A Major Snowstorm Will Hit the Region Starting Late Friday

The weather forecast models are now pretty much on the same page for the next snow event and confidence in the forecast is quite high:   there is going to be a major snow event over much of the Pacific Northwest starting late Friday and continuing into the weekend.

A much larger snow event than occurred on Sunday night/Monday morning of this week.  And one in which snow will be falling on a surface that is now cooled substantially.

I have studied Northwest snowstorms for years and even co-authored a paper on the subject.  What is forecast to occur late Friday and this weekend is absolutely classic.

I will start by showing you the latest forecast of the UW high-resolution weather modeling system.   The 24-h accumulation ending 4 PM Friday shows the snow moving into the northern portion of Washington, with heavy snow already falling in southern BC (see below).  In the Puget Sound region you MAY be able to get home before the real action hits.

The snowfall over the next 24hr is extraordinary, with up to 8 inches over Puget Sound and over a foot on the northern side of the Olympics.

The set-up for this snow event is nearly perfect, with a low center near the SW tip of WA State and very cold air over British Columbia.  The reason why this is the "perfect" snowstorm situation is that the low center draws cold air into western WA from BC (a lot of it through the Fraser River Valley), while pushing moist air overhead.  A veritable snow machine.

The UW model is driven by the U.S. GFS model on its boundaries.  The ensemble forecasts of Seattle snow from many GFS runs is shown below.   All the runs are going for snow, with an average of around 3.5 inches.   Most the ensemble members are relatively low resolution.  The higher resolution member of the ensemble (blue line) is going for about 7.5 inches.

What does the highly respected European Center Model predict?  For the 24-h ending 4 AM Friday, very little over WA State.

But by 4 AM Saturday, most of western WA is snowbound with around 4 inches over Seattle and more to the east.

 The snow continues into Sunday morning, particularly over Oregon.  Roughly a half-foot over Seattle

But I fear to tell you what the EC model predicts next.  There is a second snow event on Monday/early Tuesday that doubles the snowfall in some locations.   The accumulated snow through the weekend ending 4 AM Tuesday is shown below.  We are talking over a foot of snow in central Puget Sound.  Two feet in some of the foothills locations. Unbelievable.

 And even more by Wednesday morning (see below). Snow apocalypse.  One of greatest snow events in decades.   And yes, there is a lot of uncertainty for the second event.

How confident are we in the ECMWF forecast?  Well, lets check their large (51 member ensemble of forecasts, each slightly different) for accumulated snowfall at Sea Tac--see below, top panel. Nearly all of the forecasts are going for 4-6 inches before Saturday is over...some more. But what about the second storm? Roughly 2/3rds of the forecasts are going for a large event (reddish colors-means around a foot of snow). The bottom panel shows the ensemble mean..ends up around 8 inches and their high resolution (deterministic) run...ending up with around twenty inches by the the middle of next week. Yes, we could end up with one of the forecast busts...but every run gets something significant.

The bottom line:  the late Friday/early Saturday event will bring major snowfall to the lowlands, with more accumulation than the last event.  Confidence is high based on both NOAA/NWS and European Center ensembles.   Both modeling systems are suggesting a second event starting on Monday, with the European Center going for a huge snow dump.  Confidence is less because there are differences in the model solutions for that period.  

SDOT, WSDOT, and other local department's of transportation need to get prepared for perhaps the snowiest period since the large snowfall of December 1996, when Seattle received 21 inches.  And yes, you might stock up on food before noon on Friday.  I certainly am.