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Cooler Northwest Weather Has Arrived – And It’s Igniting Washington Wildfires

Tim Durkan
Tim Durkan Photography
Typical Seattle weather, in April 2018.

Cloudy skies, cool marine air and patches of drizzle greeted folks in the Puget Sound region Friday morning for a second day.

The filtered light and soft cloud layer signaled a return to more typical weather after nearly three months of dry skies and above-normal temperatures. The days of temperatures in the 90s are done, says KNKX weather expert Cliff Mass, a professor of atmospheric sciences at the University of Washington.

Cooler Weather Is Here To Stay

“It’s a tremendous change,” Mass said.  “I had some rain around my house this morning.”

But it’s pretty much right on schedule, as the warmest temperatures of the year generally happen in the last week of July or first week of August.

“As we get later into August, the weakening sun is going to cool us down, inevitably,” he said.

The computer models meteorologists use to predict the weather further out indicate that the cool will continue. Mass says they are not showing any major heat waves or offshore flow that would cause temperatures to surge into the upper 80s and 90s.

“The sun is starting to weaken. The days are getting shorter. The nights are getting longer,” Mass said. “And eventually, that has an impact.”

Sunny Weekend Starts Saturday Afternoon

Expect cloudy weather on Friday with temperatures in the lower 70s at the most, he says, with only a possibility of a few sun breaks later in the day.

“As we go into the weekend we’re going to see improvement,” Mass said.

He says the trough of low pressure aloft that brought in the cool weather Thursday and Friday will move through as a ridge of high pressure slowly builds in.

“So Saturday’s going to be a step up – partly cloudy in the morning, but temperatures getting up to the mid-70s, maybe upper 70s in a few places.

"But on Sunday as the ridge builds over us, I expect temperatures climbing probably into the lower 80s – and plenty of sun,” Mass said.

The only chance of showers on Saturday and Sunday will be in the mountains, with a possibility of some weak thunderstorms near the Cascade crest, he said.

And then as we get into next week, it looks like Monday and Tuesday should be fairly warm – temperatures in the lower 80s.

“So, you know, we have this cool period associated with an upper level trough, but that’s going to change as we get into the weekend,” Mass said.

Why Cooler Weather In The West Stokes Fires In the East

Ironically, Mass says the cooler weather is not helping firefighters in Washington State; it has actually caused fires to ignite and spread over the past few days. And this is also pretty typical.

The cloudy weather here is linked to winds and thunderstorms east of the mountains, because there’s a big difference in pressure on either side of the Cascade divide, and that accelerates winds.

“So as we get cool, the winds pick up from the Cascade Crest down into eastern Washington along the eastern side of the Cascades," Mass said. “And in fact, (on Thursday) we had winds gusting up to 40-50 miles per hour in some places in eastern Washington.

“So you have the trough that produces lighting that gets fire started. And then the trough also produces this big change in pressure that creates very gusty winds that allows these fires to explode."

To hear the full conversation, including Cliff’s update on air quality and smoke from the wildfires, 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, anda popular weather blogger. You can also subscribe to podcasts of Weather with Cliff Mass shows, viaiTunes or 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