"Undulatus Asperatus" Clouds Help Create Fascinating Video

Undulatus Asperatus clouds over Cedar Rapids, Iowa
a few years ago. The clouds look very scary
but do not cause severe weather.  

"Undulatus Asperatus" sounds like the name of a horrible, rare, disease, doesn't it?

But it's a fairly rare type of cloud. It actually wasn't identified as a type of cloud until 2009. (Unlike the clouds we've long been familiar with. You know, cumulus, cirrus, that type of thing.)

Undulatus Asperatus clouds look dark and menacing as they move across the sky. They make it look like the Worst. Storm. Ever. is coming.

The name of the cloud roughly means "very turbulent, violent form of undulation," says National Geographic, which makes the cloud seem ever more scary.

But these clouds don't signal dangerous weather. They seem to be most often seen across the Great Plains of the United States. They usually appear in the morning or midday near weakening thunderstorms.

Undulatus Asperatus clouds have never been known to cause severe weather.

A video that's gone viral in the past week or so shows a time lapse of Undulatus Asperatus clouds over Lincoln, Nebraska in July.  They look otherwordly, and probably scared a few Nebraskans.

But the video is mesmerizing. Watch: