What’s this cloud?

On two occasions, I’ve observed these particular clouds, first when we drove to California late April, and this morning as we were out on our morning walk. 

At first, I thought it was a cirrus cloud, but cirrus clouds are detached clouds in the form of white, delicate filaments, mostly in patches or narrow bands. They may have a fibrous, hair-like, and sometimes silky sheen appearance. 

Since I don’t know much about clouds, I had to do some research and found out that based on the distinct smooth, lens-like, and somewhat aerodynamic shape of that cloud, it was a lenticular cloud (technically classified as Altocumulus lenticularis). These clouds are famous for looking like flying saucers, pancakes, or lenses. 

The one I photographed has incredibly clean, smooth edges, which happens when the air is moving in a stable, consistent flow (that day was quite windy). The lenticular clouds typically form when moist air is forced upward over a mountain range or large hill. As the air drops back down, a standing wave is created on the downwind side of the mountain (similar to water rippling over a pebble in a stream). 

If the temperature at the crest of the wave drops to the dew point, the moisture condenses into this beautiful, stationary cloud. Even though the cloud looks like it's just sitting there perfectly still, air is actually constantly flowing through it, in fact, condensing into a cloud as it hits the peak of the wave and evaporating as it moves down the other side. 

​These clouds are a favorite for photographers, but pilots generally give them a wide berth because they indicate strong, bumpy turbulence hiding in the upper atmosphere.