Wednesday, November 1, 2017

Snow Expected over Western Washington

The first real blast of cold air will reach western Washington with substantial snow in the mountains, where the snow level will descend to approximately 1000 ft.   There could even be some snow reaching sea level in some very favored locations, such as Bellingham and Port Angeles, downstream of the Fraser River Gap in the Cascades.

In any case, this will be the coldest air over the region since last January, so be prepared.

During the past week, high pressure has dominated our region, producing warmer than normal conditions and lots of sun.    But everything is changing now.  By Thursday morning (5 AM, see below) the upper level ridge (high pressure) area will move westward towards the Aleutians, while a potent trough of low pressure is moving towards the Northwest.  If this was one month later, there would be a serious threat of snow over Seattle.  Real serious.

The forecast of sea level pressure (solid lines) and low-level temperatures (colors) shows very cold air (blue) over British Columbia and a low pressure center (associated with upper trough) over southern Vancouver Island.  An intense pressure difference (or gradient) is found north of the border.  This is when the JAWS music starts.


One day later (Friday, 5 AM), the low has moved to the mouth of the Columbia River and cold air starts pushing into northern Washington State.  With the large pressure difference along the border,  strong and cold northeasterly flow will be moving through the  Fraser River Valley into Bellingham and over the San Juan Islands.
With cold air moving in aloft and upward motion/precipitation from the upper level trough, the Pacific Northwest will not only be wet, but snow will fall in the mountains and in areas cooled by the Fraser River outflow.

Next, let me show you the 24h snowfall maps during the next few days.  For the 24h ending 5 PM Thursday, significant snow will fall in the Cascades, with some locations getting a foot.  Lots over NE Washington.

 The next 24h, with cold air coming through the Fraser River Valley,  shows light snow over some parts of NW Washington and heavier snow over the northern side of the Olympics (down to sea level) as northeasterly flow from the Fraser outflow winds ascends that mountain range.


The 72 hr total snow over the region is impressive, with higher elevations getting 1-2 feet.  Snow in eastern Oregon as well.  Skiers should be excited...we will get a good start on base for this winter.    Snow shoeing will be viable by the weekend.


And yes, don't forget the winds.  Expect strong (30-50 mph) northeasterly wind gusts from Bellingham, across the San Juans to the Olympics (see map for 8 PM Thursday).
The pattern this week is a classic one for a La Nina winter....it will be interesting to see if this configuration is repeated soon.

20 comments:

Kenna Wickman said...

Be careful what you say Cliff or the media outlets will start calling this weather THE STORM OF THE CENTURY!!!!

John K. said...

Or even worse, they will think up a not clever, touchy-feely name for it. One wonders.. when will they get past the need to do that?

Michael DeMarco said...

Some talk about the weather and some talk about the talk about weather.

John Marshall said...

I am so looking forward to this storm, especially given we're likely to have a Fraser River outflow pushing up the north side of the Olympics to give us upslope snow. I'm on top of a 1000' hill facing the Strait, so I'm expecting to wake up Friday morning to snow. Unfortunately, the ground is very warm so it won't freeze or last.

Luck of the draw, I have to be in Seattle by 8:30am Friday morning, so I get drive down a snowy hill at O-Dark-5am or so and through all this neat weather. My wife dreads driving in snow, but I love it. The more challenging the better. And heck, it's all downhill -- how hard can that be?

Eric Blair said...

Portland finally bowed to reality and will start using salt if there's any chance of a repeat from last winter. Now the following question is do they have enough spreaders and the personnel on hand that know how to apply it? I'm being totally serious, the public works people here are totally clueless about snow, ice and just about anything related to wintry weather. It boggles the mind.

Unknown said...

This seems to be starting off in tempo where it stopped. Ice damming and flooding a three story commercial building still fresh in my memory from early 2017. Howling northeasterner out there with a touch of snow whatcom county.

cornbread said...

Snowing in south Bellingham, grass is white.

Kevin said...

Snowing pretty hard on the south side of Bellingham at 10:30 pm. Sticking on the road outside our house. Second of November!

cgt said...

We have a hair over an inch of white at 11:30pm in Bellingham.

John Marshall said...

A little after midnight (Fri am) and some snow fell on top of Bell Hill in Sequim, exactly as forecast. Temps around 31 with "Feels like" at 23. But thanks to the recent warmth, not much is sticking to the still warm pavement. But the grass and bushes look beautifully white. A nice trailer for the coming winter, or so I hope.

My Labs, who got soaked in the cold rain, were not much enthused about the snow. But it is the middle of the night.

It started off as rain, got heavy, then shifted to hail (lots of small stuff), then back to rain and finally to snow as the temps fell. But now at nearly 1am, the moisture looks like its leaving and snow is tapering off.

What's neat is the forecast put all this together at least two days ago. Getting a snow forecast correct in early November is pretty impressive. Nice work.

thezzyzx said...

I drove from NE Seattle to Mercer Island this morning and snow was sticking to cars on Lake City Way and it was nearly white out conditions on I-5 through the U District.

Unknown said...

What do you know about that? It's full on snowing at El. 200 in North Seattle...

brad_tgl said...

10 inches here at 800 ft. elevation here in Port Angeles. Fraser air arrived!

Chris Shotwell said...

Surprised to wake up to snow in Cherry Hill! Some accumulation on cars and grass, but nothing on the pavement.

Mike near Seattle said...

It snowed on Education Hill in Redmond - everything is white except the pavement. Only half an inch or so, though. Our elevation is about 280 feet.

John Bower said...

6 inches of snow overnight in Bellingham. Oh my!

David B. said...

I'm at 100 feet elevation on Bainbridge Island and my lawn is dusted with white this morning!

Tommy Matala said...

Snowing in Burien, Cliff. Where did meteorologists sci nice go wrong this time!

The Gadfly said...

Redmond. Been snowing all day. Wasn't sticking, but now have about a half inch on the ground.

Terry McDonald said...

Just got a dusting up in Revelstoke. The jet stream was too far north for weeks, then pushed south instantly where it looks like it will stay for weeks. It feels more like January in Revelstoke without the snow.