Automated Surface Observing System
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The Automated Surface Observing System (ASOS), Automated Weather Observing System (AWOS), and Automated Weather Sensor System (AWSS) are sensor packages used to measure and record hourly and significant weather conditions at airports across the United States. ASOS units are implemented cooperatively, with the National Weather Service operating them and the Federal Aviation Administration (FAA) distributing information to pilots. AWOS and AWSS units are operated and controlled by the FAA, as well as by state and local government and private agencies; the NWS plays no role in their operation or deployment. Data dissemination is usually via an automated VHF airband radio frequency (118~136MHz) at each airport, broadcasting ASOS, AWOS or AWSS weather information, often via the Automatic Terminal Information Service (ATIS).
ASOS, AWOS, and AWSS units record temperature, visibility (haze or fog), precipitation types and amounts, wind direction and speed, humidity and dew point, barometric pressure and altimeter, sky cover and ceiling, and thunder. Freezing rain is recorded with a vibrating wire, which stops vibrating as ice accumulates. Regular reports are made at different intervals depending on the unit type. ASOS and AWSS units report hourly, usually a few minutes before the hour, with additional SPECI (special) reports when significant changes in weather occur during the hour, such as rain changing to snow, approaching thunder, or heavy rain. AWOS units report every 20 minutes, though this occasionally varies by a few minutes; they do not issue SPECIs.
The data helps meteorologists, pilots and flight dispatchers prepare and monitor weather forecasts, flight routes, and provide necessary information for safe takeoffs and landings. AWOSs are categorized as either "federal" or "non-federal". Federal AWOSs were purchased and are maintained by the FAA. Non-federal AWOSs are purchased and maintainted by state government, local government, and private organizations. The current information reported by ASOS, AWOS and AWSS units is used at weather offices where forecasts are produced, along with computer model outputs, weather satellite photos, and weather radar images, to name a few.
Not all U.S. government weather stations are NWS- or FAA-run. The Remote Automated Weather Station (RAWS) system is run by the U.S. Forest Service and Bureau of Land Management and monitored by the National Interagency Fire Center, mainly to observe potential wildfire conditions.
| Meteorological Observation Systems and Weather Stations (Earth based) |
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Argo | Global Atmosphere Watch | Automatic weather station | Remote Automated Weather Stations (RAWS) | Automated Surface Observing System (ASOS) | Meteorological Aerodrome Report (METAR) | NEXRAD radar | Global Sea Level Observing System | SST buoys | Hurricane Hunters | Dropsonde | Weather balloon |
