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| | Earth on Feb 17, 2014
Lenticular cloud, by Chris Walker, 2008

Lenticular cloud, by Chris Walker, 2008
These lens-shaped clouds are often mistaken for UFOs. Here how they form, plus the best in photos and video.

Here are seven photos and a video of beautiful lenticular clouds. EarthSky friends on Facebook and Google+ took the photos in various places around the world. These lens-shaped clouds typically form where stable moist air flows over a mountain or a range of mountains. When this happens, a series of large-scale standing waves may form on the mountain’s downwind side. If the temperature at the crest of the wave drops to the dew point, moisture in the air may condense to form lenticular clouds. As the moist air moves back down into the trough of the wave, the cloud may evaporate back into vapor. So lenticular can appear and disappear relatively quickly. Plus they’re not familiar to people who live in low-lying or flat terrain. And, just to confound things, lenticular clouds have also been known to form in non-mountainous places, as the result of shear winds created by a front. For all of these reasons, lenticular clouds are often mistaken for UFOs (or “visual cover” for UFOs). Enjoy the photos! Thank you to all who posted.

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