METAR KJFK 041253Z 27015G25KT 10SM FEW250 18/06 A3012 RMK AO2. That string of letters and numbers looks like someone fell asleep on a keyboard. But to a pilot, it’s a complete weather picture in 15 seconds flat — wind, visibility, clouds, temperature, and pressure, all encoded in a format that hasn’t fundamentally changed since the 1960s.

Every flight begins with a METAR. Student pilots learn to decode them in their first weeks of ground school. Airline dispatchers build flight plans around them. Air traffic controllers use them to set approach procedures. If you’ve ever wondered what pilots are actually reading when they check the weather before a flight, this is it. And it takes about five minutes to learn.

Let’s break that JFK example apart, piece by piece.

Station and Time

KJFK is the ICAO airport identifier. The “K” prefix means it’s in the contiguous United States. EGLL is London Heathrow. LFPG is Paris Charles de Gaulle. Every airport on the planet has a four-letter code, and it’s always the first thing in the METAR.

041253Z tells you when the observation was taken. The 04th day of the month, at 1253 Zulu time. “Zulu” means UTC — Coordinated Universal Time — which aviation uses worldwide to avoid confusion between time zones. A pilot in Tokyo and a controller in New York are both looking at the same clock.

Wind: Direction, Speed, and Gusts

27015G25KT is the wind. The first three digits (270) are the direction the wind is coming from, in degrees from true north. 270 degrees means the wind blows from the west. The next two digits (15) are the sustained speed in knots. G25 means gusts to 25 knots. KT confirms the units are knots.

This one line drives landing decisions. A 270-degree wind at 15 knots gusting 25 means a crosswind component on any runway that doesn’t face roughly east-west. Pilots instantly calculate whether the crosswind exceeds their aircraft’s limits — or their own comfort level. A gusty crosswind is the single most common reason for go-arounds and diversions at airports worldwide.

Variable winds get reported too. If the wind direction fluctuates widely, you’ll see something like VRB05KT (variable at 5 knots) or 27015G25KT 240V310 — meaning the direction varies between 240 and 310 degrees. Light and variable winds are a pilot’s friend. Strong and gusty winds are a puzzle to solve.

Visibility and Weather

10SM means 10 statute miles of visibility — essentially clear conditions where you can see as far as matters. In the US, visibility is reported in statute miles. Most of the rest of the world uses metres: 9999 means visibility of 10 km or more (the maximum reported).

When weather is present, it appears between visibility and clouds. The codes are intuitive once you know the system: RA is rain. SN is snow. FG is fog. TS is thunderstorm. BR is mist. A minus sign (-) means light, a plus sign (+) means heavy. So +TSRA means heavy thunderstorms with rain — the kind of weather that grounds flights and sends pilots to the crew lounge for coffee.

The combination codes can get dramatic. FZRA is freezing rain — one of the most dangerous conditions in aviation. BLSN is blowing snow. +FC is a funnel cloud or tornado. Each code tells the pilot exactly what’s happening between them and the ground, without ambiguity, without interpretation, and without language barriers. A Japanese pilot reads +TSRA the same way a Brazilian pilot does.

Clouds, Temperature, and Pressure

FEW250 describes the cloud layers. FEW means 1–2 eighths of the sky is covered — scattered wisps at 25,000 feet. The hierarchy runs: FEW (few), SCT (scattered, 3–4 eighths), BKN (broken, 5–7 eighths), OVC (overcast, 8 eighths — complete cover). The number is the cloud base in hundreds of feet above ground level. BKN015 means a broken layer at 1,500 feet — low enough to require an instrument approach at most airports.

18/06 is temperature and dewpoint in Celsius. The gap between them tells an experienced pilot a lot: a wide spread (like 18/06) means dry air and good visibility. A narrow spread (like 18/16) means the air is saturated and fog or low clouds are likely. When temperature and dewpoint meet, fog forms. Pilots watch that spread like a hawk during evening flights.

A3012 is the altimeter setting — the atmospheric pressure that calibrates the aircraft’s altitude instruments. In the US, it’s expressed in inches of mercury (30.12 inHg here). Most of the world uses hectopascals: Q1020. Setting the wrong altimeter is a potentially fatal error — your instruments will show you at the correct altitude when you’re actually higher or lower. It’s one of the first things a pilot reads and sets on every approach.

Five Minutes, One Skill for Life

That’s it. Station, time, wind, visibility, weather, clouds, temperature, pressure. Once you know the format, you can decode any METAR on the planet in seconds. Pull one up right now — search “METAR” followed by any airport code — and try it yourself. You’ll never look at an airport weather forecast the same way again.

Pilots live and die by these reports. Literally. A METAR that shows deteriorating visibility and a closing temperature-dewpoint spread is a warning that conditions are about to change. A sudden wind shift with gusts might mean a frontal passage. Thunderstorms in the remarks section mean rerouting. It’s the most important weather format in aviation, and now you can read it too.

Sources: Federal Aviation Administration, International Civil Aviation Organization, Boldmethod, NOAA Aviation Weather Center