What is a METAR?
METAR stands for Meteorological Aerodrome Report (from the French "Météorologique Aviation Régulière"). It is a standardized format for reporting current surface weather conditions at an airport. METARs are generated by Automated Surface Observing Systems (ASOS) or Automated Weather Observing Systems (AWOS) and are issued every hour, typically between 50-59 minutes past the hour.
When conditions change significantly between regular observations — such as a sudden drop in visibility or wind shift — a Special METAR (SPECI) is issued. These unscheduled reports use the same format but are triggered by specific criteria defined in the Federal Meteorological Handbook.
METARs are the primary tool for evaluating current conditions at a departure, en-route, or destination airport. Every preflight weather briefing should include current METARs for all relevant airports along your route.
METAR format breakdown
A METAR follows a strict sequence. Here is a real-world example decoded field by field:
METAR KJFK 161853Z 31015G25KT 10SM FEW040 SCT080 BKN250 22/12 A3002 RMK AO2 SLP168 T02220122
- METAR — Report type (METAR for routine, SPECI for special)
- KJFK — ICAO station identifier (John F. Kennedy International Airport)
- 161853Z — Day of month (16th) and time in Zulu/UTC (18:53Z)
- 31015G25KT — Wind from 310 degrees true at 15 knots, gusting to 25 knots
- 10SM — Visibility 10 statute miles (the maximum reported value)
- FEW040 SCT080 BKN250 — Cloud layers: few at 4,000 ft AGL, scattered at 8,000 ft, broken at 25,000 ft
- 22/12— Temperature 22°C, dewpoint 12°C
- A3002 — Altimeter setting 30.02 inches of mercury
- RMK — Remarks section follows
- AO2 — Automated station with precipitation discriminator
- SLP168 — Sea-level pressure 1016.8 hPa
- T02220122— Precise temp/dewpoint: 22.2°C / 12.2°C
Weather phenomena and descriptors
Weather phenomena in METARs use standard two-character codes, optionally preceded by intensity qualifiers and descriptors. Understanding these codes is essential for quickly assessing conditions.
Intensity:Light (-), Moderate (no qualifier), Heavy (+). A METAR showing "-RA" means light rain, "RA" means moderate rain, and "+RA" means heavy rain.
Common precipitation codes: RA (rain), SN (snow), DZ (drizzle), PL (ice pellets), GR (hail), GS (small hail/snow pellets), IC (ice crystals), SG (snow grains), UP (unknown precipitation — automated stations only).
Obscuration codes: FG (fog, visibility below 5/8 SM), BR (mist, visibility 5/8 SM to 6 SM), HZ (haze), FU (smoke), DU (dust), SA (sand), VA (volcanic ash).
Descriptors: MI (shallow), BC (patches), PR (partial), DR (drifting), BL (blowing), SH (showers), TS (thunderstorm), FZ (freezing). These combine with phenomena: TSRA = thunderstorm with rain, FZRA = freezing rain, BLSN = blowing snow, +TSRA = heavy thunderstorm with rain.
Vicinity (VC): When weather is observed within 5-10 SM of the airport but not at the airport. VCTS = thunderstorm in the vicinity.
Understanding TAFs
A Terminal Aerodrome Forecast (TAF) predicts surface weather conditions at an airport for a specified period, typically 24 or 30 hours. TAFs are issued four times daily (at 0000Z, 0600Z, 1200Z, and 1800Z for 24-hour TAFs) and are amended when conditions deviate significantly from the forecast.
The TAF format is similar to METAR but includes forecast validity periods and change groups. Example:
TAF KORD 161730Z 1618/1724 28012KT P6SM SCT040 BKN080 FM162200 31018G28KT P6SM FEW050 TEMPO 1702/1706 4SM -SHRA BKN030 BECMG 1710/1712 22008KT SCT050
- 1618/1724 — Valid from 16th at 18Z to 17th at 00Z (24 hours)
- 28012KT P6SM SCT040 BKN080 — Initial conditions: wind 280 at 12, visibility greater than 6 SM, scattered 4,000, broken 8,000
- FM162200 — FROM: conditions change to the following at 22Z on the 16th (complete replacement of previous conditions)
- TEMPO 1702/1706 — TEMPORARY: between 02Z and 06Z on the 17th, conditions temporarily become 4SM light rain showers with broken clouds at 3,000
- BECMG 1710/1712 — BECOMING: between 10Z and 12Z on the 17th, conditions gradually transition to wind 220 at 8 with scattered 5,000
TAF change groups: FM, BECMG, TEMPO, PROB
Understanding TAF change groups is critical for flight planning. Each indicates a different type of expected change:
FM (From): A complete and permanent change in conditions at a specific time. All previously forecast conditions are replaced. FM groups always start on a new line and include a complete set of weather elements. Use FM to identify distinct weather periods in your planning.
BECMG (Becoming):A gradual change expected to occur over a specified time window (usually 2 hours). Only the changing elements are listed — unchanged elements carry forward from the previous group. For example, "BECMG 1710/1712 22008KT" means only the wind is expected to change; visibility and clouds remain as previously forecast.
TEMPO (Temporary): Temporary fluctuations expected during a specified time window. Each fluctuation lasts less than one hour, and the total time of fluctuations covers less than half the TEMPO period. TEMPO conditions alternate with the prevailing forecast. This is common for shower activity.
PROB (Probability): Indicates the probability (typically PROB30 or PROB40) of conditions occurring during a specified time window. PROB30 means a 30% chance. The FAA does not use PROB50 or higher — those conditions would be included in the main forecast. PROB groups are not issued for the first 6 hours of a TAF.
Flight category color coding
Aviation weather products use four standard flight categories based on ceiling and visibility. These are the color codes you see on weather maps, airport markers, and briefing products. The category is determined by the lowest qualifying value — either ceiling or visibility.
- VFR (Green): Ceiling greater than 3,000 feet AGL AND visibility greater than 5 statute miles. Standard visual flight conditions.
- MVFR (Blue): Ceiling 1,000 to 3,000 feet AGL AND/OR visibility 3 to 5 statute miles. Marginal conditions — legal VFR but requires caution, especially for less experienced pilots.
- IFR (Red): Ceiling 500 to below 1,000 feet AGL AND/OR visibility 1 to below 3 statute miles. Instrument flight rules required — VFR flight is not recommended and may be illegal depending on airspace.
- LIFR (Magenta): Ceiling below 500 feet AGL AND/OR visibility below 1 statute mile. Low instrument flight rules — the most restrictive conditions. Many instrument approaches have higher minimums than LIFR conditions.
Remember: the ceiling is the lowest cloud layer reported as broken (BKN) or overcast (OVC). Few (FEW) and scattered (SCT) layers are not considered ceilings. A METAR reporting "SCT015 BKN030" has a ceiling of 3,000 feet, not 1,500 feet.