Every pre-duty brief starts with the same question: what is the weather doing now, and what is it going to do? METARs and TAFs answer it. Flight categories turn those reports into something you can read in a second.
METAR: what's happening now
A METAR is a routine surface observation, usually issued every hour, with special reports (SPECI) when conditions change significantly. It gives wind, visibility, present weather, sky condition, temperature and dew point, and altimeter setting.
- Watch the temperature and dew point spread. When they converge, especially overnight, fog and low ceilings become more likely.
- Check the time. A METAR is a snapshot. One that's 50 minutes old during a fast-moving change may already be out of date.
TAF: what's expected
A Terminal Aerodrome Forecast covers about five statute miles around an airport, typically for 24 or 30 hours. Read the change groups carefully:
- FM (from): a lasting change starting at a specific time.
- TEMPO: temporary fluctuations expected for less than half of the period stated.
- PROB30 / PROB40: the probability of conditions occurring during the period.
Flight categories
Flight categories summarize ceiling and visibility. The lower of the two decides the category:
- VFR: ceiling above 3,000 ft AGL and visibility above 5 statute miles.
- MVFR (marginal VFR): ceiling 1,000 to 3,000 ft and/or visibility 3 to 5 miles.
- IFR: ceiling 500 to below 1,000 ft and/or visibility 1 to below 3 miles.
- LIFR (low IFR): ceiling below 500 ft and/or visibility below 1 mile.
Categories are a fast summary, not a substitute for your program's minimums, which may be stricter, especially at night or in mountainous terrain.
Beyond the airport
METARs and TAFs describe airports. The air between them is covered by area products: AIRMETs (moderate icing, turbulence, IFR conditions and mountain obscuration), SIGMETs (severe or extreme hazards, including convective SIGMETs), and Center Weather Advisories for short-term hazards. A brief that checks only airports can miss what's in between.
BRIEFED pulls METARs, TAFs, AIRMETs, SIGMETs and CWAs from the National Weather Service Aviation Weather Center and shows each airport's flight category on the brief and on a map.