The Cowlitz should be heating up in the next few weeks, try Blue Creek from the bank, can get crazy down there though.
If you don't mind fishing with lots of people, this is as good of a place as any to go catch a steelhead or two. The Olympic Peninsula rivers are also just heating up, mainly wild fish, which have to be released in most of the rivers. When these rivers are in shape, they offer a lot of good bank access on several different rivers with a great opportunity to catch fish.
Other than that, most all rivers except Columbia tributaries and the Cowlitz will close the end of March or April 15 and then open again June 1. When the Skykomish opens June 1, it can have good summer run steelhead fishing from Monroe up river to the hatchery. The Skagit from Rockport up to the mouth of the Cascade at Marblemount will be open for hatchery chinook, and can be good at times. You can always target Dolly Vardon up there when it opens as well. I don't suggest keeping those fish but they can be fun to catch.
Always always always read the regs before you head to any river. Rules not only change annually but can change on a moments notice if a run of fish isn't showing up as expected. You need to know what rivers are open, which sections of those rivers are open, and what species those sections are open for.
