Lenticular Clouds

Lenticular Clouds 

In this photo there are two clouds stacked up into one beautiful and striking lenticular cloud on top of Mt. Rainier, US.

Normally, air moves much more horizontally than it does vertically. Sometimes, however, such as when wind comes off of a mountain or a hill, relatively strong vertical oscillations take place as the air stabilizes. 

The dry air at the top of an oscillation may be quite stratified in moisture content, and hence forms clouds at each layer where the air saturates with moisture. The result can be a lenticular cloud with a strongly layered appearance.

Due to their shape, they have been offered as an explanation for some Unidentified Flying Object (UFO) sightings.