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.