Definition
ASOS and AWOS are networks of automated weather stations located at airports that continuously measure surface weather conditions and broadcast the results to pilots. They report items such as wind direction and speed, visibility, cloud height, temperature, dew point, altimeter setting, and precipitation. Reports are transmitted by a dedicated radio frequency and, at most sites, by telephone. ASOS is the more capable system jointly operated by the FAA, NWS, and DoD, while AWOS is a family of FAA-operated systems with varying levels of capability (AWOS-A, AWOS-1, AWOS-2, AWOS-3, etc.).
Plain English
Automated weather stations at airports that constantly measure local conditions and broadcast them so pilots can hear current weather before takeoff or landing.
Context Anchor
Pilots use ASOS/AWOS before departure, while en route, and before arrival to check the latest reported weather at an airport.
Derivation
Both names describe what the systems do. 'Automated' means the readings are taken by machines rather than a human observer. 'Surface' (ASOS) emphasizes that readings are taken at ground level, distinguishing them from upper-air observations. The earlier human weather observer at an airport has largely been replaced by these automated stations.
Why Pilots Care
The data directly affects go/no-go decisions, instrument approach minimums, and runway selection, especially when fog reduces visibility below visual flight rules limits.
Grounding Statement
On a foggy morning, ASOS/AWOS gives the pilot a current local report instead of relying on a general weather picture for the area.
Intuition Check
Do not treat ASOS/AWOS as a forecast. It reports current observed conditions at or near the airport, not what the weather will be later.
Example Sentence 1
Before departing the uncontrolled field, the pilot tuned the AWOS frequency and noted that visibility had dropped to one mile in fog.
Example Sentence 2
The ASOS/AWOS report showed one-quarter mile visibility in fog, so the pilot elected to file an IFR flight plan instead of departing VFR.