Aberdeen snowman by YouNews contributor lamboman53

SEATTLE -- With temperatures in the teens and 20s throughout the Puget Sound area -- and even single digits in Shelton -- drivers were met with another tricky commute Tuesday morning.

Anything that was wet Monday evening froze again overnight, and road crews are continuing to put down sand and de-icer.

The Seattle Department of transportation had eight de-icing trucks out overnight, and 30 crews were on duty beginning at about 8 a.m.

While most main roads are clear, the struggle continues to be on side streets and residential areas, where ice has covered roads for days. Even small hills are presenting a problem for drivers, who are slipping and skidding until they get to a cleared main road.

The hazardous driving conditions again forced dozens of school districts to delay classes (see complete list).

Here is a list low temperatures from Monday night (Updated for the late morning official numbers)

• Shelton: 9
• Arlington: 10
• Olympia: 12
• North Bend: 13
• Tacoma: 13
• Kelso: 14
• Port Angeles: 15
• Friday Harbor: 15
• Oak Harbor: 15
• Bremerton: 18
• Everett: 18
• Renton: 18
• Bellingham: 19
• Forks: 19
• Hoquiam: 20
• Seattle: 20
• Bellevue: 21
• Gig Harbor: 23

Tuesday night will see low temperatures in the mid- to upper 20s, but another storm is heading our way Wednesday, dropping in once again from the Gulf of Alaska, bringing another potential round of snow to the region.

A WINTER STORM WATCH is in effect for all of Western Washington from late Tuesday night through Wednesday night.

It looks like snow will begin around midnight -- possibly as early as 10-11 p.m. Tuesday -- in the north 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 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.

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 as that appears to be where the bulk of the moisture will flow. Snow totals here could reach 3-6" with perhaps some isolated higher amounts well east of I-5. Some snow is also likely in the northern islands (Whidbey, Camano, and San Juans) and along the northern Olympic Peninsula, but not as much as the I-5 areas-- maybe 1-3".

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 as the storm drifts by at first 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 Convergence Zone forming which will reintroduce snow to parts of the Puget Sound region around noon to early afternoon and possibly lasting into the evening and affecting the evening commute.

Convergence Zones are their own beast -- we can do a fairly good job of predicting if one will form, but once they do, they usually have a mind of their own. And historically speaking, some of the heaviest snows in Puget Sound have come from Convergence Zones.

As of this late morning, 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 could possibly shift south through the Seattle-Bellevue corridor, bringing a burst of heavy snow here during the late afternoon/early evening time frame. Snow totals could range from 1-5" 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 and lower totals Seattle 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 Southwestern Washington Wednesday afternoon and into the evening and early night, with perhaps Trace-3" in spots. The coast may not accumulate snow at all and could actually just see rain or a mix.

Therein lies this storm's potential monkey wrench -- some marine air. The storm itself is expected to track farther inland now and curve to the east over Skagit County. This will draw in some milder, ocean air to the coast -- perhaps getting them near 40 Wednesday -- and the southwest interior and even a bit down the Strait of Juan de Fuca.

Now, there's so much arctic air in place in the interior that snow is still a very high probability. At this juncture, it looks like there is more than enough arctic air here to support snow for several hours and even through the day in the interior. But that hint of marine wind is the monster lurking in the closet to thwart at least perhaps some of the higher forecasted snow totals. But on the coast and parts of the lower elevations of the southwest interior, where you're farther away from the cold air funnel near Bellingham, your arctic air is thinner and thus easier to warm up.

But that is likely just be a brief puff of "warmth", 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.

1 p.m. - 4 p.m.

Convergence Zone starting to develop in Snohomish County. 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 possibly drifts south over the Central Puget Sound/greater Seattle-Bellevue area. If so, new round of snow falls -- possibly 2"+. Snow is also falling in Southwestern Washington, but weakening and possibly changing to rain in the lower elevations. North interior is mostly done, save for a few random snow showers.

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/rain continues in southern Washington/south coast, then tapers off as we pass midnight.

More Information

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

• Pity poor Bellingham (wind chill info.)
  
• What records are in jeopardy?
  
• Ray Ramsey's forecast, 30 years ago today
  
• What was December 1990 like?
  
• See some chimpanzees' first snow storm
• How much snow fell across the region?
• Current map of how cold it is across North America
• What's my city's elevation?
• Great place to find current conditions
• A beer tornado?