They are often generated as air flows over mountains and are common east of the Rocky Mountains. The clouds appear anchored to the mountain. These clouds form when the air is stable downwind of the mountain, the wind flows over the mountain in a wave-like pattern, and lenticular clouds are often generated in the ascending air over a mountain. On the descending branch of this mountain generated wave, air is compressed, warmed and the cloud evaporates as the relative humidity decreases. This flow pattern is called a mountain wave.
Lenticulus clouds can form whenever the air flow undulates in a regular pattern.
While the clouds appear smooth, the vertical motions are very strong and turbulent. Aircraft avoid flying at the altitude at which lenticulus clouds form. Mammatus Mammatus cloud derive their name from their pouch-like appearance. Mammatus clouds often form on the bottom of a spreading anvil associated with a large, active cumulonimbus. Mammatus clouds often follow, within minutes to an hour, the most active stage of a cumulonimbus.