WEATHERVIDEOHD.TV / SCIENCE PHOTO LIBRARY WEATHERVIDEOHD.TV / SCIENCE PHOTO LIBRARY
Timelapse footage of a classic roll cloud, showing the rotation from which it takes its name. Roll clouds form when cool air from a storm cloud's downdraft hits the ground and spreads out, undercutting warmer air and raising it to a level at which condensation occurs. Filmed in the USA on a spring afternoon.
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