Some skating on thin ice; others skating by for now

Some skating on thin ice; others skating by for now
SEATTLE -- In a stark reminder of how much the weather can vary over a short distance in the Pacific Northwest, some areas just north of the Everett metro area were buried under 4-12" inches of snow Wednesday.

Meanwhile, 60 miles to the south, nary a snowflake to be found.

That was the case just 30 miles to the south too until a vigorous Convergence Zone formed in Southern Snohomish and northern King County, bringing a heavy snow between Everett and Shoreline in the heart of the evening commute. Traffic instantly slowed to a crawl on I-5 and I-405 in the north end as snow began to stick to the roadways. Side streets throughout Bothell were said to be filled with spinouts.

Several buses were seen stuck on icy roadways across the Puget Sound area during the commute. The buses were trapped on the slick pavements, helpless and immobile until an oversized tow truck came by and gave them a push.

The Zone stubbornly was hanging in Snohomish County, continuing to bring snow to the greater Everett/Snohomish County and Skagit County areas Wednesday evening, where as much as two feet of snow had fallen earlier in the day. Eventually, it will drift south overnight in the pre-dawn hours Thursday, perhaps bringing a few inches of snow to King County, possibly as late as the Thursday morning commute.

Convergence Zones are very fickle and have a mind of their own, but the north wind will eventually win out and push the zone south...sometime. In the meantime, it is bringing a relentless snow to the western Skagit and Snohomish County regions.

A WINTER STORM WARNING remains in effect until 10 a.m. Thursday for the north interior from Everett north to the Canadian border, and west along the Olympic Peninsula over to the North Coast. This includes all the northern islands. Also included in the warning are the foothills of King and Snohomish County, including Bellevue, Issaquah, North Bend and Bonney Lake.

Here are the specific snow forecasts listed for those in the warning:

For the North Interior (Skagit/Whatcom/San Juan Counties), you could receive 1-3" of additional snow from late evening through the night, with as much as 6" new in western Skagit County, adding to the 8-23" already there. Greater Everett/South Snohomish County areas could see 1-4" this evening and overnight, with perhaps trending 4-7" of more snow in northern Snohomish County. It will also be quite windy in the greater Bellingham area with gusts to 40-50 mph.

Along the north Olympic Peninsula, 1-4" is possible by Thursday morning as showers roll down the Strait of Juan de Fuca, with the higher end of those totals in the Olympic foothills.

The King and Snohomish County foothills, including the higher spots of Bellevue, Issaquah, North Bend and Bonney Lake could see 1-3" as the night progresses whenever the zone decides to move south, with the higher amounts in the higher elevations.

The North Coast could see 1-3" of snow in scattered showers.

A WINTER WEATHER ADVISORY remains in effect for the Seattle-Tacoma metro area, Kitsap Peninsula, and southwestern interior. Here, 1-3" is possible, with the 3" trending more toward North Seattle (maybe 4" here) and the hilltops, and 1-2" in the Seattle/Tacoma lowlands. This snow may not reach here until near daybreak Thursday.

Snow showers will also bring spotty accumulations of 1-3" in the southwestern Interior, including Olympia, and the Hood Canal area, but otherwise mainly east of I-5

Whatever falls might freeze

As the night progresses, colder air will continue to filter in from the north, dropping overnight lows to around freezing. It doesn't look like we'll get the super hard freeze as the cold, north winds have been delayed until the pre-dawn hours Thursday.

What's Up With This Convergence Zone?

Convergence Zones are caused by colliding winds -- a north wind from the north and a south wind from the south. When those winds collide, they get forced upward, where the air condenses into clouds and storms form. Zones historically are responsible for some of the area's greatest snows, and this one was no different. Arlington had a snow report of 23" as of 10 p.m. Wednesday, and all that snow that fell into Skagit and Snohomish County from about noon on has been at the hand of these colliding winds.

The massive snow storm of Dec. 18, 1990 was also born from a Convergence Zone that set up shop over Downtown Seattle. So far, this one has had a stronger southerly component, keeping the zone up north. Computer forecasting models correctly predicted this zone's formation, but so far, underestimated the storm's southerly wind component, keeping the zone north of the city.

But imagine taking the 5-10" of snow that has fallen in some spots in the Zone this evening and will continue to fall overnight, and shift that just 30 miles south, and you were talking potentially several inches of snow in the heart of Seattle during the day. That was why there were such dire warnings, and why schools were closed. Zones form quickly and can shift very quickly, and there would not have been much time to react. Just look at all the poor people stuck in the monster traffic jams this evening around the King/Snohomish County line who were caught in this snow.

The zone, as of 10 p.m., was up near the Skagit County line, but was still expected to push south at some point overnight or near sunrise Thursday. When or how strong will it be when it does so? Hard to say. But even though it is way late, there is still a chance of snow when this line passes through.

Earlier Today:

Reports of 4-10" of new snow had already fallen across Skagit, Island and northern Snohomish County by early afternoon. The DOT reported whiteout conditions in the Mount Vernon/Skagit County area for a time Wednesday morning.

Some South Sound areas also got hit hard. We've received a report of 6" of snow in Olympia as well with several roads closed throughout the city. Snow has also brought up to an inch or so to the Gig Harbor area as well as Puyallup's South Hill.

The snow prompted several school closures and delays. Get the latest information at this link.

Here are some snow totals reported so far:

  • Arlington (Outskirts): 23"
  • Darrington: 14"
  • Randle: 13.5"
  • Mount Vernon: 8"
  • Stanwood: 8"
  • Anacortes: 6.5"
  • Hamilton: 6.2"
  • Olympia: 6"
  • Marysville: 6"
  • Granite Falls: 5.5"
  • Oak Harbor: 5"
  • Bellingham: 5"
  • Port Townsend: 4"
  • Arlington: 4"
  • Mill Creek: 3.1"
  • South Everett: 3"
  • Hoodsport: 3"
  • Bothell: 2"
  • Grand Mound: 1.5"
  • Woodinville: 1"
  • Mountlake Terrace: 1"

What Was Up With The Seattle Snow? (Or Lack Thereof?)

If you heard me on the Commentators this morning, "the mountains stole it". We had strong westerly flow aloft rotating around a low pressure system situated off the north coast.

But that west wind smashed into the western slopes of the Olympic Mountains, then dried out as it sank down the eastern slopes on the other side. This is typically what protects Sequim from rain and why they are the driest city in the region. But usually, winds are southwest to northeast during a regular storm. This one was different.

That created a cone of dry air right over the greater Seattle/Central King County area, and it held strong through the day.

Meanwhile, at the surface, while the low was parked to our north, the low level wind veered from the south and brought in some warmer, mild air through the Puget Sound region, warming us up into the upper 30s, keeping what few showers managed to sneak into the area as rain.

Outside the shadow, snow fell heavily to the north and south of the Olympics as that moisture from the low ran into the cold air in place.

Where Do We Go From Here?

We could see some lingering snow showers Thursday into early Thursday morning, putting down an additional 1" or so in spots, but generally mostly cloudy early and clearing late. Highs will only top out around the freezing mark.

Thursday night will be clearing and cold, with lows in 15-21 range.

Friday should be a lot like earlier this week -- sunny but continued cold -- possibly a few degrees colder than this current spell -- with highs 25-28 and lows Friday night from 10-18.

Saturday also looks dry and continued cold with highs in the mid 20s. But clouds will increase Saturday night, keeping lows around 20.

Those clouds are a signal of our next great forecasting challenge -- a storm heading in for Sunday. This one presents a whole new set of variables, because Mother Nature has a devious sense of humor and a thick playbook, it seems.

This storm is coming in from the west/northwest, and it looks pretty wet. Second, we'll not only have some arctic air here in Western Washington, but even more in Eastern Washington. That air is very dense, and thus has higher pressure.

As the low pressure of the storm approaches, forecasting models are hinting now that we could see some very strong, gusty east winds in the passes to the usual North Bend, Enumclaw, Gold Bar east-windy places -- perhaps as high as 40-50 mph.

That's challenge A. Challenge B -- if so, that would be blowing in a lot of cold air from Eastern Washington into Western Washington -- the "North Bend gets to feel like Bellingham does now for a while" scenario, getting even more cold air into the region ahead of this storm.

So when the storm arrives, in the areas outside the wind, depending on how warm the storm is and how much cold air is around, it'll likely start as heavy snow, then gradually change to rain.

But in areas where that east wind keeps feeding the cold air in, this could present some freezing rain problems along the I-90 corridor. (Portland people can tell us all about this, since they have frequent experience with a similar set up with the east wind blowing out from the Columbia Gorge. In fact, this set up presents them with similar freezing rain problems for their area.)

Bottom line: Sunday could be real messy. It might be lucky for us if the system comes in cooler and it stays as snow because while it'd be quite a bit of snow, ice/freezing rain would be worse. (About all that's left is the blizzard and we'd have collected the entire set of weather problems :) ) Highs will be somewhere between 31-38.

It looks like we dry out for Monday and Tuesday with partly to mostly sunny skies and highs in the low-mid 30s and lows still in the 20s.

Another not-so-frigid system moves through on Christmas Eve, but at this point, this is looking like the kicker of just snow to rain and highs into the 40s, perhaps ending the cold spell. But a more southerly track, and we could get that White Christmas after all :)

More Information

Here are several links to more information and tidbits about the storm from Scott's weather blog: