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9 scary images of shelf clouds

By: Russell McLendon on Oct. 5, 2011, 9:02 a.m.
Shelf cloud over Hampton, Minn.

Photo: Jerry Huddleston/Flickr

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Hampton, Minn.

A UFO isn't beaming up this neighborhood in Hampton, Minn.; that's a shelf cloud, spotted south of the Twin Cities on June 25, 2010.

And the otherworldly blue glow? That's a "glow discharge," according to Cornell atmospheric scientist Mark Wysocki. It can occur when a thunderstorm is close to the ground, creating a large "surface charge density" for a long, slow-burning lightning strike — similar to how an electrical charge illuminates suspended particles in a fluorescent light bulb.