Snow fell in some areas of Western Washington Monday morning, including downtown Seattle.
There are a lot of variables to this dynamic event, with snow expected at times through Monday evening.
There was some isolated snow or rain/snow mix on Sunday in spots like Enumclaw and Federal Way, as well as south Everett.
Snow was reported to have fallen in Mount Vernon and Granite Falls overnight.
Watching Monday morning
On Monday morning, it snowed in downtown Seattle shortly after 8 a.m.
It was cold enough in some areas for snow down to near sea level, and we're still watching all lowland locations. Shortly before 6 a.m., snow was falling in some areas including southwest Olympia, south Everett, Puyallup, Elma and Darrington. There have also been reports of snow from viewers including SeaTac, Renton, south Tacoma, Bellingham, Auburn, Bremerton, Chehalis and many others.
With a southwesterly wind, the temperature will be borderline for snow down to sea level, at least from Seattle south. I expect the snow level to be down to sea level across the north Sound and farther north to the Canadian border. Coastal locations will be borderline for snow as well.
"Chunky rain" (some snow mixed in with rain) or snow will fall through the Monday morning commute. Again, road surface temperatures will still be somewhat warm, so snow showers will melt to slush, especially on well-traveled roadways.
However, heavier snow showers can do two things: drag the snow level down to sea level and cause travel problems.
Until about noon Monday, about trace to two inches of snow could fall in areas at 500 feet or above. Areas Snohomish County could get as much as three inches.
Concern growing for late Monday and Monday night snow
The moisture available for widespread snow will dry up Monday afternoon, but I am watching the probability of stronger flow of cold air out of the Fraser River valley of British Columbia into Puget Sound Monday evening.
Strong flow of cold air can create a boundary -- like a cold front -- that moves south through the region. Along this southward-moving boundary, what residual moisture is available can be forced out of the air in a band of snow.
Some forecast models are suggesting this band could produce significant snow of several inches-- again from north to south -- Monday evening. This really is a wild card in the forecast, but one we will be watching closely because significant snowfall Monday evening would likely stick around into the Tuesday morning commute. Stay tuned!
We will watch for possible wintry weather later next week as well
Long-range signs point to the grip of the cold air weakening by Thursday as a moist, Pacific air mass moves in.
As the cold air is scoured out by the warmer airmass in patterns similar to that, snow occasionally falls before it turns to all rain in the lowlands.
But will the cold air mass "modify" -- or warm naturally -- before the moisture returns, just bringing cold rain?
We'll be covering all aspects of the weather on KIRO 7 News.
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