Aviation weather: METAR and TAF decoder

For learning and situational awareness. It is not an official briefing: before you fly, get one from your flight service / AIS (in the US, 1800wxbrief.com or an approved provider).

How to use it

Live reports — type ICAO station codes (KSFO, EGLL) and press Get reports, or Airports near me to use your location (asked once, used only in this page) to pick the nearest airports from the bundled airport list. Each station shows its METAR and TAF decoded, with the source that answered.
Decode — paste any METARs and TAFs (several at once; TAF continuation lines are joined) or pick an example. Nothing is fetched.
Reference — the flight-category table and the weather and cloud codes.

Every decoded METAR has a Crosswind and density altitude box. Pick a runway (from the airport data when the station is in it, or type 28R or a heading such as 284) for the headwind or tailwind and crosswind components, including gusts. The field elevation (filled from the airport data or the source when known) gives the pressure altitude and the density altitude.

Where the reports come from

aviationweather.gov Data API (NOAA Aviation Weather Center) — worldwide METARs and TAFs. In October 2026 it sends no CORS header, so a web page on another site cannot read it and the browser blocks the reply. The tool therefore does not ask it directly unless you tick Try aviationweather.gov directly (to check whether that has changed).
The gitwebsite app — if the gitwebsite app (or gw serve) runs on your computer, its companion relays aviationweather.gov for every station, US or not; the tool asks it first. In the app’s preview it is used at once; from this site press ⚡ Use the gitwebsite app and approve the code in the app.
Your relay — not needed if the gitwebsite app is running; otherwise, if you run the small local relay described in the flight tracker's help, enter its URL (for example http://127.0.0.1:8099/awc) under Relay URL; the tool then asks <relay>/api/data/metar?ids=…&format=json and …/taf?…. Chrome and Firefox allow an https page to call http://127.0.0.1; Safari does not. This is the way to get stations outside the US live.
api.weather.gov (US National Weather Service) — sends CORS headers, so it works straight from the page, but only for US stations (K…, P…, TJ…). The METAR is the newest observation that carries the raw report; the TAF is the latest NWS TAF product for the station.
Otherwise, paste the report on the Decode tab.

What is decoded

METAR/SPECI: COR, AUTO; wind in KT, MPS or KMH, VRB, calm, gusts, variable sector (210V280); visibility in statute miles with fractions (1 1/2SM, M1/4SM, P6SM), in metres (9999, 0350, 4000 1500NE, NDV), CAVOK; RVR (R28L/1600VP6000FT, R27L/0550U); present and recent weather with intensity, proximity (VC), descriptors and phenomena; cloud layers with CB/TCU, VV, SKC, CLR, NSC, NCD; temperature/dew point (with M for minus); altimeter A (inHg) or Q (hPa); wind shear; NOSIG, BECMG, TEMPO trends.
US remarks: AO1/AO2, SLP, the T group (temperature to 0.1 °C, used for the calculations), 6- and 24-hour max/min (1, 2, 4 groups), pressure tendency (5 group), precipitation (P, 6, 7), peak wind, begin/end times (RAB15E30), and sensor flags ($, TSNO, PNO, RVRNO). Anything not decoded is shown as written.
TAF: AMD/COR, issue time, validity, FM, BECMG, TEMPO, PROB30/PROB40 (with or without TEMPO), TX/TN, NSW, and a timeline of the forecast flight category. A BECMG group changes the prevailing conditions for the rest of the forecast; TEMPO and PROB groups are drawn as their own rows, combined with the prevailing conditions they modify.

The numbers

Flight category (as on aviationweather.gov): VFR ceiling above 3,000 ft and visibility over 5 SM; MVFR ceiling 1,000–3,000 ft and/or visibility 3–5 SM; IFR ceiling 500 to below 1,000 ft and/or 1 to below 3 SM; LIFR below 500 ft and/or below 1 SM. The ceiling is the lowest broken, overcast or vertical-visibility layer. These are not your airspace’s legal VFR minimums.
Crosswind = wind × sin(angle between wind and runway), headwind = wind × cos(angle). METAR and TAF winds are true; runway numbers are magnetic — where the airport data gives the runway’s true heading it is used, otherwise the runway number, and the difference is the local magnetic variation.
Pressure altitude from the altimeter setting and field elevation by the ISA relation (the rule of thumb, elevation + 1,000 ft per inHg below 29.92, is shown alongside).
Density altitude: the altitude in the standard atmosphere with the same air density, computed from station pressure and temperature, with humidity through the virtual temperature — the NWS formula DA = 145,442 × (1 − (ρ/ρ₀)^0.235) ft. The FAA rule of thumb PA + 118.8 × (OAT − ISA) (Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25, ch. 4) is shown alongside.
Relative humidity by the Magnus formula (Alduchov and Eskridge, 1996).

The parser tests use real reports from aviationweather.gov and the NWS plus the formats in the FAA Aviation Weather Handbook (FAA-H-8083-28).

Limits

Live data outside the US needs the gitwebsite app, the relay or a paste (see above). The NWS API carries US stations only, and its newest few observations sometimes lack the raw report, so the METAR shown can be up to an hour older than aviationweather.gov’s.
The decoder follows the WMO/ICAO code and US FMH-1 practice. National variants (e.g. Canadian remarks, military colour states, runway-state groups) are shown undecoded rather than guessed.
TAF times are day-of-month and UTC; the timeline assumes the forecast stays within a month rollover of 31 days.
Not a substitute for an official weather briefing, NOTAMs, or your aircraft’s performance charts.

Linking to an example

Settings have short parameters and the tab comes from the # part of the address, for example /tools/aviation-weather/?ids=KSFOor ?metar=KSFO%20150056Z%2030010KT…&rwy=28R.











Tab
Parameter
Meaning
Example




#live
ids
station codes, comma-separated (fetched when the tab opens)
ids=KSFO,KOAK


#decode
metar, taf
a report to decode (URL-encoded; several METARs separated by %0A)
metar=EGLL%20151020Z%2024012KT%20CAVOK%2018%2F09%20Q1021


both
rwy
runway or heading for the crosswind
rwy=28R


both
elev
field elevation in feet (for density altitude)
elev=5434


all
units
us or metric for heights and distances
units=metric



example
one of the presets below (it also picks the tab); other parameters override it
example=fog-lifr




The relay URL is never put in a link.


Presets:




ksfo-clear — San Francisco on a clear evening (US format)


egll-cavok — London Heathrow, CAVOK (ICAO format)


fog-lifr — fog: quarter-mile visibility, RVR, and an indefinite ceiling — LIFR


thunderstorm — thunderstorm with heavy rain, gusts and remarks (Dallas/Fort Worth)


hot-and-high — density altitude: Denver on a hot afternoon


egll-taf — Heathrow TAF with TEMPO, PROB30/40 and BECMG groups


kjfk-taf — New York JFK TAF with FM groups


live-sfo-lhr — fetch live reports for San Francisco and Heathrow