specified in the forecast.

Therefore, the main difference between the two is that METARs are a record of actual conditions where TAFs are a prediction of future weather.

Another difference is that METARs may include a “remarks” (RMK) section. Remarks may include more accurate temperature, sea level pressure (SLP) or runway state group (for example if the runway is contaminated by snow).

TAFs, METARs and SPECIs use a common code to describe the weather such as TS for thunderstorms or SHRA for rain showers.