Lowland Snow over Western Washington Tonight? American versus European Models

 Update at 10 PM.  Looks like some mixed rain /snow and wet snow in the South Sound away from the water, increasing with elevation.  Some accumulation above 500 ft.

_________________

A very interesting forecast dilemma is before local meteorologists tonight.

On one hand, the U.S. high-resolution model (HRRR) is predicting as much as 8 inches over the South Sound and 5 inches at SeaTac Airport by 11 AM Friday morning. The U.S. GFS model is doing the same.  Most of the snow will fall overnight.

 

In contrast, the European Center model, which is generally the most accurate (remember the missing bomb cyclone in December?), is NOT going for lowland snow.  Zippo.

Keep in mind, this is snowfall, not snow depth.   This is going to be very wet, melting snow in any case, and snow depths will be MUCH, MUCH less.

An interesting aspect of this event is the large north-south temperature change forecast over the region.  Below is the forecast temperatures around 5000 ft  (850 hPa pressure) at 5 AM tomorrow morning.   Huge contrast over southern Washington (blue cold, green warmer).  A small error in position would be significant.

Currently, the freezing level is around 1600 ft at SeaTac (see below), much too high for snow reaching sea level.   The snow level (where all the snow has melted) is about 1000 ft below the freezing level.  But it should decline slowly.

What about uncertainty in the forecasts?  It is HUGE.   The UW high-resolution model, forced by many global models, shows a wide range of possibilities. Many forecasts are for zero, others as much as 4 inches of snowfall (NOT SNOW DEPTH).

I suspect the European Center projections will be closer to the truth.  Near sea level, some of you may see some flakes tomorrow morning in the central and south Sound near sea level (500 ft and below elevation).  But nothing significant.  Snowfall will increase rapidly above 500 ft.

In contrast, the central and south Cascades will be hit hard (see accumulated snow through Sunday morning).  Feet of fresh snow.  The mountains of SE Washington will also get plentiful powder.

Winter is NOT Over: Strong Winds, Heavy Rain, and Substantial Mountain Snow Ahead

Tomorrow and Thursday should bring very active weather to our region, including bountiful precipitation, heavy mountain snow, and gusty winds.

Local ski areas don't mince words.  They are terming this "Miracle March":

But many old weather hands expected this transition, and the models have been hinting at it for a while.

First, the winds.   A modest low-pressure center will make landfall on Vancouver Island, producing a strong north-south pressure difference over western Washington ( see map below)

That means strong southerly winds.  Turning to the Seattle WindWatch system, the forecast maximum wind gusts will accelerate to around 40 mph over Seattle late tomorrow afternoon.  Not the end of the world, but expect a few scattered power outages.

South of the low, a potent atmospheric river will approach the Northwest coast, bringing heavy precipitation.

The forecast accumulated precipitation through Saturday morning is shown below, with up to ten inches (of liquid water) in the southern Cascades.  EXACTLY where it is needed most. Plenty elsewhere.

And temperatures will be sufficiently cold so that the Cascades will get a massive snow dump (total through Friday afternoon shown below).  Yellow and white colors are two feet or more. Ski folds will be happy.

Again, just where it was needed the most.

The National Weather Service has a blizzard warning out for the Cascades and Olympics, plus a wind advisory for most of western Washington.

This winter started as a lion (heavy rain and flooding), turned into a lamb, and reverted back to a lion again.