• METAR: current
  • TAF: forcast

Online services


METAR is a format for reporting weather information.

  • Wind: direction from which the wind is blowing + speed.
    • E.g. 12015G20KT: wind from 120 degree, 15 knots, G gusting 20 knots
  • Visibility: in statue miles e.g. 5SM
  • Weather: -RA=light rain +RA=heavy rain, BR=mist(from French word "brume")
  • Cloud: SCT048 = scattered cloud layer at 4800' AGL, BKN065: broken
  • 150V210=variable wind between 150 degree and 210 degree
  • VRB005KT=Wind direction is vairable, speed is less than 6 kts
  • OVC008CB, CB=Cumulonimbus
  • VV008: sky obscured with a vertical visibility of 800'.


  • AO1: weather sensor that cannot discriminate between freezing and non-freezing precipitation.
  • A02: the site is automated and HAS a precipitation sensor; can discriminate between freezing and non-freezing precipitation.
  • TSE36: Thunderstorm ended 36 minutes past the hour
  • PRESFR: Pressure is falling rapidly
  • SLP – Sea Level Pressure
  • RAESNB42M: Rain ended and snow began 42 minutes past the hour.

If there is an AUTO after the ID in the metar ob, then there is no observer (un-manned).

Special code:

  • 9900: the forecast speed is less than 5 knots, read "LIGHT AND VARIABLE".
  • 9999: used in some international METARs and TAFs to indicate that visibilities are 10 KM or above. This is not used in US METARs or - TAFs.
  • 0000: used in some international METARs and TAFs to indicate that visibilities are less than 50 meters. This is not used in US METARs or TAFs.


  • UA: Routine report.
  • UUA: urgent upper air report.
  • OV: location ("over"?)
  • TM: time.
  • FL: flight level, altitude
  • TP: aircraft type.
  • SK: sky cover.
  • WX: weather.
  • TA: temperature (Celsius)
  • WV: wind
  • TB: turbulence.
  • IC: icing.
  • RM: Remarks.
  • RM +/- 15 KTS ON FINAL indicates a remark reporting a plus or minus 15 knot variation of airspeed on final approach.


  • BL: between layers

Winds and Temperature Aloft Forecast (FD)

If a wind direction is coded between 51 and 86, the wind speed is 100 knots or greater. To decode, subtract 50 from the direction and add 100 knots to the speed. "830558" is 83 - 50 = 33(0), 05 + 100 = 105 knots, and a -58° C temperature.


ATIS: Automatic terminal information service, broadcasts essential information like weather, active runways, available approaches, etc.

  • (Voice) ATIS: tune in the frequency to listen.
  • D-ATIS: Data-link ATIS, is text-based, can be displayed on an electronic display in the aircraft.


  • ATIS: Automatic Terminal Information Service. contains current, routine information to arriving and departing aircraft as well as weather reports derived from human data collection that is updated hourly or upon pertinent data changes.
  • AWOS: Automated Weather Observing System. Typically includes ceiling and sky conditions, visibility, temperature, dew point, altimeter setting and wind speed, gusts and direction.
  • ASOS: Automated Surface Observing System. Can additionally provide the type and intensity of precipitation (rain, snow, freezing rain), and obstructions to visibility such as fog and haze.


  • ATIS is by human recording. AWOS and ASOS are automated.
  • ATIS is generated hourly (or as required); AWOS is minute-by-minute.
  • ASOS is similar to AWOS but is managed, maintained and controlled by NOAA rather than the FAA or the organization that operates the airport.


SIGMET (Significant Meteorological Information)

AIRMETs cover less severe weather: moderate turbulence and icing, sustained surface winds of 30 knots or more, or widespread restricted visibility. SIGMETs cover more severe weather.

3 types of AIRMET

  • S (Sierra)
  • T (Tango)
  • Z (Zulu)

3 main types of SIGMET:

  • Volcanic ash (VA or WV SIGMET)
  • Tropical Cyclone (TC SIGMET)
  • Other En-route weather phenomenon (WS SIGMET)

AIRMETs are valid for six hours. SIGMET valid up to four hours. SIGMETS for hurricanes and volcanic ash outside the CONUS are valid up to six hours.

Both broadcast on the ATIS at ATC facilities, as well as over VOLMET stations


  • PIREP in MSL
  • METAR in AGL

Ice pellets and hail

Thunderstorms may create hail rather than ice pellets.

Rain falling through colder air may freeze during its descent falling as ice pellets. Ice pellets always indicate freezing rain at higher altitudes.

Update frequency

  • METAR: update every hour
  • TAF: update every 6 hour, each has a 24 hour forecast period


  • Radiation fog does not form over water. Under stable nighttime conditions, long-wave radiation is emitted by the ground; this cools the ground, which causes a temperature inversion.
  • Advection fog forms when moist air moves over colder ground or water. It deepens as the wind speed increases up to 15 knots.
  • Upslope fog: occurs when sloping terrain lifts air, cooling it adiabatically to its dew point and saturation. Upslope winds more than 10 to 12 knots usually result in stratus rather than fog.
  • Steam fog (arctic sea smoke): In northern latitudes, steam fog forms when water vapor is added to air that is much colder, then condenses into fog.
  • Frontal fog. Associated with frontal zones and frontal passages.
    • warm-front pre-frontal fog;
    • cold front post-frontal fog;
    • frontal-passage fog.
  • Ice fog. Ice fog is composed of ice crystals instead of water droplets and forms in extremely cold, arctic air



  • single-cell
  • multi-cell
  • squall line
  • supercell (capable of producing tornados)

Formation of thunderstorms: Sufficient moisture, an unstable lapse rate, and a lifting action.


幡状云(学名:Virga,缩写: vir )是一种从云中落下的降水,但还没到地面前就已经蒸发。


  • advection 平流
  • convection 对流



  • +: Heavy
  • -: Light
  • VC: Vicinity
  • MI Shallow (MI = MInce, French origin)
  • PR Partial
  • BC Patches (BC = BanCs, French origin)
  • DR Low Drifting
  • BL Blowing
  • SH Shower(s)
  • TS Thunderstorms
  • TSRA: Thunderstorm with Rain
  • FZ Freezing
  • WDSPR: Widespread.


  • DZ Drizzle
  • RA Rain
  • SN Snow
  • SG Snow Grains
  • IC Ice Crystals (Diamond Dust)
  • PL Ice Pellets
  • GR Hail
  • GS Snow Pellets
  • UP Unknown Precipitation


  • BR Mist
  • FG Fog
  • FU Smoke
  • VA Volcanic Ash
  • DU Widespread Dust
  • SA Sand
  • HZ Haze
  • PY Spray
  • DRDU: Drifting Dust
  • DRSA: Drifting Sand

Other Weather

  • PO Dust/Sand Whirls
  • SQ Squalls
  • FC Funnel Cloud, Tornado or Waterspout
  • SS Sandstorm
  • DS Dust Storm


  • CIG: Ceiling.