We are now coming to the close of the first act of today's weather drama. To bring up-to-date with the plot.....
With westerly to NW central Puget Sound has been rainshadowed by the Olympics and virtually nothing has fallen...except for some ice pellet shows in a few locations. In fact, some places had blue skies! On the other hand, Skagit County and a zone extending westward across Whidbey and the San Juans have been hammered--some folks have gotten 5-6 inches of snow. See images at Friday Harbor and Anacortes.
And snowshowers have hit the south Sound south of Tacoma. The relatively mild temperatures (30s) have allowed roadways to be relatively decent even where snow has fallen....this IS late February!
But things are changing. As the low pressure system in the coastal water moves southward from Vancouver Island, the rainshadowing is weakening...as the flow aloft lessens and turns more to the southwest. Already we can see increased snowshowers moving into the south Sound and the rainshadowing (yes really snowshadowing) has lessened in the high-res visible satellite imagery. The pressure difference between Bellingham and the NW interior has increased and NE flow is increasing at Bellingham. The pressure difference between Bellingham and and Olympia has reversed, setting up the movement of northerly flow into the Sound. And it is at the interface between northerly flow and countervailing southerly flow where the real lowland action should happen. This is the big threat for the Puget Sound lowlands and we need to watch this afternoon whether it develops. If it doesn't the commute will be fine. If it does, you will have to deal with a slushy layer on the roadway.
This is all very complex and determined by the position and strength of the low, and the strength of the rainshadowing.
Over the short term, the zone from Everett to Tacoma is fine...but conditions should worsen after 2-3 PM. But at this point I don't foresee any major icing situation over Puget Sound roadways for commute time tonight--something I have heard incessantly on some media outlets. THIS WILL NOT BE LIKE NOV 22ND. No severe sudden freeze during the commute home.
You are now reading the article11 AM NOWCAST: ACT II with the link address http://www.outsiderla.me/2011/02/11-am-nowcast-act-ii.html