What looked very much like a mushroom cloud formed over Seattle and triggered double-takes everywhere Wednesday morning.
"What the heck kind of cloud formation (I hope) was this?" KING-TV viewer Kathy Fisher asked on the station's Facebook page.
Fisher took a photo during a traffic jam on Highway 99, KING said.
Karla Freeman Johnson also saw it from the West Seattle bridge and snapped a photo as well.
So, what was this eye-catching phenomenon?
"It looks like remnants from a low deck of clouds," KING-TV Chief Meteorologist Jeff Renner said. "It's apparent these are low clouds from the proximity to the buildings and the very flat tops. Probably 2,000-3,000 feet at most above the ground. That argues against enough depth to produce rain showers such as could produce a shaft. I believe you're seeing a release of steam or exhaust from a ground-based plant rise into the remnant low clouds, producing the 'mushroom' shape."