Seattle's weather is about to revert to its more normal, pleasantly mild and occasionally moist summer pattern.
Rain in the weekend forecast should wash out the gritty smoke from British Columbia's wildfires that has plagued the region for more than a week now. The precipitation will also put an end to the long dry spell the city has experienced.
“Everything changes this weekend – it’s going to be amazing,” said KNKX weather expert Cliff Mass, a professor of Atmospheric Sciences at the University of Washington, adding that Friday will be the last really warm day for a while.
Already Cooling Down
“It won’t be as hot as we’ve seen,” he said of Friday’s weather. “But temperatures will get up into the lower 80s – still above normal – and that pesky smoke… it’s going to hang around for a little bit more.
“But everything changes over the weekend,” Mass said.
He says an upper level trough of lower pressure is moving toward the region now and the ridge of high pressure that caused the long spell of heat and smoke is starting to move out.
Clouds and Showers On Saturday
“So as the upper level trough approaches tonight and tomorrow, the winds are going to increase from the west, the smoke is going to be blown away, and we’re going to see an increase in clouds – quite a bit of clouds tomorrow,” he said of Saturday’s forecast.
“And even some sprinkles. Not the heavy stuff, but there will be some showers during the day,” Mass said. He says eastern Oregon will even get some thundershowers on Saturday.
Biggest Shift On Sunday
“Then, the main trough comes in on Sunday. And I think Saturday night – Sunday morning, there may be some real rain. Maybe a tenth of an inch here in the Puget Sound area and maybe as much as a half an inch along the coast,” Mass said. “So, this is the historical change: The first rain of the season.”
He says that trough moving through will also bring cooler air with it, pushing temperatures back into the more normal range for this time of year.
“So next week, temperature will get up into the mid-70s – no smoke and it will just be back to what we enjoy here of Puget Sound, western Washington summer.”
Dry Spell Ending With New Record
On Monday, the region tied the record for 51 consecutive days with no measurable rain at Sea-Tac Airport. Mass says with rain coming in Saturday, the new record will be left at 55 or 56, depending on how much comes down over the weekend and where.
“But we have to be careful about this,” Mass cautioned. “I mean, that’s a fun record, but it was really just Sea-Tac. The rain occurred to the north and south of Sea-Tac, and if you look at the total rain over the summer, we’re really not that far behind.”
Mass says the rainfall totals for the summer put the region about an inch and a half below what’s normal at this point.
“And a lot of that’s going to be made up this weekend,” he said. “So, we could end up with normal summer rainfall before it’s over.”
To hear the full conversation, including a discussion of how the B.C. wildfire smoke has been affecting regional temperatures, 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.