Drivers prepare for rough commutes

By Scott Sistek Published: Dec 16, 2008 at 5:20 PM PST Last Updated: Dec 17, 2008 at 5:47 AM PST
Drivers prepare for rough commutes »Play Video
Jake in his first snow in Lake Stevens. By YouNews contributor tmh23
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SEATTLE -- Both your commute into, and home from work Wednesday could be a snowy mess if you drive during the regular rush hours, as a one-two punch of snow is expected to blow through the Puget Sound region Wednesday.

A WINTER STORM WARNING is in effect for several areas in Western Washington, where over 4" of snow could accumulate by Wednesday night as a storm drops south from northern British Columbia and combines moisture with our very chilly temperatures. Even in Seattle, the city areas could see a few inches of snow during the day and evening.

It looks like snow will begin around midnight near the Canadian border and spread south through the daybreak hours. Arrival in the Puget Sound now looks like around 6-9 a.m., very likely affecting the Wednesday morning commute. (See at the bottom of this story for this broken down by time line instead of region.)

It appears the general game plan will be for the storm to bring a round of snow from the north as the morning progresses, passing through the Puget Sound area by late morning/midday and then moving into Southwestern Washington. In the storm's wake, a pseudo-Convergence Zone is likely to form, bringing another bout of snow between North Seattle and Everett, and stretching east to the mountains. All other areas will see snow taper off from the north during the afternoon.

There's a small wrinkle here that we could actually see a change over to a mix or rain near sea level in the Seattle-Tacoma area once this first band of snow passes and some milder air sneaks in. But this second wave for the afternoon/evening will crash the snow level back down to sea level, so don't let your guard down if you see some rain in the early afternoon.

How bad will it be? That's the $64 billion question. (What, we can't ask for a federal bailout too? :) ) As usual with snow, there are several factors in play and a change to one facet can make a difference between a dusting and a deluge.

From a forecasting standpoint, we have one salvation this time -- we're confident the air mass will be cold enough at the start of this event to be snow just about everywhere, perhaps save for the immediate ocean beaches. But I'll be bold and stick my neck out and try to give some regional snow forecasts to at least give a general guide. I don't expect to bat 1.000 here.

At this point, it appears the most snow will fall in western Whatcom, Skagit, and Snohomish counties, and in the eastern foothills of Snohomish and King County.

Here are some expected storm totals:

6 a.m. - 3 p.m. Wednesday

  • Northwest Interior (Whatcom, Skagit, San Juan Counties): 3-6"
  • Eastern Puget Sound Foothills (Above 500 feet from Issaquah east in King/Snohomish County): 2-5"
  • South-central Snohomish/North Central King County (Areas like Duvall, Snohomish and Monroe): 2-4"
  • Olympic Peninsula: 2-3"
  • North Coast: 2-3"
  • Everett area/West Snohomish County/Island County: 1-3"
  • Seattle-Bellevue Metro area: Trace-2" (maybe 3" in spots of 405 corridor)
  • Kitsap Peninsula: Trace-1"
  • Southwestern Washington: 1-3" (higher amounts in higher elevation)
  • South Coast: Trace-1"

3 p.m. - 11 p.m. Wednesday

Additional snow totals on top of what's fallen:

  • Northwest Interior: 1-2"
  • Olympic Peninsula: Trace-2"
  • North Coast: Trace-2"
  • Eastern Puget Sound Foothills: 2-5"
  • South-central Snohomish/North Central King County: 2-5"
  • Everett area/West Snohomish County/Island County: 2-4"
  • Seattle-Bellevue Metro area: 1-3"
  • Kitsap Peninsula: Trace-1"
  • Southwestern Washington: 2-5" (higher amounts in higher elevation)
  • South Coast: Trace-2"

Grand snow totals:

  • Northwest Interior: 4-8"
  • Olympic Peninsula: 2-6"
  • North Coast: 2-5"
  • Eastern Puget Sound Foothills: 4-10"
  • South-central Snohomish/North Central King County: 3-9"
  • Everett area/West Snohomish County/Island County: 3-6"
  • Seattle-Bellevue Metro area: 1-4"
  • Kitsap Peninsula: Trace-2"
  • Southwestern Washington: 2-6" (higher amounts in higher elevation)
  • South Coast: Trace-2"

The Warnings

A WINTER STORM WARNING is in effect from 4 a.m. Wednesday to 10 a.m. Thursday for all areas Everett north and the Eastern Puget Sound Lowlands. A WINTER STORM WATCH remains in effect for the rest of the area, only because those areas either are expecting under 4", or the snow is due in later. A Warning in this case means 4" of snow or greater is highly likely. A Watch means conditions are possible for 4" or more of snow, but not certain. If they expect those areas will get less than 4", they'll probably get a lesser Snow Advisory or Winter Weather Advisory.

The Lowdown

The North Interior is a winner in the snow lottery as that appears to be where the bulk of the moisture will flow. It also looks like the Eastside and the foothills will also get a significant amount in a two-step punch -- perhaps 2-4" when the initial storm passes in the late morning (higher amounts toward the foothills, lesser toward the 405 corridor), and then another round of snow in an anticipated Convergence Zone in the early afternoon. More on that in a moment.

We are expecting less snow Seattle-Tacoma-Kitsap area in the first wave as the storm drifts by because we're expecting westerly winds which means we'll be shadowed a bit from the Olympic Mountains. That shadow becomes less effective as you head east, which is why the Eastside will likely see a little more snow than Seattle. Still, 1-2" is possible from Seattle/Tacoma west to the Olympics.

HOWEVER, as we said, once the storm passes, forecasting models show a secondary band of moisture -- it's sort of like a Convergence Zone, but not classic. But the results will be nearly the same in reintroducing snow to parts of the Puget Sound region around noon to early afternoon and possibly lasting into the evening and affecting the evening commute.

It looks like the Zone will form in its usual spot around southern Snohomish County around noon-ish, then hang there for a while, snowing a few inches. The Zone then shifts south through the Seattle-Bellevue corridor, bringing a burst of heavy snow here during the late afternoon/early evening time frame.

This could add an additional 2-4" west of Lake Washington and 2-5" east of the lake, depending on how intense the zone in and how long it hangs over you neighborhood. But I'd hedge the higher totals in southern Snohomish and northern King Counties, with the highest totals over toward the eastern foothills northern King and southern Snohomish County (like Snohomish, Monroe, Index, Duvall), and the lower totals Seattle Metro, south to about Renton, (The Zone shouldn't go much farther south than that before fizzling.)

Keep in mind - that's on top of whatever falls in the morning though. And also keep in mind that, as usual, this is an incredibly complex situation, and these systems always have a few surprises.

Our original snow band is expected to move into Olympia and then Southwestern Washington Wednesday afternoon and into the evening and early night, with perhaps 2-3" as a general rule in many spots, possibly more toward the Cascades and Willapa Hills; lesser in the Chehalis Valley. The south coast may not accumulate snow at all and could actually just see rain or a mix, or maybe an early inch but a switchover.

Caveats

The storm will bring in a little bit of milder air off the ocean. This will likely not have much affect in the morning, but some models do think the area from Seattle south might drift a little over freezing around midday -- perhaps when the first wave passes through. This could be a pretty good fake out because I can see a scenario where we might change to a mix or perhaps a brief rain in the Seattle lowlands when that first wave passes and the snow level perhaps drifts up to 200-300 feet.

HOWEVER! When that second wave comes, it'll be intense enough to drive the snow levels back down to the surface. So if it does appear to rain or mix at 1-2 p.m., don't think it's all over because we will still likely see lowland snow in the late afternoon/evening when the next wave comes through.

This milder air might also do some tricks changing the snow to rain and back in Southwestern Washington and the coast, where it might warm up enough during the day to be rain, then change back to snow after dark. So be on guard.

Any mild air that does make it here will be quickly obliterated Wednesday night because forecasting models continue to show another reinforcing shot of arctic air moving in late Wednesday and starting up the Fraser Winds again near Bellingham to 45-50 mph and sending another wave of cold air rolling back into Western Washington. Lows Wednesday night are expected to drop down well into the 20s, so whatever falls Wednesday will likely freeze overnight.

We could see some lingering snow showers Thursday, 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 13-20 range.

Friday should be a lot like today -- sunny but continued cold -- possibly a few degrees colder than this current spell -- with highs 27-31.

Forecasting models are still debating what to do with the weekend, but are leaning more and more of Saturday being dry with highs in the low 30s. We then have an incoming storm for Saturday night or Sunday. Hints are now that this storm is a bit milder than before, so this could be a classic heavy snow-to-rain event. We'll have to see, but travel on Sunday could be very treacherous as well.

Maybe Not So Cold For So Long

Long range models have changed their tune a bit for Christmas week -- still keeping us cold, but not as cold as before, with the bulk of the arctic air drifting east into central Canada, allowing a bit more of an over-water track for the jet stream. That would likely mean snow levels of around 1,000-1,500 feet instead of sea level, making it rain in the lowlands but still snow in the mountains at times through next week.

For holiday travelers and skiers, that might just be the best gift of all :)

Timeline of Expected Events

Here's a quick synopsis of a time line for Wednesday as of late Tuesday morning. Of course, subject to change :)

Midnight -4 a.m.:

Snow begins up near the Canadian border and begins to sink south. Note that there is about a 3-hour discrepancy between two models as to when the snow begins -- one more around midnight, the other around 3 a.m.. The timelines listed here are leaning the earlier scenario, but be advised we might need to push these back a couple hours.

4 a.m. - 9 a.m.:

Snow begins to fall in the Puget Sound area.

9 a.m. - 1 p.m.:

Snow falls steadily through the region, then tapers off from the north toward early afternoon. It might possibly switch to mix/rain at the tail end.

1 p.m. - 4 p.m.

Convergence Zone starting to develop in Snohomish County and snow level returns to sea level here. Snow probably tapers off in the greater Seattle area and everywhere else north of Seattle outside the Zone; Earlier band of snow now starts to reach southwestern Washington.

4 p.m. - 9 p.m.

Convergence Zone drifts south over the Central Puget Sound/greater Seattle-Bellevue area. Snow level returns to sea level in the area, and a new round of snow falls -- possibly 2-4". Snow and/or rain is also falling in Southwestern Washington, but changing back to snow after sunset.

9 p.m. - 1 a.m.

Steady snow is done in the greater Puget Sound area, but we'll see a few random snow showers roaming around that could put down an additional 1". Snow continues in southern Washington/south coast, then tapers off as we pass midnight.

Other Areas

The mountains will also get hammered with snow. A Winter Storm Warning is in effect there until Thursday for 1-2 feet of snow there.

Down in Portland, they are expecting snow in the city Wednesday as well -- as much as 2-4", switch to a brief period of freezing rain, then switch back to snow with another 2-4" possible.

Over in Eastern Washington, Heavy snow is expected Wednesday as well -- as much as 3-7" in the lower elevations and 8-14" in the higher elevations. Highs there are only expected to reach the middle teens.

More Information

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