Having lived in the PNW for years I have to say all season or summer tires will work just fine. Also if you have a AWD vehicle for the Winters, use that.
I just cannot and would not justify buying tires living in California, Oregon, and Washington. Again the Winters were pretty weak, regardless. Have any of you cats lived in Barrow or Nome AK? That gets pretty bad.
Now I am on the East Coast I still will run Summer tires on the M3 and All season tires on the X5. If the roads were as bad as Alaska I will take a week off from work. Much safer and smarter. No need for my lifestyle to waste thousands of dollars or even hundreds on something that I will not benefit at all. Sorry just been in extreme condition countries and states and the PNW is not on that list.