Definition
Sudden, often severe turbulence that occurs in cloudless air, most commonly at high altitudes near the jet stream where strong wind-shear boundaries exist between fast-moving and slower air masses. Because it occurs without visible cloud cues and is not detectable by conventional weather radar, it typically arrives without warning.
Plain English
Bumpy, jolting air that hits with no warning in a clear sky, usually high up where fast and slow winds rub against each other. There are no clouds to signal it and radar cannot see it.
Context Anchor
Pilots encounter this term in weather briefings, pilot reports, and en route flying, especially during cruise at higher altitudes.
Derivation
The name simply describes what makes it dangerous: turbulence in clear air, where pilots and passengers expect smooth conditions because there are no clouds or storms to suggest otherwise.
Why Pilots Care
It produces sudden altitude changes that can injure unsecured passengers and is difficult to detect visually.
Analogy
It is like hitting a rough patch on a road that looked smooth from a distance. The surface gave you no obvious warning, but the vehicle still feels the bump.
Grounding Statement
A pilot may be flying in blue sky and smooth air, then suddenly enter a rough area because the wind around the aircraft changes quickly.
Intuition Check
Do not assume “clear air” means calm air. In this term, “clear” only means there may be no visible cloud marking the turbulence.
Example Sentence 1
The crew kept the seatbelt sign on at cruise altitude because forecasts warned of clear-air turbulence near the jet stream.
Example Sentence 2
The flight descended slightly to escape the clear-air turbulence layer.