Definition
A setting on airborne weather radar that increases the receiver's sensitivity so it can detect very light returns, such as faint precipitation, light moisture, or large insects, that would not be visible in the standard weather mode.
Plain English
A high-sensitivity setting on the weather radar used to spot weak returns the normal weather setting would miss.
Context Anchor
Seen in aviation weather discussions when interpreting radar observations during mostly dry or very light weather conditions.
Derivation
Named for its purpose: detecting faint returns in air that looks 'clear' on the normal radar setting. The mode is most useful when the sky appears empty but the pilot wants to confirm whether anything is actually there.
Why Pilots Care
Reveals hidden hazards such as light rain, virga, or turbulence that could affect flight safety before they become visible.
Analogy
It is like turning up the sensitivity on a microphone in a quiet room. You may hear faint sounds you would otherwise miss, but you have to listen more carefully and give it more time.
Intuition Check
Clear air mode does not mean the radar sees perfectly through empty air. It means the radar is set to look for very weak returns when little or no precipitation is present.
Example Sentence 1
Cruising over the Gulf, the pilot switched the radar to clear air mode to check for any light returns ahead of the forecast frontal boundary.
Example Sentence 2
With the radar in clear air mode, faint returns appeared that suggested possible turbulence.