The Puget Sound Convergence.

 

Last week’s epic snow was due to the position of Stevens Pass, to the Puget Sound Convergence Zone. When the wind hits the northern coast of Washington directly from the west, it splits around the Olympic Mountains and “converges” over Puget Sound. Just like water flowing around a rock, it eddies directly behind the mountain (Sequim Wa. the driest place in western Wa) and accelerates on it edges. The Hwy 2 /river gorge network is positioned perfectly to augment the acceleration. The wind and precipitation get shoved up through the Pass where temperatures and orographics are enhanced.
        Wind direction is the feature to look for for the development of the convergence zone.  If the winds hit the Olympic Mountains straight from the west, Stevens Pass will achieve convergence conditions. If they come from the NW, then Snoqualmie gets the convergence.    You can see below the winds "bending" around the mountains.