Snow Flurries, Real Snow, Then a Meltdown

 Update Thursday AM:  The model solutions have evolved....snow over WA is going to be delayed or avoided...I go blog about it later today.  Enjoy the sun and cold....cliff


Some folks west of the Cascade crest are going to receive several inches of snow as a warm front approaches....but exactly who that will be is still not clear.

Cold air has spread over Washington and most of Oregon--more than cold enough to snow if moisture dared to show its face.  In fact, a weak upper disturbance brought some flurries to the area today, but no accumulation.

Here is the forecast sea level pressures, surface winds, and lower atmosphere temperatures this evening at 10 PM.

The truly cold air is east of the Rockies, which affords us some protection.  Intermediate cold air has reaches eastern Washington, and western Washington, protected by the Cascades, has milder (but still cold air) over us.  Temperatures remained below 35F for most of the western lowlands today.  There is a good pressure difference across the Cascades, resulting in winds accelerating down the Fraser River gap.  Take a look at the max surface winds during the past 24 h over NW corner of WA:

Several locations got to 40-50 mph.   The constrained nature of this "jet" of cool, dry air from the interior is obvious.  Drive 20 miles north or south of core of the strong winds and you are out of them.
       The big weather story will wait until Saturday.  We have cool air over us, and a strong warm front with substantial moisture will be approaching. Here is the predicted surface map for 4 AM on Saturday. Cold air still over Washington and northern Oregon, but you see the yellow colors (warm air) offshore.  And if you look closely you will see a wind shift from SW to NE winds and a big change in color in the same area.  That is an approaching warm front.

Such fronts cause uplift and precipitation.  Here is the three-hour precipitation ending the same time--you see what I mean.

As the front approaches, the cold air will hold for several hours, resulting in  inches of snow and perhaps a half-foot in some lucky locations.  But eventually, the warm front will push through, producing a melting slushy mess for a few hours.

Here is the 24h snowfall for the 24h ending 4 AM on Sunday and 4 AM on Monday.  In this solution, the heaviest snow hits Oregon, with the Cascades in both states getting a half-foot.  But the snow solutions have not been stable from run to run, so we need to wait to be sure.

We are lucky that this snow event is now occurring on a weekend.   And Seattle is far more prepared for snow than cities such as Atlanta, where local officials did not properly prepare their city, even with a decent forecast. 

Seahawks, Groundhogs, and Cold

First, lets consider the most important issue first: Punxsutawney Phil saw his shadow today, which means 6 more weeks of winter.   This result is consistent with seasonal climate models, such as the NOAA Climate Forecast System Model, which suggest that there will be some persistence to dry/warm/west with cold east pattern we have seen.  The idea of his seeing his shadow implying cool temperatures makes some sense, since that would imply high pressure and cold air is over the East Coast.

Seattle is on pins and needles about the Seahawks game, and for good reason.  The forecast situation is consistent with what was predicted a few days ago.

Today is relatively mild over East Rutherford, NJ with highs getting up into the higher 40s.  A frontal zone is slowly approaching the Super  Bowl site (see image), where it is now partly cloudy.

As shown by the NWS forecast, which I think is quite reasonable, the game will start (6:30 PM) in the lower to mid-forties (under clouds), with cooling to around 37-38F by the end (top panel has temp-red, wind chill -green, dew point-blue, middle panel has wind, lower panel has prob of precip-brown). Very much Seattle-like conditions that will make the Seahawks feel comfortable. Winds from the north at 5-10 mph.

 The big question is precipitation....this is going to be close.  The latest NOAA Rapid Refresh Model runs (they run the model every hour using all available regional observations) suggest that light precipitation...probably rain..will get there at the very end of the game.  The RAP simulated radar image for 7 PM shows dry conditions over MetLife stadium

7 

Here the predicted radar image for midnight--some light showers have reached the venue.

The threat of rain will surely unnerve the Broncos, considering the arid environment for which they are accustomed.

Finally, the Northwest is about to enter a cold period that will be quite dry in Washington.  The surface chart of Tuesday morning says it all (purples are very cold temps).  Over Washington expect offshore (easterly) flow, which ensures sun and little precipitation.  Our high temperatures will ONLY get into the mid-30s!

A meteorological irony is that Washington's cold and sun  gives Oregon and California a chance for precipitation as the frontal zone moves southward.   Take a look at the precipitation for the next 72 hr and the 72h after that.  First, the precipitation through Wednesday at 4 AM.  Oregon gets wet (snow in the mountains there!) and the northern Rockies do very well.  Even CA getting something...but not much.

The next 72 h is dry for Washington and Oregon, but thankfully California get more significant precipitation.  Those poor devils need every drop

And there is much I haven't talked about....like the strong NE winds that will hit Bellingham and NW Washington!   The wind chills there will be serious.  And don't forget the potential western Washington snowstorm on Saturday!