Prepare to get wet on Saturday. But don’t lose hope. The sun will be back on Sunday, just in time for Father’s Day festivities as Northwest skies serve up a spring mix of rain and shine this weekend.
KPLU weather expert Cliff Mass says Friday’s conditions should set the tone. You’ll want to keep sunglasses as well as a rain slicker handy.
"It’s sunny from Seattle northward," Mass said. But he says conditions will start to change come Friday afternoon.
He says clouds that began over Portland and continue into Olympia are starting to move into the Puget Sound region as an upper-level trough of lower pressure moves northward, likely bringing a few light showers with it in the morning.
But Mass says the real threat for precipitation on Friday will arrive later in the afternoon, caused by instability in the atmosphere.
Friday: Cumulous Clouds And Convection Showers
"You noticed a lot of those cumulous clouds that have been puffing up during the afternoon? That’s because the air aloft is quite cold," Mass said. He says relatively strong sun heats the surface pretty intensely at this time of year, causing a large difference in temperature between the vertical air masses.
"And that causes convection," Mass said. "The atmosphere becomes unstable and we get those cumulus [clouds] – with some showers."
He expects them to rev up Friday afternoon.
"So good chance of showers later in the afternoon into the evening," Mass said.
But he says the weekend will be a study in contrasts, with two very different days.
Cool And Rainy On Saturday
On Saturday, Mass says an upper-level low will move northward, right across Western Washington.
"So I’m afraid that Saturday is going to be a mainly cloudy day with lots of showers,” Mass said. “It’s going to be pretty wet. Plenty of folks will get a tenth of an inch or so of rain. Not super winter heavy rain, but it will be raining."
That will keep the temperatures down; Mass says expect low 60s.
“That’s about it: 62, 63,” he said.
Sunny And Warm On Sunday
On Sunday, the low pressure will move past us, Mass says.
"There might be some remnant showers in the northern part of Western Washington; Bellingham into Vancouver, Canada on Sunday. But I think most of Sunday, Father’s Day, will be really quite decent," he said.
And temperatures should zoom up to around 70. “So not too bad,” Mass said.
Early next week, an upper-level ridge of high pressure develops over the western United States, locking in the sunnier skies.
Sunny Start To Next Week
"And so we expect warming conditions on Monday, Tuesday, maybe into Wednesday. And we could see temperatures hitting upper 70s, 80 quite easily," Mass said.
But it won’t last long. Models show another upper-level troughs of low pressure coming back mid-week, Mass says, so the weather will go downhill again, bringing back cooler temperatures and clouds typical in a normal Northwest spring.
"It’s not like last year," Mass said.
“Last year we had this ridge over us and high pressure and the weather was warm and dry for virtually the whole period from May 15th onward. That’s not true this year."
For a discussion of how a rain shadow has been keeping Seattle strangely dry lately, 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.
