Met Office MAVIS USER GUIDES

How to decode a METAR

A Meteorological Aerodrome Report (METAR) follows a specific format, with each element providing specific information about weather conditions observed at an aerodrome.

An example METAR:

METAR COR EGLL 031020Z AUTO 07007KT 030V100 9999 NCD 12/08 Q1026 NOSIG=

Elements of the METAR

Identification

Report Type

Example: METAR

This indicates that the report is a routine Meteorological Aerodrome Report.

Example: SPECI

This indicates that the report is a Special Aeronautical Report, issued when there is a significant change in weather conditions.

Example: METAR COR

This indicates that the report is a corrected METAR, issued to correct a previous report.

Location

Example: EGLL

This is the ICAO code for the aerodrome where the report was made. In this case, EGLL is the code for London Heathrow Airport.

Date and Time

Example: 291020Z

This indicates the date and time of the report in UTC (Coordinated Universal Time). In this example, 29 is the day of the month, 1020 is the time in hours and minutes, and Z indicates that the time is in UTC.

Auto

Example: AUTO

This indicates that the METAR was fully automated with no human intervention.

AUTO METARs may only be disseminated when an aerodrome is closed or at H24 aerodromes, where the accredited Met observer is on a CAA approved overnight duty or break. Users are reminded that reports of visibility, present weather and cloud from automated systems should be treated with caution due to the limitations of the sensors themselves and the spatial area sampled by the sensors.

Wind

Wind Direction and Speed

Example: 31015G27KT

310 degrees, 15 knots, gusting to 27 knots.

Note: The Max wind gust is only given if it is 10 knots or more above the mean wind speed.

Variable Wind Direction

Example: 280V250

Varying between 280 and 250 degrees. This would be an extreme case of variable wind direction.

Note: Variable wind direction is given in a clockwise direction, but only when the mean speed is greater than 3 knots.

Visibility

Prevailing Visibility

Example: 3200

This indicates a prevailing visibility of 3200 metres.

Example: 0000

This indicates a prevailing visibility of less than 50 metres.

Example: 9999

This indicates a prevailing visibility of 10 kilometres or more.

Minimum visibility

Minimum visibility can be provided in a separate element of the METAR.

Example: 1200SW

This indicates a minimum visibility of 1200 metres in the south-west direction.

Note: The minimum visibility is only included alongside the prevailing visibility when the visibility in one direction (which is not the prevailing visibility) is less than 1500 metres or less than 50% of the prevailing visibility.

A direction is also included as one of the eight points of the compass (N, NE, E, SE, S, SW, W, NW).

Example: NDV

No directional variation in visibility. This is only available in AUTO METARs.

RVR (Runway Visual Range)

Example: R27R/1100

This indicates a runway visual range of 1100 metres on runway 27R.

Note: Runway visual range tendency can be added after the element. U indicates an increasing trend, D indicates a decreasing trend, and N indicates no change.

Example: R27R/1100D

The runway visual range on runway 27R is 1100 metres and decreasing.

Example: R24/0950V1100

The runway visual range on runway 24 is varying between 0950 and 1100 meters. Note that this range of values is only present in non-UK civil aerodromes.

Present Weather

Example: +SHRA

This indicates that there is heavy rain showers at the aerodrome.

Note: a plus sign (+) indicates heavy or developed weather, and a minus sign (-) indicates light weather. No additional qualifying symbol indicates moderate weather.

Weather Descriptors

Cloud

Example: FEW005 SCT010CB BKN025

This indicates that there are a few clouds at 500 feet, scattered cumulonimbus clouds at 1000 feet, and broken clouds at 2500 feet.

Cloud parameters

Cloud figures are given in hundreds of feet above the aerodrome level.

Cloud groups tend to be provided in groups of up to three, with the lowest cloud group given first. METARs may include more than three cloud groups, but this is not common.

CAVOK (Ceiling and Visibility OK)

This indicates that the visibility is 10 kilometres or more, there are no clouds below 5000 feet or below the highest minimum sector altitude, and there are no aviation significant to aviation.

Pronounced "Cav-oh-kay", this is an acronym for "Ceiling and Visibility OK".

Temperature and Dew Point

Example: 12/08

This indicates a temperature of 12 degrees Celsius and a dew point of 8 degrees Celsius.

If due point is missing, it would be reported as 10///.

M indicates a negative temperature or dew point.

QNH (Pressure on the subscale of the altimeter)

Example: Q0995

This indicates a QNH of 995 hPa (hectopascals).

If this value is prefixed with the letter A, it indicates a pressure in inches (inHg) and hundredths instead of hPa.

Example: A2992

This indicates a QNH of 29.92 inHg.

Recent Weather

Example: RETSRA

This indicates that there has been recent thunderstorm and rain.

This element uses the same weather descriptors as the present weather element, but is prefixed with RE to indicate that the weather occurred in the recent past.

Wind Shear

Wind sheer is not currently reported on UK civil aerodrome METARs.

Example: WS RWY24

This indicates that there is wind shear on runway 24.

Wind sheer is a sudden change in wind speed and or direction over a short distance.

Military Colour States

Military METAR reports also display a colour state BLU, WHT, GRN, YL01, YL02, AMB or RED, which are coded according to cloud base and visibility, whilst BLACK indicates the runway is unusable.

These thresholds are different to the colours used to display the observations on MAVIS. Click here to read more about the Visibility and Cloud Base Indicators used in MAVIS.

Example: WHT

This indicates a white colour state, which means that the weather conditions are good and there are no significant hazards.

Colour state codes

Runway State Group

Runway state groups are used to report the condition of the runway surface, including the presence of contaminants such as water, snow, or ice.

This is an 8-digit group that can be added to METARs from civilian aerodromes.

This group is presented in the format of DDCETTBB, where:

Example: 24421594

This indicates that runway 24 has a runway deposit code of 4 (dry snow), an extent of runway contamination code of 2 (between 11% and 25% of the runway surface contaminated), a depth of deposits code of 15 (15mm), and a friction coefficient code of 94 (Medium or Good)

Runway Designator

Runway Deposits

Extent of runway contamination

Depth of deposits

Friction coefficient

Reported as the mean friction coefficient multiplied by 100 or as Breaking Action code.

If the equipment used does not measure friction accurately in the given weather conditions, such as slush or snow, the breaking action may be reported as 99 to indicate that the figures are unreliable. If the breaking action is not reported, it may be because the aerodrome is closed or the runway is not operational.

Trend

The trend element is used to provide a forecast of the weather conditions at the aerodrome for the next two hours.

Any of the wind, visibility, weather or cloud groups may be used, and CAVOK. Multiple groups may be used in a single trend element.

Example: BECMG FM1100 23035G50KT 3000 SHRA

This indicates that the weather conditions are expected to become worse from 1100 UTC, with a wind from 230 degrees at 35 knots gusting to 50 knots, a visibility of 3000 metres, and rain showers.

Trend indicators

Examples

EGGY 301220 METAR EGLY 301220Z 24015KT 200V280 8000 —RA FEW010 BKN025 18/15 Q0983 TEMPO 3000 RA BKN008=

EGLY: Issued at 1220Z on 30th. Surface wind: mean 240 deg true, 15 KT; varying between 200 and 280 deg; Prevailing vis 8 km; light rain; cloud; 1-2 oktas base 1000 ft , 5-7 oktas 2500 ft; temperature +18°C, dew point +15°C QNH 983 hPa; Trend: temporarily 3000 m in moderate rain with 5-7 oktas 800 ft.

EGGY 301220 METAR EGPZ 301220Z 30025G37KT 270V360 6000 1200NE +SHSN SCT005 BKN010CB 03/M01 Q0999 RETS BECMG AT1300 9999 NSW SCT015=

EGPZ: Issued at 1220Z on the 30th. Surface wind: mean 300 deg true, 25 KT; maximum 37 KT, varying between 270 and 360 deg; prevailing vis 6 km, minimum vis 1200 m (to north-east); heavy shower of snow, Cloud; 3-4 oktas base 500 ft , 5-7 oktas CB base 1000 ft, temperature +3°C, dew point -1°C; QNH 999 hPa; Thunderstorm since the previous report; Trend: improving at 1300 UTC to 10 km or more, nil significant weather, 3-4 oktas 1500 ft.