UK METAR Decoder
Paste a UK METAR or type an EGxx code. Metric units and trend groups decoded.
Accepts any UK or European METAR, an ICAO code like EGLL, or an airport name.
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What changes in a UK METAR
The structure is identical to a US report. The order of the groups never varies and the cloud and weather codes are the same. What changes is the units, and that is where the mistakes happen.
Pressure is a Q-group in whole hectopascals. Q1015 is 1015 hectopascals, and there is no decimal point to put back. A US report would write the same pressure as an A-group in inches, so A2997.
Visibility is in metres, given as four digits. 9999 means ten kilometres or more and is the top of the scale. Below that the digits are literal, so 4000 is four kilometres and 0800 is 800 metres.
CAVOK and trend groups
CAVOK replaces the visibility, weather and cloud groups all at once. It needs ten kilometres or more, no cloud below 5000 feet or the minimum sector altitude, no convective cloud at any height, and no significant weather.
It is not clear sky. A field can report CAVOK with a solid overcast at 8000 feet, and with strong gusting wind, because wind lives in its own group. The CAVOK against 9999 comparison works through what each one actually promises.
UK reports usually end with a trend group rather than the long remarks section a US report carries. NOSIG means no significant change is expected in the next two hours. Where a change is expected, the trend uses BECMG or TEMPO with a time.
Colour states at military aerodromes
UK military fields add a colour state, a single word summing up the ceiling and visibility together. It runs from blue and white at the good end through green, yellow and amber, down to red and black.
Treat it as briefing shorthand rather than a replacement for the numbers. The ceiling and visibility groups in the body are still the authoritative values, and the colour is a fast way to say roughly where they sit.
The full table is on the military aviation weather page, alongside the numeric icing and turbulence groups a military TAF carries.
The altimeter trap worth ten minutes
An altimeter set wrong reads the wrong height by about 30 feet per hectopascal. On a low pressure day that is not a rounding error.
A field reporting Q0985 and a pilot dialling 29.85 inches have a 26 hectopascal gap between them, which puts the altimeter about 780 feet high and the aircraft 780 feet low. On approach, in cloud, that is the whole hazard.
The other half of the problem is the transition altitude, which in the UK is often 3000 to 6000 feet and varies by airport rather than being a fixed 18,000. Read it off the plate before you need it. The A2992 against Q1013 comparison covers the conversion.
Frequently asked questions
Does this decode UK METARs correctly?
Yes. Hectopascal Q-groups, four-digit visibility in metres, CAVOK and the NOSIG, BECMG and TEMPO trend groups are all read, alongside the US conventions. The same engine handles both.
What does Q1015 mean?
An altimeter setting of 1015 hectopascals. There is no hidden decimal point, unlike a US A-group where A2992 means 29.92 inches of mercury. Both describe the same kind of setting, QNH.
What does 9999 mean in a UK METAR?
Visibility of ten kilometres or more. It is the top of the metric scale, so anything better is still written 9999. Lower values are read literally, so 0800 is 800 metres.
Why do UK reports not have a long remarks section?
Sea-level pressure groups, tenth-of-a-degree temperatures and hourly precipitation are US conventions. UK reports use a trend group instead, which is a short forecast for the next two hours.
What is a colour state?
A one-word ceiling and visibility summary used at military aerodromes, from blue and white through green, yellow and amber to red and black. It is shorthand for briefing, not a replacement for the groups.