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Mini Heat Wave Ends, Western Washington Suddenly Transitions To Cool Fall

Lindley Ashline
Seattle from the Bainbridge Island ferry

Seattle saw the mercury hit 86 degrees on Thursday, breaking another daily heat record as people all over the Puget Sound region donned their shorts and sandals and experienced one last taste of summer-like weather.

“Extraordinary,” said KNKX weather expert Cliff Mass of Thursday’s heat.

“Seattle got to 86. But other places -- Olympia and around Everett -- they got into the upper 80s, a few low 90s.”

Don’t get used to it. As of Friday morning, the weather had already changed, with temperatures dropping fast. And Mass says they won’t be going up again anytime soon.

“I hate to tell you that this is the last time we’re going to see 80 degrees, probably until next April or May” said Mass, who teaches Atmospheric Sciences at the University of Washington. “I mean this is it.”

He says computer forecast models are predicting a cool-down that will last all weekend long. And, as many people likely noticed, it started last night.

“The marine air surged in. A modest Pacific front is now passing through western Washington. And so that’s bringing some rain,” he said.

Friday’s temperatures will only get into the 60s.

“So, a huge cool down. We’re talking about a 20-degree cool down,” Mass exclaimed.

The rest of the weekend, he says expect showers and clouds, with temperatures only getting up into the lower 60s.

“Not only will we have some light rain all over the place, but we’ll have a Puget Sound convergence zone somewhere between Seattle and Everett that will enhance the precipitation. And more precipitation on the western side of the Cascades,” Mass said.

And that’s just the beginning, he says. The transition to fall weather is off and running now for real.  

“I’ve looked at the long-term computer models and it’s going to be cool -- temperatures in 60s and even upper 50s – as far as I can see,” he said.

Then, after the end of next week, Mass says it’s too late to get warm again. The sun’s heat is weakening very rapidly.

“Once you get into October 10th or something like that, the chances of getting to 80 go down to virtually zero,” he said.

“So, say goodbye to 80, it’s over.”

To hear the full conversation, including a discussion of how drinking straws can teach us about atmospheric pressure (part of Cliff’s Weather 101 curriculum,) you can click on the 'play' icon at the top of this post. 

Weather with Cliff Mass airs at 9:02 a.m. Friday, right after BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX 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 podcasts of Weather with Cliff Mass shows, via iTunesor Google Play.

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