These are turbulent altocumulus type clouds. Orographic in nature, rotor clouds are found on the lee side of some large mountain ranges. The photos of rotor clouds on the bottom of this page were taken near Portland, Oregon in the mountain range known as the High Cascades.

The air in the cloud rotates around in an axis parallel to the mountain.  Sometimes the rotation extends all the way to the ground, carrying surface dust and dirt aloft.  This causes hazardous conditions for aircraft.  It is for this reason that rotor clouds must be noted with special remarks by aviation weather observers.

Rotor Clouds above and below were photographed in Antarctica.

Rotor Clouds are often associated with Lenticular Clouds.  These beautiful clouds are also sometimes mistaken for UFO's because of their round stacked-dish shape

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Photographs above and below taken outside of Portland, Oregon, April, 2009.

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