1. How many sites are operated under the ASOS program?
Currently, there are 953 active ASOS sites.
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2. What are the differences between ASOS and AWOS?
Both systems work to support the reporting of accurate meteorological data to the NWS and FAA for the purposes of weather forecasting and real-time data for aviation safety and are part of the . Whereas AWOS data typically includes ceiling and sky conditions, visibility, temperature, dew point, altimeter setting, and wind speed, gusts, and direction, ASOS can additionally provide type and intensity of precipitation and obstructors to visibility such as fog and haze.
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3. When was the ASOS program established?
The initial deployment of hardware at ASOS sites began in 1991 and was completed in 2004.
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4. What are the primary components at a standard ASOS site?
A standard ASOS site will consist of a sensor array of meteorological sensors that includes a 10 meter wind tower, one or more data collection package units (DCP) that take sensor data and package it for transmission to an acquisition control unit (ACU) where algorithms are applied and the observations are transmitted to end users. The physical sensor group typically requires an area of 75ft. by 59ft. clear of debris, ground obstructions, reflective surfaces, and light sources.
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5. Who receives the information that is observed and transmitted from each ASOS site?
There are two types of data transmissions from ASOS, Local and Long Line. Observations are initially viewed by local airport personnel on dedicated terminals and they are also sent to other systems operating at the location being serviced by the ASOS. The long line transmission goes to the National Centers for Environmental Prediction where the observations are then distributed to global networks over the Internet.
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6. How many ASOS sites are located at non-airport locations?
There are 35 ASOS sites not co-located with an aerodrome
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7. Where can I see a schedule for planned maintenance/upgrades at a particular ASOS site?
Maintenance schedules for ASOS sites are published in Engineering handbook #4 and is not available to the general public. The schedule however is based on the equipment maintenance intervals recommended by the manufacturer the most common being a quarterly preventative maintenance followed by semiannual, annual and biennial preventative maintenance regimes.
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8. How does ASOS operation affect commercial aviation?
ASOS is a critical component for aviation safety as it provides real-time local weather information directly to pilots and air traffic control. Real-time weather and altimeter information are essential for safe operation of commercial aircraft and, if the local ASOS at an airport is not functioning properly, a qualified weather observer must be present on site to provide the necessary information for any incoming flight.
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9. Who maintains the historical data that has been recorded by the ASOS sites and what is that data used for?
The National Centers for Environmental Information (NCEI) is the official climatological archive of all weather observations.
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10. What weather parameters are observed by a standard ASOS site?
ASOS sites track wind speed, direction, and gusts, temperature, dew point, altimeter setting, cloud height and type, visibility, present weather, precipitation identification and accumulation, and thunderstorm occurrence.
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11. Who is responsible for ASOS corrective repairs and maintenance?
The ASOS Operations and Monitoring Center (AOMC) provides around-the-clock operational monitoring support for the ASOS network and is the single point of contact for any operational issue i.e. missing observations, missing observational elements etc.. The AOMC is the tier-one service desk providing real-time monitoring, triage of identified issues and remote diagnostic for identifying, tracking and documenting ASOS malfunctions. The AOMC can be reached via email at aomc@noaa.gov or 1 (800) 242-8194.
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12. Where can I get a list of all ASOS sites?
Here is a link to all active ASOS sites that the NWS maintains.
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13. What are the planned upgrades for the ASOS sensors?
The NWS has undertaken a comprehensive plan to replace most of the sensors on the ASOS sensor array by the end of 2030. The plan is already in action and the status is: Wind sensor: Vaisala Inc. is the manufacturer of the new ASOS wind sensor. It is the WMT-702 model with heated transducer tips. It is known as an Ice Free Wind Sensor (IFWS). The original contract was awarded in 2017 and is now fully executed. NWS technicians will be completing the deployment of all the new wind sensors by 30 September 2023. Temperature/Dew Point (RH) Sensor (TRH):Vaisala Inc. is the manufacturer of the new ASOS Temperature and Relative Humidity sensor. It is the HUMICAP® Humidity and Temperature Probe HMP155. The original contract was awarded in September 2021 and is still active. The NWS has completed integration testing into the ASOS and is now preparing for operational test and evaluation and full scale National Operational Implementation. Barometer Sensor: Planned for FY2024. Precipitation Accumulation Sensor: Planned for FY2024 Ceilometer: Planned for FY2024 Visibility and Present Weather: Planned for FY2025 Other sensors are in the planning development stage; this FAQ will be updated annually as the projects progress. Last update was April 28, 2023. Back to top
14. Can I connect directly to an ASOS to get its data or weather observations?
Currently this is not possible, however there are plans to make high-frequency ASOS data available through a proxy. When it is ready to debut into the production environment, it will be announced. The most recent METAR is available on the Aviation Weather site METAR page.
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15. Is it intened to continue forward with two distinct types of Surface Observing Systems?
Currently there are several different types of surface observing systems. More information about the number of systems and their placement in the Automated Surface Weather Observing Network (ASWON) can be found Here Back to top
16. Does NWS intend to transition their ASOS systems to AWOS as well, and if so, when?
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NWS and FAA Transitioning 207 Sites:
17. Why is the NWS and FAA transitioning 207 ASOS sites to AWOS-C?
The FAA funding budgeted for this upgrade is insufficient to recondition all 570 FAA ASOS locations to the modernized processing and dissemination integrated systems. The decision to transition to the AWOS-C in lieu of ASOS 2.0 was therefore a budgetary decision by the FAA. Back to top
18. What sites will be affected under the 207 transition and what parameters were used for their selection?
See a complete list here Back to top
19. When will the ASOS to AWOS-C Transition happen?
The schedule currently has a start date of 2025 and lasts through 2029. Back to top
20. Who can I contact about the ASOS to AWOS-C?
Mr. Steve Kim and Mr. Jerry Krantz. steve.kim@faa.gov, jerry.ctr.kranz@faa.gov. Back to top
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