I have not seen such persistent fog in my dozen years here.
Cliff Mass thinks this is a highly significant inversion pattern, too: http://cliffmass.blogspot.com/
I took my mom up to Mt. Rainier yesterday, climbing above the gloom into the sun. (At one point I made her laugh: we passed a sign that said "31 mi. to Paradise," and I said, "Or even closer if I don't keep my eyes on the road.") The chalkboard at the Paradise Visitor's Center predicted a high there of 63* and freezing level at 11,500'.
Here's the most recent 3 mo. climate forecast: http://www.climate.washington.edu/outlook.html. Winter isn't over.