• CHI Aerospace

How to read a METAR

Updated: Aug 4, 2019

What is a METAR you may ask? How do I read one? A METAR is an Aviation Routine Weather Report (METAR). It is a surface weather observation in the terminal area of the airport used to inform pilots of the local weather phenomena. It is generally published hourly, usually 55 or 56 minutes past the hour, and contains the following information:

- Type of Report

- Station identifier

- Date and time of report

- Report modifier (As required)

- Wind

- Visibility

- Present Weather Group

- Sky Condition

- Temperature/Dewpoint

- Altimeter

- Remarks

- Automated, Manual, and Plain Language Remarks

- Sensor Status Indicators

How to find the METAR:

Go to https://www.aviationweather.gov/metar and select the airport you’re flying out of.

An example of a METAR can be seen below:

1. Type of Report (METAR) As seen here, METAR is the type of report. This indicator precedes the body of all reports, but may not be shown or displayed on all aviation weather sites. There are two types of reports - a METAR or a SPECI. A METAR is the scheduled observation usually 55-56 minutes past the hour. A SPECI is a report that is given between the usual intervals of the METAR that contain significant weather changes such as major thunderstorms or tornadoes.

2. Station Identifier (KPSM) The station identifier is shown in ICAO (International Civil Aviation Organization) format and is included in all reports to identify the station to which the code report applies. KPSM is the airport code for Portsmouth, NH.

3. Date and Time (161556Z)

The date and time are coded in all reports in the following format:

The day of the month in the first two digits (16); followed by the hour (15); and the minutes (56) in UTC or “Zulu” (Z) time.

16 (16th day of the month)

1556Z (15:56 UTC)

4. Report Modifier (AUTO) This identifies the METAR/SPECI as a fully-automated report with no human intervention or oversight. In this case, the report was fully-automated. In the event of a corrected report, you will see “COR” instead of “AUTO.”

5. Wind (09008G12KT)

The wind information is grouped into three categories: wind direction (degrees); wind speed (knots), and wind gusts (knots).

Wind direction - coded as the first three digits (090), determined by averaging the recorded wind direction over a 2-minute period. It is coded as tens of degrees relative to true north. Directions less than 100 degrees are preceded with a 0. For example, a wind direction of 90 degrees is coded as 090. A wind from the north is coded as 360.

09008G12KT (090 is the wind direction)

Wind direction may be considered variable when, during the previous 2-minute evaluation period, the wind speed was 6kts or less. In this case the wind may be coded as VRB in place of the three-digit wind direction.

Wind speed - coded as two or three digits (08) immediately follows the wind direction. Wind speed is determined by averaging the speed over a 2-minute period and is coded in whole knots (kts). If wind speed is less than 10 kts, a leading 0 is used to maintain a two-digit wind code format, like in this example.

09008G12KT (08 is the wind speed in knots)

If no motion of air is detected, the air is reported as “calm.” A calm wind is displayed like “00000KT.”

Wind gusts - coded in two or three digits following the wind speed. The “G” signifies that there are wind gusts, and the number value signifies the speed of wind gusts in knots (“KT”).

09008G12KT (wind gusts at 12 knots)

6. Visibility (10SM)

Visibility is coded as the surface visibility in statute miles. The visibility group ends with “SM” to reference statute miles.

10SM = 10 statute miles of visibility

You may also see visibility look something like...

1 1/2SM = 1 and a ½ statute miles of visibility (here, the space separates whole number from a fraction)

M1/4SM = less than ¼ statute miles of visibility

(here, the preceding “M” means “less than”)

7. Present Weather (+RA) Present weather includes precipitation, obscurations and other weather phenomena. See table 3-2 below for weather codes.

In this case, +RA = heavy rain.

8. Sky condition (BKN050)

This is a description of the sky’s appearance. It includes either cloud cover, vertical visibility, or clear skies. The first three letters characterize the clouds with amount of cloud coverage (BKN) which means “broken clouds.” The numbers describe the base of the clouds in hundreds of feet.

BKN050 = broken clouds at 5000’

Vertical visibility (VV) is the distance seen from the ground up. You will find vertical visibility listed when it’s rather foggy and difficult to see the base of the “cloud.”

The ceiling is 500 ft in both examples, but the indefinite ceiling example (bottom) produces a more adverse impact to landing aircraft. This is because an obscuration (e.g. fog, blowing dust, snow) limits runway acquisition due to reduced slant range visibility. This pilot would be able to see the ground, but not the runway. If the pilot was at approach minimums, the approach could not be continued and a missed approach must be executed.

9. Temperature / Dewpoint (16/06) These numbers describe the temperature and dew point in degrees Celsius. Temperature is the first number (16) and is the degree of hotness or coldness of the ambient air, as measured by a suitable instrument.

Dewpoint is the second number (06) and is the temperature to which a given parcel of air must be cooled at constant pressure and constant water vapor content for the air to become fully saturated.

Temperature and dewpoint are displayed as two digits, rounded to the nearest whole degree Celsius. If the number is less than 10, a zero is placed before the temperature number to maintain a two digit number. Sub-zero temperatures and dewpoints are prefixed with an M.

16/06 (16 is the temperature in degrees Celsius)

16/06 (06 is the dew point in degrees Celsius)

10. Altimeter (A2980)

This is the altimeter setting group, which codes the current pressure at elevation. This setting is used by aircraft altimeters to determine true altitude above a fixed plane of mean sea level (MSL). The altimeter always starts with an “A” and is followed by the four-digit group representing the pressure in tens, units, tenths, hundredths of inches of mercury. Decimal point is not coded.

11. Remarks (RMK)

Remarks are separated from the body of the report by the contraction “RMK.” When no remarks are necessary, RMK is not required. There are many different types of remarks, however this article will review more of the common remarks seen.

11.1. Type of Automated Station (AO2A)

There are two types of automated stations - AO1 or AO2. AO2 is an automated station which has a precipitation discriminator, meaning it allows differentiation of precipitation (snow, hail, rain, etc.). AO1 is an automated station which does not have a precipitation discriminator, therefore it cannot distinguish types of precipitation.

In this case, the automated station (AO2A) has a precipitation discriminator and identified the precipitation as rain.

11.2. Sea Level Pressure (SLP132)

At designated stations, sea level pressure is coded in the following format:

SLP as the identifier, immediately followed by sea level pressure in millibars.

The hundreds and thousands units are not coded and must be inferred.

SLP132 = sea level pressure

SLP132 = 1,013.2 mb

More examples:

A sea level pressure of 998.2 mb is coded as SLP982

A sea level pressure of 1,013.2 mb is coded as SLP132.

11.3. Hourly Temperature and Dewpoint (T01561055)

At specific stations, the hourly temperature and dewpoint group are further coded to the tenth of a degree Celcius. This code starts with “T” followed by a series of eight numbers, the first being temperature, and the last four being the dewpoint. The first number may be a 1 or a 0. A 1 indicates the temperature or dewpoint is negative whereas a 0 indicates the temperature or dewpoint is positive. The following two numbers is the whole degree of either the temperature (15) or dewpoint (05). The last number of the four digits is the tenth of degree (Temperature 6 and dewpoint 5).

T01561055 would be read as “The temperature is positive 15.6 degrees Celsius and the Dewpoint is negative 5.5 degress Celsius.

12. Maintenance Indicator ($)

This is coded when automated systems detect that maintenance is needed on the system.


Recent Posts

See All