Mass: Rain Returning On Thanksgiving, Possible Lowland Snow Saturday
Forget any hopes you may have had for skiing over the holiday weekend. But you might see some snow at sea level.
KPLU weather expert Cliff Mass says warm winds and heavy rains are in store for the next couple of days, followed by a cold snap that could bring light snow to the lowlands.
“Everything is going to be happening, from floods, winds and even the potential for lowland snow on Saturday,” said Mass.
Mass says a very strong warm front blew through Tuesday afternoon, sending the mercury into the balmy range as subtropical air flooded the region.
“When that came through the winds shifted, they got strong and the temperatures just zoomed up,” Mass said, making it “amazingly warm, upper 50s in many places and windy.”
Flood Watches In Effect
Mass says the combination of warm rain and wind has been causing snow to melt rapidly in the mountains, adding to the very heavy precipitation and causing rivers all over western Washington to swell to flood stage.
“There’s been 5 to 6 inches in some locations,” Mass said. So the combination of the mountain rain and snowmelt has resulted in the rivers coming up “very, very rapidly.”
Flood watches were in effect for the Snohomish, Stillaguamish, Snoqualmie, Cowlitz, Nooksack and Puyallup rivers.
At the same time, in many areas, the mountains were serving as a shield from the heavy precipitation, something Mass calls "profound rain shadowing."
It's a phenomenon normally associated with places on the Olympic Peninsula like Sequim, but Mass says it has also caused very patchy rain effects throughout Puget Sound. He says when the winds come from the west, the effect can be quite pronounced for lowland areas from Olympia to Everett, even while windward parts at the crests of the mountains are getting as much as a half a foot of rain.
Mass says the worst of the flooding is likely over and Wednesday would be “a relatively decent day” as the warm front has shifted north into British Columbia and most of the precipitation moved with it.
“Breezy, but not much precipitation,” Mass said, “But that’s going to change later on.”
Wednesday evening, a “fairly strong” cold front will come in, bringing increased wind, “especially on the coast and around the San Juans. And the precipitation will start this evening and continue into the night,” Mass said.
On Thanksgiving, there will be showers in the morning. And later in the day, Mass says yet another cold front will push through, causing the rain to pick up again Thursday evening.
“So there may be a break in the middle of the day that will allow people to take a little walk around on Thanksgiving, that’s always a good idea,” Mass said. “Nothing severe during Thanksgiving itself.”
But he says the rain from Wednesday and Thursday could total as much as 3 to 5 inches in the mountains.
Cold Snap Friday With Lowland Snow Possible Saturday
Friday will be a transition day to substantially cooler air, which could become cold enough for snow on Saturday, Mass says.
“The latest model runs suggest there is some potential for some light lowland snow in some locations,” he said. “We’re talking about snow down to near sea level during the day on Saturday, so people need to be thinking about that,” though he said it probably won’t stick to most roads.
Sunny conditions will come back on Sunday, but Mass says highs will remain “only in the upper 30s on Saturday and Sunday — you know, this is going to be chilly stuff.”
He says the weekend cold snap could add some inches of snow back into the mountains. “But it will be too late, we had some snow and most of it is melting off right now. So there’s no skiing this weekend, that’s for sure.”
Note: This is a special holiday edition of The Weather with Cliff Mass. We're taking Black Friday off, but will be back at our normal time next week.
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.