Ask ACUKWIK: The Difference Between ASOS and AWOS

I often see ASOS and AWOS frequencies and telephone numbers listed in AC-U-KWIK. While I know these are automated weather reporting systems at airports, what exactly is the difference between the two systems?

AWOS (Automated Weather Observation System) units began to be deployed at airports in the 1970s. This equipment continuously monitors on-site meteorological conditions at airports, and a computer generated voice description relays this info to pilots via radio or by phone. The simplest AWOS stations simply report barometric pressure and altimeter setting. AWOS-III (level three) systems are the most prevalent and add wind speed, wind direction, temperature, dew point, density altitude, visibility, cloud ceiling and current precipitation.

ASOS (Automated Surface Observation System) units came on the scene in 1991 and do everything AWOS systems can, however they are capable of more  sophisticated weather observations. They can determine type and intensity of the precipitation, and also can better detect thunderstorms, lightning, fog, haze or smoky conditions. While these units continually broadcast conditions to pilots, they are also used by the National Weather Service for national forecasting; so a few of these ASOS stations are located at non-airport locations such as the Baltimore Science Center and New York City’s Central Park.