Rare 'roll cloud' snakes over Fort Resolution, N.W.T.

Residents of the community of Fort Resolution, N.W.T. were treated to a rare sight Saturday evening — a unique "roll cloud" that left onlookers confused and amazed.

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Lorraine Villeneuve sent photos and video of the cloud to CBC North, which appeared over the community just before midnight on May 28. 

A low-lying formation, the cloud appeared in the shape of a long tube, stretching out over the N.W.T hamlet and into the horizon.

• See Lorraine Villeneuve's video of the roll cloud on CBC NWT's Facebook page

CBC North meteorologist Ashley Brauweiler says that the formation is a "roll cloud," which typically appear before thunderstorms. 

"It's a rare cloud that forms in front of an approaching thunderstorm, or cold front," she explained. "This causes a temperature inversion, or warm air over cold."

As the warm air rises, Brauweiler explains, it then cools and condenses, forming the cloud. Changes in wind speed at the top of the cloud create the rolling motion, which cause a tube-like formation across the sky.

Villeneuve says that she didn't notice a thunderstorm that night, but conditions were windy and it rained shortly after she spotted the cloud formation.