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Mass: Mysterious 'Stink Fog' Has Subsided, But Morning Fog And Mild Temps To Linger

Tim Durkan

The fog will likely stick around for a few more days, thanks to “a huge inversion,” an upside-down pattern of air temperatures that trap morning fog, says KPLU weather expert Cliff Mass.

“We have extremely warm air over us — summertime-warm air [at] freezing level, 10,000 feet — but we have cold air trapped at the surface,” Mass said. “And that cold air acts as a lid.”

Below that lid, fog is lingering, as we saw on Friday morning.

“Hopefully it’ll burn out as we get later in the day,” Mass said, predicting a partly cloudy start to the weekend with temperatures getting up near 50. “Not a bad day, and gets quite warm if you go up.”

Clouds On The Horizon This Weekend

Late Friday and early Saturday, Mass says a weak disturbance will come through, bringing the likelihood of light sprinkles and some clouds with temperatures in the upper 40s.

“So nothing exciting. No snow in the mountains; just a little bit of light rain and a lot of clouds,” Mass said.

Sunday’s outlook appears similar with another weak front coming in, but this one heading south of us.  

“We have what’s called ‘flow splitting,’” Mass said. “So most of the atmospheric upward motion that produces clouds and precipitation will go into Oregon.”  

Western Washington should be cloudy to partly cloudy, with temperatures in the upper 40s and maybe a 20 to 30 percent chance of a few sprinkles, especially in the south part of the state, Mass said.

On Monday and Tuesday, another ridge will develop with high pressure building aloft, Mass said, “so precipitation gets cut off and we’ll probably see some partly cloudy skies,” and temperatures will likely reach around 50.

No Good News For Mountain Snow Pack

Ski areas that had been eking by with marginal snow got hit with warm rain again this week, and there’s no sign of improvement in the near term forecast.

“They’re not going to get any relief this weekend.” Mass said. “There will not be any significant new snow at least till the end of next week.”  

The Mystery Stink Has Finally Subsided

The stench that accompanied the morning fog on Wednesday seems to be a thing of the past. Many people described aromas of manure, tide flats or pulp mills filling the air over Seattle, Bainbridge Island and Paulsbo.

Mass investigated the source of the "stink fog" and said the most-likely cause was the receding floodwaters east of Seattle and airflow over soils that were drying out afterward, though he said it’s still a bit of a mystery.

“The metrological conditions were good to keep something in, but we’re not sure where it came from,” Mass said. 


The weekly KPLU feature "Weather with Cliff Mass" airs every Friday at 9 a.m. immediately following BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KPLU Environment Reporter Bellamy Pailthorp. Cliff Mass is a University of Washington Professor of Atmospheric Sciences, a renowned Seattle weather prognosticator, and a popular weather blogger. You can also subscribe to a podcast of “Weather with Cliff Mass” shows.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to