NorthwestDecember 23, 2019

Kimberly Cauvel Of the Skagit Valley HeraldTNS
This photograph by Daniel Thomas shows mammatus clouds.
This photograph by Daniel Thomas shows mammatus clouds.Skagit Valley Herald

MOUNT VERNON, Wash. — A rarely seen cloud formation was spotted Tuesday over parts of Skagit County as the region braced for several days of rain and snow.

Courtney Obergfell, a meteorologist at the National Weather Service’s Seattle office, said the ominous clouds are called mammatus and occur when cold air sinks, forming pouches beneath more common clouds, often those bearing rain.

Multiple Skagit Valley Herald readers snapped photos Tuesday morning of the unusual clouds that looked rumpled and glowing — almost like bubbling pastry dough — over Burlington and Mount Vernon.

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The National Weather Service defines mammatus clouds as “rounded, smooth, sack-like protrusions hanging from the underside of a cloud.”

Little information and few examples of the rare clouds are available on websites of the weather service and its parent organization, the National Oceanic and Atmospheric Administration.

Ron Lehman of Friday Harbor recognized the clouds as mammatus after seeing them over his home years ago, and identifying them at that time using a National Audubon Society field guide for North American Weather.

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