Here are the max gusts for the 24h ending 7 PM Monday for a domain stretching from southern Puget Sound to Walla Qalla. The red numbers are winds over 50 mph.
In the spring, the winds increase rapidly when cool, Pacific air floods western Washington and Oregon as it did on late Saturday night. Cool air is denser than warm air and is associated with higher pressure. With the Cascades blocking much of cooler air on the west side, a large pressure difference (or gradient) develops across the Cascades. In addition, the flux of cool air is often forced by an upper trough, which results in pressure declines east of the Cascades as it passes through.
Let me illustrate the development of a large pressure gradient across the Cascades with the sea level pressure forecasts for 8 AM Sunday. The shading shows low-level temperatures, with green temperatures being cooler and orange/red warmer. You can see the contrast in air temperature across the Cascades. The solid lines are isobars (lines of constant pressure). You note a lot of lines (strong pressure gradient) across the Cascades. Such large pressure gradients produce strong winds as air accelerates from high to low pressure, particularly within the lower areas of the central Cascades.
Modern numerical models run at high resolution can forecast the strong winds along the eastern slopes of the Cascades fairly well. Here is the sustained wind speed prediction for 8 AM on Sunday from the UW high resolution WRF model. You see the strong winds along the lower Cascade slopes?
And here is a blow-up from our uber-resolution (4/3 km grid spacing) WRF model forecasts for gusts at the same time. The model had isolated locations reaching 60 knots--not bad.
This is the windy season on the eastern Cascade slopes--with cool marine air on the west side and the eastern side warming rapidly (producing low pressure). Wind power season.
Major news: the proposed coal terminal near Cherry Point (near Bellingham) has been stopped by the US Army Corps of Engineers. Their reason: to honor the treaty rights of the Lummi tribe to use those waters. This is a huge victory for those concerned about coal dust, traffic backups near rail crossings, and the climatic effects of sending huge amounts of coal to Asia.