rotor cloud

rotor cloud

[′rōd·ər ‚klau̇d]
(meteorology)
Turbulent, altocumulus-type cloud formation found in the lee of some large mountain barriers, particularly in the Sierra Nevadas near Bishop, California; the air in the cloud rotates around an axis parallel to the range. Also known as roll cloud.

rotor cloud

rotor cloudclick for a larger image
A cloud that forms on the downwind side of a mountain or hill feature. A wave motion is set up on the downwind side. Moist air moving up to the crest of a wave may cool enough to form a cloud. As it sinks to the trough, the cloud evaporates. The clouds thus seem stationary even though the air is moving in waves. The turbulence is often indicated by small rotor clouds at lower levels.
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References in periodicals archive ?
It was the same briefer who told me he had been looking at the weather some more and there was what looked to be a huge rotor cloud 40 miles long stretching across my proposed route of flight.
If you see rotor clouds, this is the altitude where turbulence is the worst.
But the UFOs were lenticular and rotor clouds -created by air being squeezed over mountains.
The presence of ridge-line cap clouds, chewy-looking rotor clouds in the lee and your classic wave lenticulars means only one thing: turbulence ahead.