METAR Decoder

A METAR is a sentence with the vowels taken out. It was shaped to fit a teleprinter line, and it still reads like one: fixed-width groups, no punctuation to speak of, and a meaning that shifts with the country the report came from. This page walks the groups in the order the handbooks lay them down, names each one in English, and — the part that matters — tells you which groups it did not understand instead of quietly skipping them. It reads both dialects: metres and 9999 for visibility as well as statute miles and fractions, and both Q for hectopascals and A for inches of mercury. Nothing is fetched and nothing is uploaded; the report you paste is decoded in this page.

How it is calculated

CCCC YYGGggZ [AUTO] dddff(Gfm fm)KT [dnV dx] VVVV w'w' NsNsNshshshs T'T'/T'dT'd QPHPHPHPH

The body of a METAR is a fixed sequence of groups: station, date and time, report modifier, wind, visibility, runway visual range, present weather, sky condition, temperature and dew point, then the altimeter. The order never varies, which is what makes the code readable at all — but any group can be missing, because the handbook says that when an element does not occur or cannot be observed, the corresponding group and the space before it are left out of that report. So a decoder cannot count positions; it has to try each group against the rules that are still ahead of it, and say so when a group matches none of them.

Source: Federal Meteorological Handbook No. 1, FCM-H1-1995, paragraph 12.6.8, Table 12-2 — "The weather groups shall be constructed by considering columns 1 to 5 in the table above in sequence, i.e., intensity followed by description followed by weather phenomena, e.g., heavy rain shower(s) is coded as +SHRA"

Questions people ask

Why does the pressure look different in American and European reports?

Because they are two different groups. A leading Q means the QNH is in whole hectopascals, so Q1013 is 1013 hPa. A leading A means inches of mercury written without its decimal point, using tens, units, tenths and hundredths, so A2992 is 29.92 inHg. This page reads both and prints back the one the report actually carried rather than converting between them.

Is the visibility in metres or in miles?

Whichever the station used, and the code says which. A bare four-figure group is metres, where 9999 means ten kilometres or more and 0000 means less than fifty metres. A group ending in SM is statute miles, and there a whole number and its fraction are written with a space between them, so 1 1/2SM arrives as two groups and is put back together here. M in front means below the lowest reportable value, P means above the highest.

How is a weather group like -SHRA built up?

In layers, read left to right: intensity or proximity, then a descriptor, then the phenomena. A minus is light, a plus is heavy, and no symbol at all means moderate — the absence is the code. VC is not an intensity but a place: in the vicinity rather than at the field. So -SHRA is a light shower of rain, TSRA a thunderstorm with rain, and VCTS a thunderstorm somewhere nearby.

What happens to the remarks after RMK?

They are shown to you whole and marked as not decoded. Everything after RMK is a second code with its own rules — sea level pressure, peak wind, precipitation totals, sensor status — much of it specific to American automated stations. Printing it back untouched is honest; guessing at it would not be, and dropping it would hide the half of the report an observer often cared most about.

What will it not decode?

Anything this page has not read a definition for, and it says so by name. Wind speeds in metres per second, runway state groups, military colour states, the BECMG and TEMPO trend forecasts and the whole of the remarks section are listed rather than interpreted. A decoder that guesses at a group is worse than one that admits it does not know, because you cannot tell the two apart from the output.

Does it fetch the current weather for an airport?

No. There is no network call here at all. You bring the report — from an aviation weather service, a briefing pack or a printout — and this page turns it into English. That also means it works on an old report, on a made-up one, and with no connection.

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