Definition
Ground-based automated weather stations installed at airports that continuously measure local surface weather conditions — including wind direction and speed, visibility, sky condition, temperature, dew point, altimeter setting, and precipitation — and broadcast the report over a dedicated radio frequency and/or telephone line. ASOS is the joint FAA/NWS/DoD primary surface weather observing network in the United States; AWOS is an FAA-commissioned system, often found at smaller or non-towered airports, with several configurations (AWOS-A through AWOS-3) reporting different levels of detail.
Plain English
An automatic weather station at an airport that constantly measures the weather and reads it out loud on a radio frequency or phone line, so pilots can hear the latest conditions before landing or taking off.
Context Anchor
A pilot commonly checks ASOS/AWOS while planning the descent and approach to learn the latest weather at the destination airport.
Derivation
‘Automated’ means it runs by itself with no human observer. ‘Surface’ means the weather at airport level, not aloft. ‘Observing’ here means measuring and reporting — the same sense used in ‘weather observation.’ Together: an unmanned station that watches the weather at the field and tells you about it.
Why Pilots Care
Provides the only real-time weather information available at many non-towered airports, directly affecting runway choice, approach minimums, and landing decisions.
Intuition Check
ASOS/AWOS is not a forecast. It is an automated report of the weather being observed at or near the airport at that time.
Example Sentence 1
About 40 miles out, the pilot tuned in the destination ASOS and copied the wind, altimeter setting, and ceiling before briefing the approach.
Example Sentence 2
AWOS reported visibility at three miles, so the pilot elected to fly the GPS approach instead of the visual.