Altimeter Setting
The current local atmospheric pressure value set in an aircraft’s altimeter to ensure correct indication of altitude above mean sea level, typically given in hectopascals (hPa) or inches of mercury (inHg).
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Meteorology
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Altimeter Setting to Aerodrome Elevation
The altimeter setting that displays the elevation of the aerodrome as the altitude on the altimeter when on the ground. Referred to as QFE in ICAO terminology.
View termAltimeter Setting to Mean Sea Level Pressure
The altimeter setting that corresponds to the atmospheric pressure at mean sea level. Referred to as QNH in ICAO phraseology.
View termAltimeter Setting Using Standard Pressure
An altimeter setting based on the standard pressure of 1013.25 hPa or 29.92 inHg, used above the transition altitude. Known as QNE in ICAO terminology.
View termaltocumulus castellanus cloud
Medium-level turreted cloud with rising towers indicating mid‑level instability, possible precursor to thunderstorms.
View termanti‑icing
Application of fluid to prevent ice formation during ground operations or flight.
View termArea Forecast for Low-Level Flights
A GAMET area forecast describing significant weather below FL100 (or FL150 over mountainous terrain) within a FIR, supporting VFR and low-level IFR planning.
View termAtmospheric Sounding
A vertical profile of the atmosphere obtained by balloon or remote sensing, recording temperature, humidity, wind, and pressure at various altitudes for weather analysis and flight planning.
View termAutomated Weather Observing System
An unattended station that continuously measures and broadcasts real-time surface weather elements to pilots and ATC on a discrete frequency.
View termAutomatic Terminal Information Service
A continuous broadcast of recorded aerodrome information, including weather, runways and NOTAMs, provided to reduce controller-pilot communication workload.
View termBarometric Pressure
The atmospheric pressure as measured by a barometer, used to determine altimeter settings and to ensure altitude accuracy during flight operations.
View termbraking action
Pilot- or airport-reported assessment of runway surface stopping quality: good/medium/poor/nil.
View termceiling
Height above ground at which an unbroken or overcast cloud layer exists.
View termClear Icing
The formation of smooth, transparent ice on aircraft surfaces, resulting from slow freezing of large supercooled water droplets.
View termclear-air turbulence
Turbulence occurring in clear skies, typically at high altitudes near the jet stream, with no visible weather phenomena.
View termcloud base
Lowest altitude of the visible cloud layer, reported as base of scattered, broken, overcast.
View termCold Front
A weather front where a cold air mass advances and displaces a warmer air mass, often producing showers, thunderstorms, and abrupt changes in wind and temperature.
View termcontaminated runway
Runway with >25% surface covered by standing water ≥3 mm, slush, snow, ice.
View termcumulonimbus cloud
Towering vertical cloud with significant turbulence, precipitation, and lightning potential.
View termde‑icing
Removal of existing frost, ice or snow from aircraft surfaces before flight.
View termembedded cumulonimbus cloud
Cumulonimbus cloud obscured within other cloud layers, not visually identifiable, but with severe turbulence and precipitation.
View termFreezing Level
The lowest altitude in the atmosphere at which the air temperature drops to 0°C (32°F), marking the boundary where liquid water can freeze.
View termgust
A sudden, brief increase in wind speed, typically varying with rapid fluctuations.
View termHigh Pressure
An area of the atmosphere where the pressure is higher than that of the surrounding region, often associated with stable weather, clear skies, and reduced turbulence.
View termhold‑over time
Estimated time fluid will prevent ice before need for re‑application.
View termIcing
The accumulation of ice on aircraft surfaces due to supercooled water droplets, which can affect aerodynamics and instrument performance.
View termInternational Standard Atmosphere
A model of the atmosphere based on standard average conditions at sea level, used for calibrating instruments and performance calculations. Defined by ICAO: 15°C, 1013.25 hPa, and lapse rate of 2°C per 1000 ft.
View termInternational Standard Atmosphere Deviation
The difference between the actual atmospheric temperature and the standard temperature defined by the International Standard Atmosphere at a given altitude.
View termjet stream
A narrow, fast-flowing air current in the upper atmosphere, typically between 20 000 and 50 000 ft, affecting cruise performance.
View termLow Pressure
An area of the atmosphere where the pressure is lower than that of the surrounding region, often associated with unsettled weather, precipitation, and potential turbulence.
View termlow‑level wind shear
Wind shear occurring below 2 000 ft AGL, especially hazardous during takeoff and landing phases.
View termMeteorological Aerodrome Report
Routine coded weather observation for a specific aerodrome at a specific time.
View termmicroburst
A small, intense downdraft producing damaging winds near the ground, hazardous to aircraft during takeoff or landing.
View termmixed icing
Presence of both rime and clear ice types on aircraft surfaces.
View termmoderate turbulence
Turbulence that causes changes in altitude and/or attitude but aircraft remains in control; occupants may feel strain against seat belts.
View termMountain Wave
A standing atmospheric wave created when stable air flows over a mountain or ridge, often causing turbulence and rotor clouds.
View termOccluded Front
A composite weather front formed during the process of cyclogenesis when a cold front overtakes a warm front, leading to complex weather patterns including precipitation and changes in wind direction.
View termPressure Altitude
The altitude indicated by a barometric altimeter set to the standard pressure setting of 1013.25 hPa or 29.92 inHg. Used as a reference for aircraft performance calculations.
View termprevailing visibility
Greatest visibility value equaled or exceeded for at least half the horizon.
View termPrognostic Chart
A weather chart produced by meteorological authorities that forecasts the expected positions of pressure systems, fronts, and significant weather for a specified future time.
View termRime Icing
The formation of rough, milky, opaque ice due to rapid freezing of supercooled water droplets on aircraft surfaces.
View termRotor Cloud
A turbulent, low-level cloud formation found downwind of mountain ranges, forming in the rotor zone beneath and near mountain waves; indicative of severe turbulence and hazardous for aviation.
View termrunway condition report
Aerodrome-issued report of runway surface condition using RCAM and RWYCC.
View termrunway friction
Measurement of friction coefficient between tires and runway; indicates braking performance.
View termrunway visual range
Distance over which runway markings or lights are visible from centreline on approach.
View termsevere turbulence
Turbulence that causes large, abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control. Occupants are forced violently against seat belts.
View termShort-Term Trend Forecast
A TREND appended to a METAR or SPECI giving expected significant changes in surface wind, visibility, weather or cloud over the next two hours.
View termSignificant Meteorological Information
A weather advisory issued by a Meteorological Watch Office concerning significant en‑route weather hazards affecting flight safety.
View termSignificant Temperature Level
A specific altitude or flight level at which temperature changes are forecast to be significant for flight operations, affecting aircraft performance, icing risk, or fuel management.
View termSignificant Weather Chart
A meteorological chart that displays forecasted significant weather phenomena, including turbulence, icing, and cumulonimbus clouds, relevant for flight safety at specific flight levels.
View termSkew-T Log-P Diagram
A thermodynamic diagram used in meteorology to plot atmospheric soundings, displaying temperature, dew point, and wind profiles with altitude to assess atmospheric stability and forecast weather hazards.
View termSnow Notice to Airmen
Special NOTAM issued when snow, ice or slush significantly affects aerodrome movement areas.
View termSpecial Aerodrome Report
An unscheduled aerodrome weather report issued when significant meteorological changes occur between routine METARs.
View termsquall
Sudden increase in wind speed of at least 15 knots, sustained for at least one minute.
View termStanding Lenticular Cloud
A smooth, lens-shaped cloud that forms at high altitudes in the crest of mountain waves; often stationary, and indicative of significant atmospheric turbulence downwind of mountain ranges.
View termsupercooled large droplet
Liquid droplets below freezing point that can remain liquid until striking an object.
View termSurface Analysis Chart
A weather chart depicting current meteorological features such as pressure systems, fronts, and precipitation areas at the Earth's surface; essential for flight planning and enroute weather briefing.
View termTemperature Inversion
A meteorological condition where temperature increases with altitude instead of decreasing, which can trap pollutants and affect aircraft climb performance.
View termTerminal Aerodrome Forecast
A concise statement of the expected meteorological conditions at an aerodrome for a specified period.
View termthunderstorm
Convective weather event with thunder, lightning, precipitation and possible severe turbulence.
View termtowering cumulus cloud
Large cumulus cloud with strong vertical development, indicating convective activity, but not yet cumulonimbus.
View termTropical Cyclone Significant Meteorological Information
A SIGMET issued for a tropical cyclone within or approaching an FIR, including observed or forecast TC position, extent of associated cumulonimbus clouds, movement and intensity.
View termtropopause
The boundary layer between troposphere and stratosphere, marked by a temperature inversion, affecting flight levels and turbulence potential.
View termturbulence
Irregular atmospheric motion caused by eddies and vertical currents, affecting aircraft stability, comfort, and sometimes control.
View termUpper-Air Chart
A meteorological chart depicting wind, temperature, and pressure patterns at specified altitudes above the earth’s surface, used to forecast enroute weather conditions for aviation operations.
View termvisibility
Greatest distance at which prominent objects are visible and identifiable by day.
View termVolcanic Ash Significant Meteorological Information
A SIGMET concerning volcanic ash clouds that may affect en‑route flight safety.
View termWarm Front
A boundary where a warm air mass advances and rises over a retreating cold air mass, usually resulting in steady precipitation and lower clouds along the front.
View termWind and Temperature Aloft Message
A meteorological report providing forecasted wind direction, wind speed, and temperature at specific altitudes above mean sea level, used for flight planning and fuel calculations.
View termWind Barb
A graphic symbol used on meteorological charts to represent wind speed and direction at a specific location and altitude, typically shown as a shaft with barbs and pennants.
View termwind shear
A sudden change in wind speed and/or direction over a short distance, hazardous during takeoff and landing.
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