The official start of summer has not yet arrived, but folks in the Pacific Northwest will feel like it has this weekend. KPLU weather expert Cliff Mass says the mercury will rise into the 90s in many parts of Washington, bringing unseasonably hot weather to the region.
“In fact, some places south of us will get to 100,” said Mass, a professor of atmospheric sciences at the University of Washington.
'Just Perfect' on Friday
He says Friday’s weather will be a bit milder, as a weak disturbance moves through and clouds linger through a warming period.
“But probably temperatures will only get into the upper 70s in most of the Puget Sound area,” Mass said, adding that it will be “just perfect.”
Over the weekend, he says a ridge of high pressure will build above us, bringing in a lot of warmth.
“But it’s not going to last forever,” said Mass. “It’s just the weekend.”
He says there will be substantial cooling on Monday.
Temps Rev Up Saturday And Sunday
Saturday, as the ridge builds, there will be warming aloft. That will combine with what’s known as a thermal trough - an area of low pressure that hugs the western side of the Cascades – that will move in from the south. Those dynamics combined with higher pressure to the east will bring in offshore flow, which typically causes warming.
Mass says that will push temperatures to 100 in Portland on Saturday.
“That’s pretty amazing stuff, isn’t it?” Mass said.
In the Puget Sound region, he says it won’t be quite as warm, because the trough to the south will bring in northerly winds that will cool the area.
“So Saturday, I expect temperatures only – only – getting up to the low 80s here around Seattle and the immediate vicinity,” he said.
On Sunday, the warming dynamics really rev up.
“Portland will again get to 100,” Mass said. “They could be 102, 103 – just amazing stuff.”
In the Seattle area, he says the positioning of the thermal trough means not quite as hot, likely into the upper 80s.
Too Hot? Head For The Water
“But if you get away from the water ... the temperatures in North Bend, those kind of places, will get up into the low 90s. And Olympia could be mid-90s,” he said.
“It will get into the 90s rapidly if you get south and east of [Seattle],” Mass said.
He said a cooler spot on Sunday will be northwestern Washington.
“Temperatures probably won’t get much above 80 there and it will really cool down on Sunday along the coast,” Mass said.
A Short-Lived Heat Wave
He cautions this heat wave is not the start of a trend or a harbinger of a hot season ahead. It’s temporary, due to that ridge of high pressure.
“This ridge is very transient. It’s going to start moving past us Sunday night and Monday. And we’re going to get what we call a marine push,” he said. “So Monday is going to be much cooler – temperatures probably won’t get above 80 in Seattle on Monday and it will be even cooler on the coast and in northwest Washington.”
Still, he says, the weekend will be remarkably warm in many parts of the state.
“And some places will break daily records,” he said.
He says next week, it looks like the weather will return to its normal pattern for this time of year.
“Once we get this marine air coming in, temperatures will drop back into the 70s and 60s,” Mass said.
For a discussion of the dramatic collapse of this year’s very strong El Nino and the likelihood of a La Nina for the coming winter, you can click on the “play” icon at the top of this post.
The weekly KPLU 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 KPLU 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.
