Understanding Aviation Weather
What Is a METAR?
A METAR is an aviation routine weather observation. It reports the conditions actually observed at an airport at a specific time — wind, visibility, present weather, cloud layers, temperature, dew point, and altimeter setting. Most stations issue a new METAR about once an hour, with special reports (SPECI) in between when conditions change significantly.
What Is a TAF?
A TAF is a terminal aerodrome forecast covering a specified period for an airport — commonly 24 or 30 hours. It describes the prevailing conditions expected within roughly five statute miles of the airport, along with forecast change groups that indicate when and how conditions are expected to change.
How to Read a METAR
Read a METAR group by group, left to right: report type and station, day-and-time in UTC (Z), wind (direction/speed, with gusts after a G), visibility in statute miles, present weather, sky condition (FEW/SCT/BKN/OVC with cloud base in hundreds of feet), temperature/dew point in Celsius, altimeter (A followed by inches of mercury), and finally the remarks after RMK.
How to Read a TAF
A TAF opens with the station, issue time, and valid period, followed by the initial prevailing conditions. Change groups modify the forecast: FM introduces a new set of prevailing conditions from a stated time, BECMG marks a gradual transition, TEMPO covers temporary fluctuations, and PROB30/PROB40 express the probability of the stated conditions. Temporary and probabilistic groups do not replace the prevailing forecast.
What Do VFR, MVFR, IFR, and LIFR Mean?
These flight categories summarize ceiling and visibility. VFR is a ceiling above 3,000 ft and visibility greater than 5 SM. MVFR is a ceiling of 1,000–3,000 ft or visibility 3–5 SM. IFR is a ceiling of 500–999 ft or visibility 1–3 SM. LIFR is a ceiling below 500 ft or visibility below 1 SM. The category is set by whichever of ceiling or visibility is more restrictive.
Why Weather Report Time Matters
Every METAR and TAF is tied to a specific time expressed in UTC (the Z time). A report only describes the conditions observed or forecast for that moment and place. As a report ages it becomes a weaker representation of the current situation, so always check the observation age and issue time before relying on a report.
METAR and TAF Limitations
Reports represent specified locations and times and are only part of a complete aviation weather briefing. Conditions can differ along a route, between reporting points, and after a report was issued. A decoder helps you understand a report — it does not replace an official preflight weather briefing or pilot-in-command judgment.