stickysharp,
Most of the rivers in Western Washington have Summer runs. The OP rivers fish well from what I here. I spend time on the Sky because it's close to home and work so I can hit it for an hour before work a couple days a week. Also take 3 or 4 days off to fish the Snake in Eastern Washington and the Clearwater in Idaho in October.
Best bet is to talk to your favorite fly shop they will let you know a little more about the rivers in your area.
I don't even start my summer fishing to the water warms up to 55 degrees. Fish will come to the surface below that temp but you will be casting till your arm falls off. Usually if I do go in June I fish sinktips and thats called winter fishing for summer fish in my book.
Good luck, there is nothing better in the whole NW than a steelhead that comes to the surface for the take.