Snow snarls evening commute; ice threatens morning drive

What's new and now: All snow advisories/warnings expired at 10 p.m. as Convergence Zone weakens. However, snow showers still remain in the area with Trace-1" additional accumulations through about midnight-2 a.m. Snow totals across the South Sound are now up to 4-6". Arctic front reaches Bellingham on its way south through Puget Sound area.

Updated snow totals at the bottom of this story.

Talk about déjà vu.

An intense Puget Sound Convergence Zone formed over the Snohomish County, then quickly slid south into Seattle/Bellevue metro area right in the heart of the evening commute Wednesday, coating roads with snow and ice and bringing traffic to a complete standstill. It was eerily reminiscent of the Nov. 27 snowstorm that brought heavy snow to the North Sound areas during the afternoon, then pushed south through King County during the height of rush hour.

DOT cameras at 5:30 p.m. showed traffic at a dead stop across I-90 and along I-405 on the Eastside. I-5 was a mess as well, but gradually improved. Three hours later, traffic was still at a standstill along eastbound I-90 and I-405 from Bellevue south toward Renton. Most everyone had gotten home by 10 p.m.

The Convergence Zone was gradually weakening Wednesday night, and all snow warnings expired at 10 p.m. At its peak, the Zone was putting out snow at the rate of 1-2" an hour. Issaquah reported 6", while Des Moines said 5" and Renton was at 6". Some snow showers were still around as of 10:30 p.m. but were expected to taper off over the next few hours.

Aside from the 4-6" in the Zone, snow totals from the storm have ranged from 1-2" in the Puget Sound area to 5-12" in Skagit, Whatcom and San Juan Counties.

Arctic air was working its way south overnight. As that front passes is when the temperatures will really drop. We're expecting lows to bottom out near 20-23 by dawn. That means anywhere the roads are wet -- and thanks to that Zone, just about the entire greater Seattle commuting area qualifies -- it will be solid ice Thursday morning. Expect a very dangerous and treacherous commute in the morning and allow a lot of extra time to get where you're going....or perhaps put off travel until later in the day.

North winds will also pick up behind the front and be gusty to about 20-30 mph. That will make for wind chills in the single digits and teens.

Thursday will be sunny, breezy, and very cold. Highs will struggle through the 20s and might eke their way to the low 30s by afternoon. Wind chills again will be in the teens. And don't forget the ice.

An even colder night Thursday night, with lows dropping into the 12-18 degree range, so yet another very icy start Friday. We stay sunny and gradually moderate through the weekend, adding about 3 degrees to our highs and lows each day, getting back into the low 40s by the start of next week.

The Meteorological Mumbo-Jumbo

As we've alluded to, it was quite a complex weather pattern Wednesday (isn't it always, with snow?) I'm sure the meteorological community will be analyzing it for months to come.

It all began Tuesday with that windstorm that brought wind gusts as high as 60-64 mph and knocked out power to about 7,000 people. But while we've seen that about 20 times so far this fall and winter, this time the storm had an impressive pool of cold air behind it.

But where that cold air is coming from is a little unusual. Typically, our really cold air comes from the Canadian interior, funneled in via a north wind through the Fraser Valley. This time, the cold air is, at least initially, coming from the Gulf of Alaska. Normally, that pattern doesn't make for much snow because the air has a long time to moderate over the warmer ocean waters. But the air mass up there is SO cold -- Anchorage was at -12 Tuesday -- that even with the ocean's moderating effects, the air was still cold enough to snow by the time it made it here.

A second area of low pressure moved through the northern half of the state during the midday and early afternoon hours, intensifying as it moved east down the Strait of Juan de Fuca. It brought a heavy snow to Whidbey, Camano and the San Juan Islands before pushing into Skagit and Snohomish Counties, with a quick 1-3" of snow there.

As that low passed over the I-5 corridor, north winds behind the low quickly raced down the Puget Sound area and collided with the persistent south winds already there, making for a quick and energized Puget Sound Convergence Zone.

It's that Zone brought heavy snow and snow pellet showers to central King and southern Snohomish County right around 4:30 -- and the start of the commute. It then slid south and then stalled right over Central and southern King County, reaching over into northern Pierce County through the evening, bringing continuing snow there.

The next piece of the puzzle is the arctic front to sink south and clear out the Zone and usher in the even colder air.

How Much Snow Fell?

Here's some snow totals from the storm:

Fall City: 13"
Ferndale: 11"
Gold Bar: 10.5"
Sultan: 10"
Snoqualmie Ridge: 9"
Orcas Island: 9"
Renton: 7.5"
Bellingham: 7"
Duvall: 7"
Tacoma: 7"
Sequim: 6.5"
Issaquah: 6"
Federal Way: 6"
Maple Valley: 6"
Beacon Hill: 5"
Des Moines: 5"
Anacortes: 4"
Port Angeles: 3"
Belfair: 3"
Kent: 3"
Puyallup: 2"
Raymond: 2"
Mill Creek: 2"
Belfair: 2"
Everett: 2"
Mukilteo: 1.5"
Olympia: 1.5"