Glossary
Aviation weather glossary
If you're a pilot, weather is a foreign language. Here are the terms that appear on every METAR, TAF, and briefing — decoded.
Common reports and forecasts
- METAR — surface weather observation. Updated hourly.
- SPECI — special METAR when conditions change fast.
- TAF — Terminal Aerodrome Forecast. 24-30 hr forecast for airport.
- AIRMET — weather warning for light aircraft.
- SIGMET — significant weather warning for all aircraft.
- PIREP — pilot report. In-flight weather observation.
- Center Weather Advisory (CWA) — short-term advisory issued by air traffic control centers.
Cloud terms
- FEW — 1-2 oktas cloud coverage.
- SCT — scattered, 3-4 oktas.
- BKN — broken, 5-7 oktas.
- OVC — overcast, 8 oktas.
- CB — cumulonimbus. THE cloud type to avoid.
- TCU — towering cumulus. May grow into CB.
- VC — in vicinity (within 10 SM but not at airport).
Precipitation and obscurations
- RA — rain, SN — snow, PL — ice pellets, GR — hail.
- SHRA — rain showers. TSRA — thunderstorm with rain.
- FZRA — freezing rain. Highest-priority aviation hazard.
- FG — fog. BR — mist (better than 5/8 SM but reduced vis).
- HZ — haze. FU — smoke. DU — dust.
- + intense, - light, no sign = moderate.
Danger terms
Microburst
Rapidly descending column of air. Killed Delta 191 in 1985. Modern predictive windshear alerts (PWS) warn on approach.
Wind shear
Rapid change in wind direction or speed with distance. Killed L-1011 crew on approach to DFW. Now detected by TDWR at every major US airport.
Mountain wave
Turbulent flow downwind of mountain range. Can extend 100+ miles. Rotor clouds mark the danger zone.
Virga
Precipitation that evaporates before reaching ground. Dry air below can cool rapidly = microburst risk.
Icing (SLD)
Supercooled Large Droplets. Freezes on impact. Boots don't remove SLD ice.
Freezing level
Altitude where temperature = 0°C. Above = potential icing in visible moisture.
Density altitude
Pressure altitude corrected for temperature. High DA = poor engine and lift performance.
CAT
Clear Air Turbulence. Usually near jet stream. No visual clues.
Wind terms
- VRB — variable wind direction.
- G — gust. Written like "10G20" (10 kt gusting 20).
- WS — wind shear (low-level).
- LLWS — Low-Level Wind Shear.
- KT — knots. Always knots in METAR.
- 250° — from-direction always in degrees magnetic in TAF/METAR; true north in weather charts.
Pressure and altimeter
- A2992 — altimeter setting 29.92 inches Hg.
- Q1013 — QNH 1013 hPa (used outside US).
- FL180 — Flight Level 180 = 18,000 ft when altimeter = 29.92.
- Standard Pressure — 29.92 in Hg / 1013.25 hPa.
- Density Altitude — the altitude the airplane "feels" it's at.
The METAR format
A METAR looks like: METAR KOKC 011255Z AUTO 24012KT 3/4SM +TSRA BR OVC008CB 25/24 A2985 RMK...
KOKC— ICAO airport code (Oklahoma City).011255Z— Day 01 at 1255 UTC.AUTO— automated observation.24012KT— wind from 240° at 12 knots.3/4SM— visibility 3/4 statute mile.+TSRA BR— heavy thunderstorm with rain and mist.OVC008CB— overcast at 800 ft with cumulonimbus.25/24— temp 25°C / dewpoint 24°C.A2985— altimeter 29.85.RMK— remarks (encoded).