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Season's coldest temps ahead. But don't jump to conclusions on cold waves, Mass says.

Ted S. Warren
The Associated Press
A walk signal is illuminated next to snow-coated tree branches, Monday, Feb. 6, 2017, in Seattle.

It’s a tricky forecast, as are most that involve lowland snow around Puget Sound, says KNKX weather expert Cliff Mass.

But residents of Western Washington should brace themselves for the coldest temperatures they’ve seen so far this winter, with a serious possibility of the white stuff hitting near sea level in several areas on Sunday and Monday.

“Today is going to be warm — about 50 degrees — and wet, as a Pacific system moves in, no doubt about that,” Mass said Friday morning.

And he said Saturday will be showery in the morning and pretty warm, with temperatures reaching the mid- to upper 40s, calling it “a decent day.”

This will produce snow in the mountains; Mass says 6-12 inches on Friday alone.

But on Sunday, the weather starts to change. Mass says an upper level trough of low pressure moves southward and begins drawing in cold air from the interior of British Columbia and the Arctic and funneling it to lower elevations.


“So Sunday we’re going to have a cool down — highs only probably in the lower 40s,” Mass said. “So there’s going to be a big transition going on.”

By later in the day on Sunday, Mass says the atmosphere above Western Washington will be cold enough for snow.

He says the cold will start with icy winds pushing through the Fraser River gap, near Bellingham, sometime around mid-to-late day on Sunday.

“And that cold air will push south over Western Washington, Sunday night into Monday,” Mass said. “So by the time we get to Monday, we will have what we call ‘modified Arctic air’ over the Northwest.”  

That means temperatures will only reach a high in the mid-30s and the overnight low will probably drop into the mid-20s.

“So this is going to be the coldest air that’s been over us since last February — and it’s clearly going to be the coldest period of the whole winter.”

Mass says Tuesday should be sunny and cold and he expects the cold to remain for most of the week with perhaps a temporary warm-up, but another chance of lowland snow on Thursday and Friday.


Predicting snow is the tricky part of the forecast, Mass said.

“Where we’ll get snow in the lowlands is extremely difficult,” he said. “I think the most probable area is somewhere between Bellingham and Everett. The cold air comes out of the Fraser River Valley, it’s going to hit some air coming from the south over Puget Sound — there could be a band of snow setting up there.”

He also says when the strong northeasterly flow that’s expected hits the northern part of the Olympics, that could produce snow from Port Townsend all the way to Port Angeles.  But he is not sure about snow showers over the greater Puget Sound region and Seattle.

“I think it is possible there could be scattered snow showers over central Puget Sound on Monday, but there’s definitely nothing really heavy that’s in the forecast,” Mass said. “There is greater chance of snow to the south of us — from Olympia down to Portland, particularly on Monday.”

Mass says even though the snow forecast is iffy, there’s no doubt it will be cold. So it’s a good idea to wrap pipes and faucets and detach hoses before Sunday afternoon. And don’t leave any pets outside.

“It’s definitely going to get down in the mid- to lower 20s, so this is colder air than we’re used to,  so you have got to prepare,” he said.


Mass has been bothered this week by reports in various media (and even reputable sources such as The New York Times) that the big cold snap in the Midwest is part of a bigger trend of cold waves increasing due to climate change, as a kind of side effect of global warming.

“This drives me wild,” Mass said. “That is absolutely not true — in fact, it’s just the opposite.”

Mass says if you check data on official government sites, such as the EPA or NOAA, you can find documentation of the number of cold waves and see that they are dropping.

“Global warming will not increase the number of cold waves. It will decrease the number of cold waves — and that’s exactly what we’ve seen.”

He says this is particularly true in the western states, where there have been far fewer cold waves in recent decades than back in the 1950s and '60s.

“And part of that must be the fact that global warming is preferentially warming the Arctic areas and so the source region of cold air is warming.” Mass said.

To hear the full conversation, 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