WEATHERVIDEOHD.TV / SCIENCE PHOTO LIBRARY WEATHERVIDEOHD.TV / SCIENCE PHOTO LIBRARY
Timelapse footage of a fast-growing cumulus cloud with a pileus cloud at its top. Pileus clouds appear as wispy horizontal caps, and form as the rising air in the cumulus clouds pushes moist air upwards, causing it to condense. They are indicative of powerful updrafts, and therefore a good sign of an impending storm. Filmed in Colorado, USA, in summer.
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