What was with the funky 'line' cloud over Puget Sound Tuesday?

Jerry Erickson

SEATTLE -- Tuesday evening not only brought a gorgeous sunset, but also a rather peculiar looking cloud that piqued the interest of several residents out enjoying the evening.

"(Tuesday) night just before sunset at our house in Shoreline..., I noticed that there was this very dramatic line of clouds across the entire sky from west to east, with the sky covered in clouds to the south of the line," wrote Jerry Erickson. "To the north of the clouds it was clear. Later the cloud formation moved to the south. I have never seen something like this before with such a clean edge of clouds."

Indeed you can in photos the dramatic edge to the clouds. What was up?

"It seems to have been produced by the interaction of a weak upper vortex and the Olympics," says University of Washington Professor Cliff Mass.

You can kind of see this play out on the visible satellite imagery. Watch the rotating clouds come from the Strait of Juan de Fuca and then some clouds form downstream of the Olympics as this little system reaches the mountains:

And here's how it played out in time lapse video:

No rain or anything came from the cloud, just a neat little addition to the sunset.

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