Check out this cool cloud. It's a type of stratocumulus cloud called a lenticular cloud.
They tend to form over higher elevations, especially over mountains where conditions are just right to give it a UFO appearance.
Sometimes during a sunrise or sunset, when the light hits the clouds just right, these cloud formations can be mistaken for flying saucers.
Lenticular comes from the Latin word meaning "lens shaped."
So how do they form? When air flows on the surface of the earth and it has moisture, sometimes it comes in contact with objects such as mountains, bridges, or buildings. These objects can disrupt the flow of the air into eddies, like whirlpools.
The circular air motions can create these lenticular cloud formations.
They are not very common, but we do see them from time to time here in Arizona, like this one spotted May 15, 2016 over Flagstaff. (Thanks to Susan McCormick for the picture!)