9 PM Update: The latest run (WRF-GFS) is virtually identical to this morning's forecast. This should be a good storm, but we are not talking of an event like the Chanukah Eve or Inauguration Day windstorms. The NWS has just put out an ominous bulletin on their web site and to show it is serious it is all red.
An unusually strong spring storm is approaching and will hit tomorrow. It could end up being the strongest winds in several months for the Northwest lowlands. And we have the added complication of some trees starting to leaf out--which makes them more vulnerable to a strong blow.
Let me show you a series of surface pressure charts for tomorrow, produced by the UW WRF numerical prediction system. The maps are for 8 AM, 11 AM, 2 PM, and 5 PM tomorrow.
A perfect track for strong winds over Puget Sound and the WA coast--right across the NW corner of the Olympic Peninsula (see my book for information about optimal storm tracks). The largest pressure gradient and strongest winds will be later in the afternoon...not the morning...for Seattle and vicinity. What kind of winds? Would not be surprised to see 40-60 kts over Puget Sound and 20-40 kts over land. Expect some power outages.
And the fun doesn't end there! As the low moves past us, there will be a westerly surge through the Strait of Juan de Fuca that will hit Whidbey, northern Olympic Peninsula, and southern San Juans.
You want more? You got it! Moderate to heavy precipitation will strike the region, with 2-5 inches of precipitable water in the mountains. Guess what, a lot of that will be in the form of snow...with some areas getting several feet. Check the 24h snowfall ending 5 AM Saturday below. Get those skis ready! But a warning--the avalanche danger is going to be substantial when this is all over.