Weather models suggesting changes to Wednesday's snow storm

SEATTLE -- Winter is set to continue its onslaught on Western Washington with more snow in the forecast Tuesday leading up to a major snow event on Wednesday. However, latest forecast model guidance shows some changes to Wednesday's forecast that could keep the snow around longer.

But in the short term, we are still dealing with some occasional snow showers as a weak weather disturbance passes by the area. Snow showers will be most frequent and heaviest in the southwest interior, along the coast and from Skagit County north to the Canadian border where Winter Storm Warnings remain in effect until 6 a.m. Tuesday for potentially 2-5 inches of snow in spots in those areas.

Outside those areas a general Winter Weather Advisory is in effect for random hit-and-miss accumulations of up to 1-3" both Monday night and Tuesday.

That includes the greater Seattle area, which along with Everett has been protected by snow showers from shadowing effects of the Olympic Mountains. But some showers could develop as the low progresses further away.

The snow in the forecast and on the ground has already prompted some schools to post delays and cancellations for Tuesday.

Snow showers will linger in the front's wake Tuesday afternoon and we'll be in another lull until Tuesday night when a much larger storm heads in. A Winter Storm Watch remains in effect for all of Western Washington for this Tuesday night/Wednesday storm.

Washington will be right in the battleground between a very warm air mass being pushed north from the tropics and a very cold, arctic air mass dropping south from Alaska. This will aid in storm development, but also means that a slight change in track is all the difference between whether you're on the warm side or cold side - and it's possible it could split the state in half north-south.

The general theme is for heavy snow to begin late Tuesday night or early Wednesday morning as the storm approaches, but latest forecast models generated Monday night are starting to paint a different evolution of the storm where the change over to rain is delayed or perhaps doesn't come at all.

Models indicate the storm will take a further south track, which would prevent warm, southerly winds from reaching the Seattle area and points north, and in fact would help draw in colder air from Canada. On the other hand, with the more southerly track, much less moisture would reach the far northern interior and spots like Bellingham could be left cold and relatively dry (but windy)

For the greater Seattle area, this is still a very snowy scenario with anywhere from 6-10" possible with isolated higher amounts, especially south of Seattle where areas could approach a foot or more. But if the new models are correct, the snow may continue to fall and stick around on the ground through Wednesday night and even into early Thursday morning with little or no rain to wash it away.

There are even some models hinting at a second shot of snow on Thursday as Seattle and points north remain in the cold air -- although much less moisture this time around and not quite as much snow.

Suffice to say, winter weather could be around for a while.

Other concerns

Depending on the storm's track, we could also be in for a period of strong, gusty winds through the day Wednesday as the storm progresses.

If the storm stays south, as models are trending, Whatcom and San Juan Counties could be in for a prolonged period of strong northeast winds out of the Fraser River Valley. If the storm goes north, much of the region could be in for a gusty Wednesday evening or night

And if we get the change from snow to rain, the problems likely won't end. We'll then have to deal with slushy messes and urban flooding as snow clogs storm drains. Some models indicate over an inch of rain could fall with this storm.

Forecast by region:

* Seattle, Tacoma, Bremerton: Period of snow possible late Monday into Tuesday morning, ranging from 1-3 inches with highest amounts on the hilltops away from water. Lull afternoon into evening Tuesday, then big snow arrives Tuesday night into Wednesday and Wednesday night. 6-10 inches possible there until changeover to rain, if it occurs. If storm does push north and warm air arrives, expect heavy rain and gusty winds.

(Note for Kitsap County: You've been in the relative lull due to Olympic snow shadowing, but Hood Canal area likely to get among the worst of Wednesday's storm with 10-14 inches likely, perhaps more.)

* Cascade Foothills & Island & Snohomish County Convergence Zone area (Everett and vicinity): Potential for band of snow in the convergence zone Monday night that could bring 2-4. There is still some uncertainty to this front, so not a slam dunk. Heavy snow begins anew Tuesday night through Wednesday. Snow totals 6-10" or more.

* Whatcom, Skagit, San Juan Counties: Snow showers, heavy at times, for MOnday night into Tuesday with 2-5" of new snow possible. Gusty northeast winds to 20-35 mph developing by late Monday night as well. Relative lull in snow Tuesday with minor accumulations, then snow returns early Wednesday morning with winds gusting again to 30-40 mph. Latest models back off on amount of moisture that reaches here Wednesday, but what does fall would stay as into Thursday morning and may or may not change to rain. Snow totals in Wednesday storm are now highly variable depending on storm track.

* Strait of Juan de Fuca area: A relative lull Monday night with just a few scattered snow showers. More snow expected Tuesday and Tuesday to the tune of 1-3" with winds still gusting to 20-25 mph. Heavy snow begins toward dawn Wednesday. Snow likely to remain until around midnight Thursday morning before changing over, if it does. Snow totals could be 6-10 inches.

* Coast: Snow showers Monday night with another 2-5 inches possible (mainly away from beaches). Relative lull Tuesday then snow develops Tuesday night into Wednesday. Changeover to rain will happen from south to north along the coast as Wednesday afternoon progresses. Snow totals range from 6-14 inches.

* Southwest Interior: Snow at times with 2-4" possible by Tuesday morning. Then snow will develop late Tuesday night with the big storm, although this area will be among the first to change over to rain, likely around midday Wednesday. Still, snow totals could reach 6-14 inches.

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