Winter Storm Watches now posted for lowlands

Winter Storm Watches now posted for lowlands
Plows and sand trucks are being readied in advance of the storm.
This forecast is now being updated as a new, separate story. Here is the link to the latest version of this forecast

The storm has been in the forecast for days, and now it's close enough that some severe weather advisories and warnings are being issued. And some of them are quite impressive. For starters, a Winter Storm Watch is in effect for all of the Western Washington lowlands.

New as of Thursday night is the storm will be coming ashore...somewhere. Officially, the range of tracks is between Neah Bay and Long Beach, but pardon us if it feels like the range is between San Francisco and Ketchikan, because the small deviation in the forecasted track has large ramifications on the weather Friday and Saturday.

One model has it now back to coming inland around Foks and coming down the Strait of Juan de Fuca. Another has it still south of Hoquaim. The former means a potentially windy day across most of the region, the latter more localized wind and a better chance of snow Friday night.

With the uncertainty, we have to forecast for the worst and hope for the best, so take these warnings as guidance to be prepared of what could happen.  In fact, this could be one of the most complex forecasts we've had to decipher in quite some time.

As of 11pm Thursday, here's the rundown:

A WINTER STORM WATCH has been expanded to cover all of the western Washington lowlands, including the greater Seattle metro area, from Friday afternoon through Friday night.

However, this is a broadbrush watch, and it appears there are plenty of places that still would be too warm to snow. On the other hand, there are some places that could see 3-8" of snow overnight Friday into early Saturday morning, so the watch is for everyone as it's too overwhelming to try and rule out spots here and there.

(A watch means that chances are 50-50 or better that these conditions could occur.  If they do occur or become imminent, it is upgraded to a warning.)

Speaking of which, A WINTER STORM WARNING remains in effect for the Cascades and Olympics from Noon Friday through 6 a.m. Saturday. Expect heavy snow and strong winds in the passes with snow accumulations as much as 1-2 feet.

I've had a lot of people e-mail me about planning to get over the passes tomorrow, and asking when would be a good time. The answer is, as soon as possible -- definitely before noon Friday. Anytime after that and you are going to run into miserable and very likely dangerous driving conditions. If it's a planned weekend trip, pack for a few extra days as road conditions will be very icy across the state Sunday through next week.

A HIGH WIND WARNING is now in effect for the coast from 10 am Friday through 4 am Saturday.

A HIGH WIND WATCH remains in effect from Friday afternoon through Friday night for the Strait of Juan de Fuca, and San Juan Islands/Western Whatcom County area. This has some geographic variables as to when and how fast. Details coming below.

A potent storm is expected to intensify as it drops down out of the Gulf of Alaska and makes landfall on the Washington coast. In fact, it's still hardly even there as of Thursday evening, but all forecast models are consistent in having a low pressure system "bomb" -- i.e. undergo rapid intensification, being fed by the cold air to our north. Models predict the storm will intensify as much as 40 mb in 30 hours! (That's like going from 30.24" to 28.94" in just over a day.)

But with the storm still in the infant stages Thursday evening, we can't exactly track it with the satellite to see if the models are right, so we have some blind faith in the computers. (But all computers are consistent in its development, and the atmospheric dynamics are ripe for it to occur.)

But as I mentioned earlier, it's as if Mother Nature is playing 3 Card Monte with the storm, tweaking the path and expected landfall a bit with each forecast run. And each minor tweak in the path represents a major shift in what could and will happen. Add in potential lowland snow, and you can imagine the difficulty in this forecast.

Just to make things more interesting, some late Thursday evening models seem to drift the track back a little more to the north. (If you ever meet me someday, you'll wonder: "Gee, I don't remember you having such gray hair in your blog bio photo...")

But here's what we've got as of Thursday late evening.  This is still based on a central to southern Washington landfall. A more northern landfall would increase strong wind threats in the Puget Sound and Southwestern Washington areas Friday late afternoon and evening, and wind advisories or warnings might need to be issued during the day.

Friday Morning

Rain developing in lowlands. Winds increasing along the coast. Still OK in the passes.

Friday Noon-3 p.m.

* Wind will greatly increase along the coast. It will begin as a south wind of 20-30 mph, gusting as high as 45 mph through about early afternoon. It will then switch to some sort of a westerly component once the low passes in the afternoon and be 35-45 mph gusting as high as 60 mph.

* Snow begins to fall in the mountains, increasing in intensity through the early afternoon hours.

* Inland -- still just rainy.

Friday 3-6 p.m.

As the low passes inland, it will increase the north wind and start pulling in some cold air from B.C. into the Western Washington lowlands. This is assuming the south/central coast landfall.

What that means: Expect the possibility of snow to near sea level along the Hood Canal and the eastern slopes of the Olympic Mountains (like along Highway 101 between Hoodsport and Brinnon). Could see as much as 1-2" by the end of this time frame.

* For the Puget Sound area, this period is still just rainy, but could be changing to a mix in the higher spots. Wind would not be a factor here with a far southerly track, but could be gusting as high as 40-50 mph if the storm comes in farther north, so be prepared for possibly strong winds Friday afternoon in the greater Puget Sound region.

* Winds are still a concern along the coast (West 35-45, gust 60), and now along the Strait of Juan de Fuca, although not as bad as earlier feared -- perhaps westerly gusts to 35-40 mph -- again (say it with me) depending on the track.

* The mountains will be getting hammered with snow and gusty winds. They don't care where the storm comes inland.

Friday 6 p.m.- 10 p.m.

* Rain possibly changes to slushy snow as snow levels drop to about 600-800 feet, but heavier showers could drag snow lower. This could begin at the tail end of the normal commute Friday, but I still think the main Seattle metro commuting corridors should be OK -- for one, the road temperatures will be warm. But please keep an eye to forecasts. This is a very difficult situation that is not really going according to a typical snow event script (of course, which one does?). A more northerly storm track kills off this particular snow scenario, but then increases the wind potential. (Or, the storm could come right over Seattle, and ironically, we don't get much of either.)

* This now could also feature heavy snow in the Whatcom County/Skagit County/San Juan & Camano islands areas.  This area has been added to the Winter Storm Watch and some spots could see 4-8" in a worse case scenario by late Friday night.

* Snow continues to fall heavily in the mountains. Gusty winds up there make near whiteout conditions. Snow also possible still in Hood Canal / east Jefferson County area mentioned above.

* Winds continue on the coast, but slowly taper off. Winds taper off in Strait.

Friday 10 p.m. - Saturday 6 a.m.

* Scattered showers of rain, snow or mix.

* Potential Convergence Zone between North Seattle and Everett and points east, could be snow in areas above 400 feet. Possible accumulations of nothing to 5", depending on cold air and intensity of event.

* Best chance for snow showers elsewhere: Kitsap Peninsula, Northern Olympic Peninsula (Forks through Port Angeles and Sequim to Discovery Bay), Cascade foothills above 500 feet, North Coast, Southwest Interior above 700 feet. Accumulations could be Trace to 6" depending on intensity of showers, with higher amounts in the higher elevations. Again, not everyone will see 6".

* As mentioned earlier, lowland snow also possible in Skagit, Whatcom County and the islands, and potential amounts have been raised to 4-8" in the upper range; higher amounts with elevation. However, a more northerly storm track, and that limits this event.

* General rain or mix in Seattle-Tacoma-Bellevue lowlands, but could see brief dusting in heavier showers and on Seattle hilltops.

* Wind begins to increase in Fraser River Outflow, could see northeast winds up to 35-45 mph, gusting as high as 60 mph across western Whatcom County and the San Juan Islands (henceforth referred to as the "Fraser Outflow area", and I get 20 bonus points for using "henceforth" in this story.)

Saturday 6 a.m. to Noon:

A second, reinforcing wave of arctic air forms in the interior of British Columbia. A trough of low pressure just off shore will help begin to draw that cold air out of the Fraser River Valley through northern Whatcom County and into Western Washington. That trough will also provide moisture in the form of random scattered showers.

So generally speaking, this period will feature scattered hit-and-miss rain or snow showers, with possible lingering Convergence Zone snow showers. Showers in the from of snow will be most prevalent in areas that got them Friday night, but accumulations should be light. Still likely rain or mix in the sea level areas.

* Very windy and cold still in Fraser Outflow area. Northeast winds up to 35-45 mph, gusting as high as 60 mph across western Whatcom County and the San Juan Islands. Wind chills dip to single digits.

Saturday Noon-8 p.m.

As that cold air sags south out of Bellingham, it could trigger an arctic front along the boundary of the cold air and really cold air. This could bring a period of snow that could drop 1-2" across the area. Air behind arctic front would be very cold and would likely freeze any snow to roadway surfaces. Temperatures drop from mid 30s in the morning into the 20s from north to south as the day progresses.

* Still windy and very cold in Fraser Outflow area. Wind chills nearing 0.

Saturday night:

Arctic air is now in place and getting deeper. Meanwhile, that trough will continue to toss scattered showers our way across the entire region. Snow levels at sea level so all showers in the form of snow. Accumulations in individual showers range from Trace-2".

Continued strong northeast wind in the Fraser Outflow to 50-60 mph in gusts. We'll also see brisk north winds fan out across the Puget Sound area and northern Olympic Peninsula to 15-30 mph.

That will drop wind chills near Bellingham near or below zero, and to around 10 in the Puget Sound area. Actual temperatures will drop into the teens to low 20s. Snowy roads ice over.

Sunday:

Similar to Saturday Night -- hit-and-miss snow showers will continue across entire region, with brisk north winds, increasing as you go farther north.

Any kind of snow or water on the road will be solid ice by now, making driving treacherous.

Highs will only be in the upper 20s to low 30s most areas, but only low-mid 20s near Bellingham. Wind chills in Bellingham near or below zero, and in the teens elsewhere.

Sunday night:

The trough moves away and showers taper off. As skies clear, temperatures plummet even farther. Lows will drop into 12-17 range with brisk north wind continuing.

Monday-Wednesday

It's mostly sunny, and crisp, but continued very cold as arctic air just keeps pouring in via the Fraser Valley. By now, Bellingham residents will qualify for Minnesota residency. Highs through the period will only reach the low-mid 20s, and lows will range from 10-17, making this potentially the coldest and longest arctic outbreak since 1990.

Morning commutes will be likely snarled by widespread ice, and I expect several school delays or closures. We can hope that as the week progresses the sun will at least melt and dry up whatever snow is out there and get slightly improving conditions as we go along.

On the other hand, get your cameras ready. I expect some truly spectacular city shots with the mountains crystal clear and full of new snow. And years from now, you'll forget how cold you were.

Beyond that, long range models continue to disagree with how long this cold air sticks around, and we'll have to watch as some models have occasionally hinted at some light snow Wednesday into Thursday. We'll see, but it's possible this cold air lasts through the week and into the following week.

By the way, as cold as it'll be here, it'll be much worse in Eastern Washington. Highs Sunday through Wednesday will be in the 8-13 degree range, with lows dropping as low as 15 below zero in Spokane Tuesday morning. (OK, maybe they get first priority for Minnesota residency.)

Stay warm out there!