Unclouding the mystery of lenticular clouds
You may have once witnessed one of these gorgeous clouds before in person, or maybe you've seen them in photos or in movies. They hold a cloak of mystery over the tops of mountains, but despite their magical appearance, there is a scientific reason for how these saucer-like clouds appear so often at the tops of high peaks. They're called lenticular clouds, and they need just the right conditions to form, conditions often found around topographical formations like hills and mountains.
To form, lenticular clouds need a current of moist air forced upward, as happens when air travels up the side and over the top of a mountain. The moisture condenses to create a cloud, and when the moist air reaches the crest of the mountain, a wave pattern, or atmospheric standing wave, is created in the air flow. As the air hits the crest of the wave and moves downward, the cloud formed at the crest may evaporate, forming the cloud which sits at the very crest of the wave. Lenticular clouds are a bundle of movement, yet they look stationary. That’s because the flow of moist air up one side of the mountain replenishes the cloud on the windward side while the dry air flowing down the other side dries the cloud out on the leeward side. When formed above a mountain, it can seem to hover for hours or even days until weather conditions change.
They don't have to have a mountain to form, but it helps. You can find out more about the how and why of lenticular clouds here: How lenticular clouds are formed.
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