The Lowland Snow Outlook, A Wind Surge through the Strait, Amazing Precipitation Totals, and Problematic Passes

A huge amount of weather has occurred and we are now within the high-resolution forecast period for the lowland snow event on Monday.

The atmospheric river of Thursday/Friday did not disappoint, with some locations securing nearly 10 inches of precipitation (see 48-h totals below).  Several local rivers reached flood stage and major regional reservoirs have begun to fill.  

It is probably time for the US Drought Monitor to drop the SEVERE drought over western Washington 

😊

The warm/moist atmospheric river situation was ended late Friday by the arrival of a powerful cold front moving in from the Northwest.     

Behind the front, a very strong westerly wind surge pushed down the Strait of Juan de Fuca, with winds reaching 60-70 mph, resulting in tens of thousands of customers losing power in the north Sound area.   Our WRF modeling system provided an excellent forecast of the wind event (see below, blue and light blue are the strongest winds)).

Behind the front was cool, unstable air that, forced to rise by the mountains, produced lots of snow in the mountains, closing some passes for a while and causing chains to be required (see below).

OK...there has been lots of intense, interesting weather the past few days, but what many really want to know about is whether there will be lowland snow.

And the answer is yes...but it will only be in certain locations.  Interestingly, the problem won't be cold--it will be precipitation!

On Monday, a powerful current of cold, northwesterly winds will push out of the Fraser River Valley across Bellingham and the San Juans, then push into the Olympics and out the Strait of Juan de Fuca (see below, blue colors indicate temperatures cold enough to snow).

And by Tuesday morning, some of that cold air will push into Puget Sound (see below)

Now let's look at the accumulated snowfall through Tuesday morning from the UW high-resolution model (see below).   Huge amounts in the mountains (feet).  Several inches from Bellingham to the San Juans.  Snow at low levels along the Strait of Juan De Fuca and east or south of the Olympics....and even a few flakes over north Seattle.  

An important factor working against the snow is easterly downslope flow on the western side of the central Cascades and the general lack of general precipitation because the strongest atmospheric forcing will be south of us.    Will watch the evolution closely.

PS:  On Friday I did not bike to work because I feared falling trees from the winds.  Driving along San Point Way, I saw a huge branch fall around 5:45PM, hitting a powerline, causing a fountain of sparks, and then knocking out the power.   Including my home.  You really have to respect and appreciate the linemen/linewomen that go up into the lines to restore power.