Aviation Weather Glossary
Comprehensive reference for aviation weather terms and codes
Last updated: February 4, 2026
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102+ terms
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Weather Reports & Forecasts
METAR
Meteorological Aerodrome Report - A standardized format for reporting weather observations at airports, typically issued hourly.
SPECI
Special METAR - An unscheduled weather observation issued when significant weather changes occur between regular METAR times.
TAF
Terminal Aerodrome Forecast - A weather forecast for the area within 5 statute miles of an airport runway complex, valid for 24-30 hours.
SIGMET
Significant Meteorological Information - Advisory for weather phenomena potentially hazardous to all aircraft: severe turbulence, icing, volcanic ash.
AIRMET
Airman's Meteorological Information - Advisory for weather phenomena potentially hazardous to light aircraft: moderate turbulence/icing, IFR conditions, mountain obscuration.
PIREP
Pilot Report - Weather observations made by pilots in flight, providing real-time conditions that may not appear in surface observations.
FA
Area Forecast - A forecast of general weather conditions over a large region.
TWEB
Transcribed Weather Broadcast - Recorded weather information available by phone or radio.
Cloud Types & Coverage
SKC
Sky Clear - No clouds present (manual observation).
CLR
Clear - No clouds below 12,000 feet (automated observation).
FEW
Few clouds - 1/8 to 2/8 sky coverage (1-2 oktas).
SCT
Scattered - 3/8 to 4/8 sky coverage (3-4 oktas). Not a ceiling.
BKN
Broken - 5/8 to 7/8 sky coverage (5-7 oktas). Constitutes a ceiling.
OVC
Overcast - 8/8 sky coverage (8 oktas). Full cloud cover.
VV
Vertical Visibility - Height into an obscured sky (fog, heavy precipitation).
CB
Cumulonimbus - Thunderstorm cloud. Indicates convective activity, severe turbulence, lightning, hail possible.
TCU
Towering Cumulus - Tall cumulus cloud indicating developing convection. May become CB.
CEILING
The height of the lowest layer of clouds reported as broken (BKN) or overcast (OVC), or vertical visibility into an obscured sky.
Visibility & Obscurations
SM
Statute Miles - Unit of visibility measurement in US METARs.
KM
Kilometers - Unit of visibility measurement in international METARs.
9999
Visibility 10 km or more (international METARs) - Essentially unlimited visibility.
FG
Fog - Visibility less than 5/8 statute mile due to water droplets.
BR
Mist - Visibility 5/8 mile to 6 miles due to water droplets.
HZ
Haze - Visibility reduction due to fine particles (dust, smoke, pollution).
FU
Smoke - Visibility reduction due to combustion products.
DU
Dust - Widespread dust reducing visibility.
SA
Sand - Sand particles in the air reducing visibility.
VA
Volcanic Ash - Particulates from volcanic eruption. Extremely hazardous to aircraft.
PY
Spray - Water spray reducing visibility (usually near waterfalls or large bodies of water).
Precipitation Types
RA
Rain - Liquid precipitation.
DZ
Drizzle - Fine liquid precipitation (drops less than 0.5mm).
SN
Snow - Frozen precipitation in crystalline form.
SG
Snow Grains - Very small, flat, opaque ice particles.
IC
Ice Crystals - Tiny ice crystals (diamond dust) visible in very cold conditions.
PL
Ice Pellets - Frozen rain that bounces on impact (sleet).
GR
Hail - Ice balls 5mm or greater in diameter.
GS
Small Hail/Snow Pellets - Ice particles less than 5mm.
UP
Unknown Precipitation - Automated stations cannot determine precipitation type.
FZRA
Freezing Rain - Rain that freezes on contact with cold surfaces. Severe icing hazard.
FZDZ
Freezing Drizzle - Drizzle that freezes on contact. Icing hazard.
Weather Phenomena
TS
Thunderstorm - Convective activity with lightning. Often accompanied by gusty winds, heavy precipitation, hail.
SH
Showers - Precipitation from convective clouds. Characterized by rapid changes in intensity.
FZ
Freezing - Prefix indicating supercooled water that freezes on contact.
MI
Shallow - Fog or other phenomena extending less than 6 feet above ground.
PR
Partial - Covering part of the airport but not all.
BC
Patches - Fog or other phenomena occurring in patches.
DR
Drifting - Snow or other particles being moved by wind but staying close to the ground.
BL
Blowing - Snow, dust, or sand being raised well above the ground by wind.
SQ
Squall - Sudden, sharp increase in wind speed lasting at least one minute.
FC
Funnel Cloud - Rotating column of air extending from cloud base but not touching ground.
+FC
Tornado or Waterspout - Funnel cloud that has reached the ground or water surface.
SS
Sandstorm - Intense dust/sand storm significantly reducing visibility.
DS
Duststorm - Storm with dust reducing visibility below 1000 meters.
PO
Dust/Sand Whirls - Well-developed rotating columns of dust or sand.
Wind Terms
KT
Knots - Unit of wind speed (1 knot = 1.15 mph = 1.85 km/h).
MPS
Meters Per Second - Alternative wind speed unit used internationally.
G
Gusts - Rapid fluctuations in wind speed. Reported when peak exceeds sustained by 10+ knots.
VRB
Variable - Wind direction varying too much to assign a single direction (usually with speeds < 6 knots).
00000KT
Calm - Wind speed less than 1 knot.
WSHFT
Wind Shift - Significant change in wind direction.
PK WND
Peak Wind - Maximum instantaneous wind speed recorded.
WS
Wind Shear - Sudden change in wind speed and/or direction. Hazardous on approach/departure.
Pressure & Altimetry
A
Altimeter Setting (US) - Atmospheric pressure in inches of mercury (e.g., A3012 = 30.12" Hg).
Q
Altimeter Setting (International) - Atmospheric pressure in hectopascals (e.g., Q1013 = 1013 hPa).
SLP
Sea Level Pressure - Atmospheric pressure reduced to sea level, in hectopascals (e.g., SLP203 = 1020.3 hPa).
PA
Pressure Altitude - Altitude indicated when altimeter is set to 29.92" Hg (standard pressure).
DA
Density Altitude - Pressure altitude corrected for non-standard temperature. Affects aircraft performance.
ISA
International Standard Atmosphere - Standard conditions: 15°C at sea level, 29.92" Hg, lapse rate 2°C/1000ft.
Temperature Terms
T
Temperature - Reported in degrees Celsius in METARs.
DP
Dewpoint - Temperature at which air becomes saturated and condensation occurs.
M
Minus/Below Zero - Prefix for temperatures below 0°C (e.g., M05 = -5°C).
SPREAD
Temperature-Dewpoint Spread - Difference between temperature and dewpoint. Small spread indicates high humidity.
TAF Change Groups
FM
From - Complete change in conditions expected at specified time.
TEMPO
Temporary - Temporary fluctuations expected to last less than one hour each time.
BECMG
Becoming - Gradual change in conditions expected over 2-hour period.
PROB
Probability - Likelihood of conditions occurring (usually 30% or 40%).
NSW
No Significant Weather - No weather phenomena expected.
NOSIG
No Significant Change - Trend indicator meaning conditions will persist.
CAVOK
Ceiling And Visibility OK - Visibility 10km+, no clouds below 5000ft, no significant weather.
Flight Categories
VFR
Visual Flight Rules - Ceiling > 3000 feet AND visibility > 5 statute miles. Best flying conditions.
MVFR
Marginal VFR - Ceiling 1000-3000 feet AND/OR visibility 3-5 statute miles. Requires extra caution.
IFR
Instrument Flight Rules - Ceiling 500-1000 feet AND/OR visibility 1-3 statute miles. Instrument rating required.
LIFR
Low IFR - Ceiling < 500 feet AND/OR visibility < 1 statute mile. Most restrictive conditions.
Remarks & Codes
RMK
Remarks - Additional information section of METAR.
AO1
Automated Observation Type 1 - Automated station without precipitation discriminator.
AO2
Automated Observation Type 2 - Automated station with precipitation discriminator.
PRESFR
Pressure Falling Rapidly - Pressure dropped 0.06" Hg or more in past 3 hours.
PRESRR
Pressure Rising Rapidly - Pressure rose 0.06" Hg or more in past 3 hours.
CIG
Ceiling - Used in remarks for variable or secondary ceiling reports.
TWR VIS
Tower Visibility - Visibility as observed from the control tower.
SFC VIS
Surface Visibility - Visibility at ground level.
VIRGA
Virga - Precipitation falling but evaporating before reaching the ground.
NOTAM Terms
NOTAM
Notice to Air Missions - Official notices about conditions affecting flight safety.
TFR
Temporary Flight Restriction - Airspace restriction for safety, security, or special events.
RWY
Runway - The paved surface used for takeoff and landing.
TWY
Taxiway - Paved surface for taxiing between runway and parking areas.
CLSD
Closed - Facility or surface is not available for use.
OTS
Out of Service - Equipment or facility temporarily unavailable.
U/S
Unserviceable - Same as OTS, equipment not working.
PERM
Permanent - NOTAM condition has no end date.
WEF
With Effect From - Indicates when a condition begins.
TIL
Until - Indicates when a condition ends.