Friday, February 16, 2018

Cold and Snow

We are about to enter the coldest period in over a year (since December 2016 at least), with massive snow in the mountains and lowland snow in "favored" areas such as Northwest Washington and the northern slopes of the Olympics.  Even Seattle might get a dusting. I expect to break some daily low temperature records before it is over.

And if you don't want to support your local plumber, disconnect your outdoor hoses and protect exposed pipes.   And make sure your pets are warm.   Seattle will have to deal with its large homeless population, many of whom will be exposed to below-freezing temperatures for several days.

Let's start by looking at the 72hr snowfall forecast from 4 PM last night until 4 PM Sunday by the highest resolution model we run at the UW.  Two to three feet in the Cascade at the higher elevations of the Olympics.  With a low freezing/snow level, Snoqualmie Pass will get bountiful snow.  Just good news for skiers.  This snowfall will guarantee the rest of the season.


And here is a close up view of snowfall for the same period.  Note the snow around Port Angeles to Port Townsend!   This is due to upslope flow as air from the Fraser River valley jets out to the SW over Northwest Washington.

To illustrate this flow, here are the winds at 4 AM Sunday, showing winds from the Fraser Gap accelerating over the water and then heading toward the Olympics, with some of the cool air peeling southward towards Puget Sound.


You will notice the Puget Sound does not get a lot of snow.  The reason?  We are going to be heavily rainshadowed (snow shadowed) by the Olympics since the general flow is westerly/northwesterly.  But we do have a chance of a snowburst as the leading edge of the cold air from the Fraser (known as the "arctic front" in the business) moves through.  No more than an inch, though.

And then there is the cold air, which moves in Sunday and stays for several days.  Sunday night/Monday morning will bring temperatures dropping into the 20s in western WA and below zero to the higher terrain and eastern WA.   Here is the UW WRF model forecast for 4 AM Monday.  Twenties near Puget Sound and the water, dropping to the upper teens in the Cascade foothills and single digits and below over the Cascades and northeast Washington.   And it will be even cooler Tuesday morning.


The surface air temperature prediction for Tuesday morning is amazing cold, with temperatures below -8F pushing over much of the interior Northwest.   Even northern coastal California will get below freezing!


Stay warming...and be ready for unusually cold temperatures.

9 comments:

Harrison said...

We got 10” last night at Crystal on top of the 9” earlier in the week, and will see 16” more Saturday and Saturday night. Come on up and say hi! Us Lifty’s would love to see you.

Lucas Flanders said...

It will be interesting to see what the Frazer River outflow winds do over the eastern San Juan archipelago during this event. They are almost always stronger locally than forecast.

John McBride said...

My mother's mother was born in 1892 and told of a snowstorm in February in Seattle in 1916 that crushed barns, buried roads and brought down the once-upon-a-time dome that crowned St. James Cathedral on First Hill.

John said...

Snow/cold lovers should just love the latest 6-10 and 8-14 day temp and precip maps that just came out from the CPC!

Udayan said...

Not much snow expected in Seattle, luckily!

Terry McDonald said...

Things are getting excessive in Revelstoke. 4-5 feet now in my backyard at the town elevation of 500m. Had to shovel my carport roof twice so far and it doesn't look like it will be going anywhere for awhile with cold temperatures until at least March and more snow in the forecast. Funny thing is we had no snow on the ground until the week leading into Christmas this year with abysmal coverage on the mountain below 1800m...

http://www.revelstokemountainresort.com/conditions/historical-snowfall

Looking at snow pack surveys I'm curious why we've had such a narrow band of snow and favorable temperatures this year thus far? getting into southern washington the snowpack drops dramatically with which has been dominated by mild + dry weather or mild + wet weather... while the northern part of BC has been dominated by cold + dry weather with well below average snowpack.




Ron Sorrell said...

Which chair you running? I will say hi fo sho! Also, you think southback and northway will be openoon Sunday?

Hal said...

That storm was on 2 Feb 1916. Historylink has a page about it: http://historylink.org/File/2872

Thecatguy93 said...

I'm in Wenatchee for the weekend and it is dumping snow here this morning. This wasn't in the forecast until overnight tonight and tomorrow.