PORTLAND, Ore. — Social media was buzzing Friday morning with many people wondering why there were so many contrails. It seemed everywhere you looked, there were circles etched in the sky. Some people even called them “contrail donuts.”

So, why were there so many contrails? The explanation is simple, according to KGW chief meteorologist Matt Zaffino.

The cause of the contrails stemmed from an issue in Seattle. There was dense fog at Seattle-Tacoma International Airport Friday morning, limiting visibility to a quarter-mile at times. So, planes were in a holding pattern and more than 200 flights to and from Sea-Tac were delayed.

Portland International Airport is the backup landing site for planes heading to Seattle, so the delayed planes circled overhead in the Portland metro area.

Contrails over Portland on Nov. 8, 2019
Contrails over Portland on Nov. 8, 2019
Anna Blackwell Everett

That was the cause of the contrails. But why were they visible for so long? There’s a scientific reason for that.

Zaffino said there was high humidity at flight level Friday morning, which led to the contrails staying in place for so long.

“It’s like having a cloud in a very humid environment. It just doesn’t go anywhere very fast because the difference in vapor pressure is really, really low,” he said.

That’s why the contrails were visible for so long. If the air was dry Friday morning, we may not have seen any contrails because they would have dissipated quickly, Zaffino said.

As one viewer noted to Zaffino, the conditions allowed the sky to be the canvas for the planes circling overhead.

Contrails over Portland on Nov. 8, 2019
Contrails over Portland on Nov. 8, 2019
Lori Kellow

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