New Year’s Snow Review

As expected, the weak low that passed through from the NNW through Southwestern Washington last night brought scattered snow showers to parts of the area, with the highest amounts being in the Central Sound area between Seattle and Tacoma where a weak but very persistent convergence zone formed. There was an incredible gradient in snow accumulations here… my parents in Madrona reported nothing while there were some reports of half a FOOT in Burien! Take a look at an animated GIF of the Camano Island radar from 9:16 pm last night to 6:55 this morning and watch how the zone develops.

Showers started popping up along a small-scale front extending into the Strait of Juan de Fuca, and these showers slowly moved south as night went on before reforming as a convergence zone and stalling around the South Seattle area in the early morning hours of Sunday. There, the convergence zone strengthened and even formed a “double” convergence zone at one point with the appearance of an arrowhead!

Here are some snow totals I received from viewers via WeatherTogether’s Facebook page!

Washington:

Burien: 6 inches
North Bend, 3 inches, 610 feet
Sedro-Wooley, 100 feet: 3 inches
Sea-Tac: 3 inches
West Seattle: 2 inches
Snoqualmie: 472 feet: 1 inch on “roads, roofs, and elk”
Little Bear Creek, 260 feet: .5-.75 inches
Sequim: .5 inches
North Beacon Hill, 320 feet: .5 inches (
Capitol Hill: <.5 inches and foggy
Woodinville atop Hollywood hill, 200 feet: dusting
Central Distal District: Trace
U District: Trace
Keyport, 10 feet: nothing
Forest Park (near Everett, WA): nothing

Oregon:

Klamath Falls, 4,320 feet: .5 inches
Scappoose 62 feet: less than .5 inches with a thin and short-lived coating of ice on top
Salem: Trace

Idaho:

Sandpoint, 4,300 feet: 10 inches, 12 degrees

Texas:

0 inches.

For a more complete list of snow totals compiled by the National Weather Service, check out this link.

Snow amounts were highly variable, with some people getting dumped on and others getting very little. This type of scenario where a convergence zone stalls across a small area and delivers a large amount of snow has happened several times over the past couple years… November 27, 2006 (Seahawks/Packers Monday night football game), December 18, 2008 (which caused this reaction from my friends), February 26, 2009, and January 15, 2012 (which gave downtown Seattle 3 inches) are just a few examples. This zone was a bit weaker than the 2006 or 2008 zones but was pretty darn similar to the 2012 zone, just a little bit further south. Thank you Mattias Keese for helping me with this analysis.

These things are difficult enough to forecast – models are not able to accurately pin down the location and strength of these convergence zones, so we have to make a “broadbrush” forecast highlighting the possibility of scattered snow over a wide area but still mentioning that many people won’t see much. The REAL difficulty is effectively communicating that most some places will see nothing and others could see several inches.  The “several inches” sticks in people’s minds more, and for good reason!

We’ve been drying out today as the low pressure system that gave us this moisture and convergence continues to move southward. Cold, arctic air has been surging into the region, though it is not as cold as previously feared.

This feature looked fascinating on this afternoon’s shot from NASA’s MODIS imager. You can see extremely cold air to our north coming over the Pacific and picking up moisture as it does so. This is the same sort of phenomenon that gives “lake effect” snow to areas downwind of the Great Lakes when arctic air blasts through there in the winter.

We are still very cold for Monday through Wednesday, with sunny skies and highs struggling to reach freezing. Lows will be around 20 in the city to the teens in outlying locations. Because they saw several inches of snow, Sea-Tac will likely dip into the teens, as fresh snow cover helps radiate heat more effectively to the atmosphere at night.

The extended forecast has changed significantly from the last time we talked, with some models now advertising a far warmer scenario rather than another arctic blast and snow. However, the models have been UNBELIEVABLY inconsistent. This afternoon’s forecast discussion from the Medford National Weather Service offered a far more eloquent discussion of the maladies of the models than I ever could, stating that the forecaster couldn’t “recall seeing quite so large a model difference in temperatures for our area in my entire career.”

I’ll have an extended post on all of this tomorrow. There’s a lot to talk about, and the model disagreement and their reasons for disagreeing are very fascinating. Long story short, they differ in whether the trough that has dug over us and given us arctic outflow will become absorbed with a cut-off low near 150 W associated with a giant Rex Block in the Eastern Pacific. If that sounds complicated, it is!

Have a nice night!
Charlie