Altocumulus Lenticularis

Getting to know the 10 main cloud types is the first step in becoming an accomplished skywatcher. However, in mountainous regions such as the Rockies in North America and the Alps in Europe, there is a common type of cloud, called a lenticular cloud, not seen in relatively flat countryside.

Lenticular clouds form only over mountain peaks. Sometimes, they look like a stack of giant dinner plates or a formation of huge flying saucers. They can also look like a huge lid or a tall hat hovering above the mountains. The cause is quite simple. Winds carrying air over a mountain rise up one side, cooling on the way. Moisture in the air condenses to form a cloud. When the air moves down the other side of the mountain, it warms up. The droplets in the cloud then turn back to water vapour because warm air can hold more vapour than cool air.

Since winds are constantly blowing over the mountain, the cloud is continually renewed. It therefore appears to remain in position, since it marks the spot where air is cooled into condensation. Lenticular clouds are not always seen over mountains. The air flow must be smooth, rather than turbulent, to allow the beautiful layer-cake structure to develop.

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