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Fall Begins After Driest And Warmest Summer Ever Recorded At Sea-Tac

Tim Durkan
Tim Durkan Photography
A late summer walk on the beach in Seattle, September 2017.

Residents of the greater Puget Sound region have already been feeling the transition to fall with a shift down to lower temps and more clouds last week. But Friday marks the official end of summer, with the autumnal equinox on the calendar.

“Autumn starts at 1:02 pm,” said KNKX weather expert Cliff Mass. “You know, maybe you’ll have some kind of ceremony for that,” he joked, adding that Friday’s weather will fit the bill, with scattered clouds in the morning yielding to mostly sunny conditions in the afternoon and temperatures getting into the mid- to upper-60s.  

“So, very fall-ish,” he said.

Mild Weekend Ahead

He says the days ahead will bring much of the same, with the best weather of the weekend coming on Saturday.

“A ridge of high pressure will build over us, temperatures will surge to around 70 here in Seattle,” Mass said. “Plenty of sun, so a really nice day.”

Then, on Sunday, that ridge of high pressure will get “damped down.”

“We have what we call a ‘dirty ridge,’ so some clouds are going to start moving in Saturday night and Sunday,” he said.

That means clouds are likely Sunday as well as possible sprinkles along the coast.

“But here in Seattle it should be dry,” Mass said. 

Monday and Tuesday, with the ridge relatively weak, he says the sprinkles from the coast will continue and likely push into northern Puget Sound and Northwest Washington.

And temperatures early next week will likely warm up, again reaching the mid-60s, Mass said. By mid-week, temperatures are expected to surge up again into the lower 70s.

“So a little bit of up and down, but no significant weather at all and maybe just a few sprinkles at a few points.”

It’s Official: Summer 2017 Is Seattle’s Driest And Warmest

The scant rain has been a theme of the past summer. Mass says it is in fact going down as the driest summer in Seattle history.

That’s measured by the calendar summer, from June 21to Sept. 21, looking at precipitation recorded at Sea-Tac Airport. This year charted the lowest number ever, with a 3-month total of just 0.52 inches.

“So there’s no summer that compares to this if we look at the observations at Sea-Tac,” Mass said.

“And in fact if we even look back even further, using the downtown Seattle observations, it’s still the driest summer. So we are all the way. This is as dry as it gets,” Mass said.

The National Weather Service also noted that the summers of 2013, 2014 and 2015 were among the top 5 driest years on record.  

And 2017 is also going down as warmest summer on record, with a mean temperature of about 78 degrees.

“And we’re just about .1 degrees warmer than the runner up,” Mass said, which was in 1967.  The National Weather Service officially recorded that as a tie.

“So it’s a little close to call, but, we’re certainly in one of the warmest summers we’ve ever experienced here,” Mass said.  

Mass says despite the the past season's record warm and dry weather, winter is expected to be wetter and cooler than average, because of the recent switch to a La Niña watch.

To hear the full conversation, including a discussion of what kind of weather La Niña normally brings to the Pacific Northwest, 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 iTunes or Google Play.

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