The Automated Surface Observing Systems (ASOS) program is a joint effort of the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the Department of Defense (DOD). The ASOS
... systems serves as the nation's primary surface weather observing network. ASOS is designed to support weather forecast activities and aviation operations and, at the same time, support the needs of the meteorological, hydrological, and climatological research communities.
With the largest and most modern complement of weather sensors, ASOS has significantly expanded the information available to forecasters and the aviation community. The ASOS network has more than doubled the number of full-time surface weather observing locations. ASOS works non-stop, updating observations every minute, 24 hours a day, every day of the year.
Elements Reported:
1. Sky condition:cloud height and amount (clear, scattered,
broken, overcast) up to 12,000 feet
2. Visibility (to at least 10 statute miles)
3. Basic present weather information: type and intensity for
rain, snow, and freezing rain
4. Obstructions to vision: fog, haze
5. Pressure: sea-level pressure, altimeter setting
6. Ambient temperature, dew point temperature
7. Wind: direction, speed and character (gusts, squalls)
8. Precipitation accumulation
9. Selected significant remarks including- variable cloud
height, variable visibility, precipitation beginning/ending
times, rapid pressure changes, pressure change tendency, wind
shift, peak wind
[Source: National Weather Service] 
