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One Last Day Of Clear Skies And Sunshine, Then Big Rain Ahead

Tim Durkan
Tim Durkan Photography
A September sunset on Puget Sound with the Olympic Mountains in the background.

Enjoy one last day of summer-like weather in the Puget Sound region on Friday, but brace yourselves for a big change on Saturday. Knkx weather expert Cliff Mass says the wettest weekend of the summer is on its way. And it will remain rainy and cool for the foreseeable future.

‘Glorious’ Friday

“Today is the last really nice day for a while,” Mass said of Friday. “It’s going to be glorious,” he said, with temperatures in the mid-70s and plenty of sun.

“Today’s the day to get out; believe me. Because then this weekend, the jetstream, that current of strong winds over the Pacific which has been moving southward for a while, is about to come right into us,” he said.

He says that will bring in the strongest weather system we have seen here in months.

Jet Stream Hits Saturday

Overnight from Friday into Saturday, expect big rain to come in fast.

“I expect Saturday to be a washout for much of the region,” Mass said. “We’re talking about the mountains getting a few inches of rain – this is not insignificant – and maybe a half an inch down in the lowlands. So, a major rain event.”

Showery And Cool On Sunday

On Sunday, Mass says the jet stream will be “kind of hanging around” but its influence will not be as strong. “It’s going to kind of back off a little bit in terms of rain.” He says this means there will be some showers and temperatures will stay down in the 60s, likely the lower 60s. The only significant rain will be in the mountains.

“So if you’re taking that hike on the windward side of the Cascades, it may not be great, especially early on Sunday,” Mass said.

Cooler Next Week

Next week, Mass says expect more of the cooler and showery regime.

“We have a pattern that is not warm. We’re not going to have major systems coming in, but there could be showers on Monday and there will be other weaker systems coming in during the week.”

He says there will probably be at least one or two days where the sun will come out and temperatures will rise into the upper 60s.

“But it’s going to be a completely different regime as we cross over this weekend into next week,” Mass said.

To hear the forecast along with a discussion of thehuge diurnal range in temperatures typical at this time of year, you can click on the “play” icon at the top of this post.

The weekly knkx 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 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 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