ROLL CLOUD

(Some times called Rotor Cloud), A turbulent altocumulus-type cloud formation found in the lee of some Iarge mountain barriers, particularly in the Sierra Nevadas near Bishop. California. The air in the cloud rotates around an axis parallel to the range. Also sometimes refers to part of the cloud base along the leading edge of a cumulonimbus cloud: it is formed by rolling action in the wind shear region between cool downdrafts within the cloud and warm updrafts outside the cloud.