What's special technic to catch whitefish in winter (nymphing I guess?) and which rivers around Seattle have decent populations of whitefish (Sky,Stilly,Snoqualmie,Green?)
The best way to catch whitefish is with a worm on the bottom. But if you want to fly fish for them, I'll bet that a San Juan Worm would work. I've heard that if fish are spawning in the river you're fishing, egg patterns (glo bugs) work well.
Hope this helps,