How to Read an Airport METAR: VFR, IFR and What They Mean for Delays
A METAR is the standard hourly weather observation from an airport. Pilots and air traffic controllers use it to plan arrivals and departures. A few pieces of it help travelers guess whether weather could slow their flight.
The flight category
Aviation weather services summarize each METAR as a flight category. VFR (visual flight rules) means cloud base above 3,000 feet and visibility above 5 miles. MVFR (marginal) is cloud base between 1,000 and 3,000 feet or visibility 3 to 5 miles. IFR (instrument) is cloud base between 500 and 1,000 feet or visibility 1 to 3 miles. LIFR (low instrument) is below those limits.
Most large airports operate normally in IFR because aircraft and runways are equipped for it, but they usually reduce the number of arrivals per hour, which is how delays begin.
Reading the raw report
A METAR starts with the airport code and the day and time in UTC. Wind appears as direction and speed in knots, for example 27012KT is wind from 270 degrees at 12 knots. Visibility follows in statute miles. Cloud layers are listed with their height in hundreds of feet, so BKN008 is a broken layer at 800 feet.
Temperature and dew point are in degrees Celsius. When they are within a few degrees of each other, fog or low cloud becomes more likely. The altimeter setting follows and a TAF is the matching forecast.
Wind and runways
Strong crosswinds, gusts and thunderstorms near the field can limit which runways an airport can use. A change in wind direction can trigger a runway configuration change, which temporarily slows traffic.
Using it as a traveler
If your arrival or departure airport is showing IFR or LIFR, check the FAA delay status and your airline before you leave. If it is VFR with no FAA programs, weather is unlikely to be the reason for a delay.