Definition
Sudden, sharp turbulence that occurs in cloudless air, typically at high altitudes near the jet stream where fast-moving air shears against slower-moving air. Because there are no clouds or visible weather, it cannot be seen and is rarely detected by onboard weather radar.
Plain English
Bumpy, rough air that hits without warning in a clear sky. Nothing on the windscreen or radar tells you it is coming — the aircraft just suddenly shakes or jolts.
Context Anchor
Seen in weather briefings, pilot reports, and high-altitude flight planning, especially near strong winds aloft or jet stream areas.
Derivation
The name describes exactly what it is: turbulence in clear air. The phrase exists because pilots needed a way to distinguish this kind of rough air from the turbulence normally associated with visible weather like thunderstorms or clouds.
Why Pilots Care
It can produce sudden violent updrafts and downdrafts capable of injuring passengers and crew or exceeding aircraft structural limits.
Analogy
It is like hitting a rough patch on a road that looks smooth from a distance. Nothing obvious warns you before the ride suddenly gets rough.
Grounding Statement
A pilot may be flying in blue sky with no clouds ahead and still enter air that suddenly shakes the airplane.
Intuition Check
“Clear air” does not mean calm air. It means the turbulence is occurring where there may be no visible cloud or storm warning.
Example Sentence 1
The crew turned on the seat belt sign after a PIREP reported moderate clear air turbulence near the jet stream at FL360.
Example Sentence 2
Forecasts help pilots plan routes that avoid the strongest clear air turbulence near the jet stream.