Aviation Weather,
METAR & TAF Decoder

A METAR (Meteorological Aerodrome Report) is a standardised weather observation report for an airport, issued hourly or when significant weather changes occur (SPECI). METARs follow an ICAO-defined format and are read left to right: station identifier, observation time in Zulu, wind direction and speed, visibility, weather phenomena, cloud layers, temperature/dew point, and altimeter setting. This decoder translates every coded element into plain English automatically.

A TAF (Terminal Aerodrome Forecast) predicts weather conditions at an airport for the next 24 to 30 hours. While a METAR reports what the weather is right now based on observation, a TAF forecasts what the weather will be. TAFs use similar codes to METARs but add change groups (FM, TEMPO, BECMG, PROB30/40) to describe expected transitions between weather conditions over time. Not all airports issue TAFs typically only airports with instrument approaches and traffic levels warranting a dedicated forecast.

Flight categories classify airport weather conditions by ceiling and visibility. VFR (Visual Flight Rules) means ceiling above 3,000 feet and visibility over 5 statute miles. MVFR (Marginal VFR) is ceiling 1,000–3,000 ft or visibility 3–5 SM. IFR (Instrument Flight Rules) is ceiling 500–999 ft or visibility 1–3 SM. LIFR (Low IFR) is ceiling below 500 ft or visibility below 1 SM. These categories determine the minimum pilot qualifications and equipment required for flight in those conditions.

Crosswind component is calculated using the formula: crosswind = wind speed × sin(wind direction - runway heading). This decoder calculates it automatically for each runway. For example, if wind is 270° at 20 knots and the runway heading is 240°, the angle difference is 30°, giving a crosswind of 20 × sin(30°) = 10 knots. Positive headwind values indicate headwind; negative values indicate tailwind. Always compare the result to your aircraft's demonstrated crosswind component and your personal limits.

Density altitude is the pressure altitude corrected for non-standard temperature. It represents the altitude at which the aircraft 'thinks' it is flying in terms of air density. High density altitude reduces engine power, propeller efficiency, and lift resulting in longer takeoff rolls, reduced climb rates, and higher approach speeds. It is calculated from station elevation, current altimeter setting, and temperature. Pilots should calculate density altitude before any takeoff or landing at high-elevation or hot-weather airports.

Standard METAR observations (METAR) are typically issued once per hour, at approximately 50–55 minutes past the hour at most airports. Special observations (SPECI) are issued immediately when significant weather changes occur, such as ceiling or visibility crossing flight category boundaries, onset or cessation of thunderstorms or freezing precipitation, or a wind direction change of 45 degrees or more with speed above 10 knots. This tool fetches the most recent observation available from the NOAA data server.

QNH is the atmospheric pressure adjusted to sea level, used to set the aircraft altimeter so that it reads the correct altitude above mean sea level. It is reported in hectopascals (hPa) in most of the world (e.g. Q1013) and in inches of mercury (inHg) in the United States (e.g. A2992). Both represent the same measurement in different units. This decoder displays both: hPa for ICAO standard and inHg for US operations. Setting the correct QNH is essential for terrain clearance and maintaining vertical separation between aircraft.

This tool is designed for quick weather checks, pre-flight briefing, and METAR/TAF decoding. It provides real-time data from official NOAA sources and calculates useful derived values like density altitude and crosswind components. However, it should complement not replace a complete weather briefing from your national meteorological authority. For flight planning, always check the full weather picture including SIGMETs, AIRMETs, winds aloft, PIREPs, and significant weather charts through your flight planning service or aviation weather provider.

TAFs are produced by human forecasters (or specialized automated systems) and are only issued for airports that have sufficient traffic and infrastructure to warrant a dedicated terminal forecast. Small general aviation airfields, private strips, and airports without instrument approach procedures typically do not have TAFs. In these cases, use the METAR for current conditions and check area forecasts (GFA/FA), MOS forecasts, or the nearest airport with a TAF for the expected conditions in your region.