Alrighty... i can't say i've got the 509 dialed in, but within an hour or two of WSU you've got a few options.. You're a bit late for the snake- the mainstem from tri cities to lewiston is a fall game, and I did pretty good on them fishing bobbers and shrimp around lower granite ( we'll get more on that subject when the time comes around again next year ), and theres boat and bank spots all up and down the big riv. Other options which are still open right now are 1. Mainstem snake above lewiston (heller bar) 2. Grande Ronde 3. Clearwater. I'm not familiar but theres always the lower palouse and tucannon that kick out some steelhead too...
1. Mainstem snake above lewiston
Headed past asotin about a half hour, you'll come to the end of the line at heller bar. This is some big heavy water at the mouth of the grande ronde, but it has some pretty good bank access, and even though the best fishing is in the fall, you can still pick up fish here through the spring. You'll be able to drift fish, use hardware, and bob/jig.
2. Grande Ronde
South of pullman about an hour you'll find lots of water (and steelhead too) from where the highway meets the river at boggans oasis all the way upstream on a little road to the oregon border. Fish trickle in in the early fall, and the fishing gets decent through late fall and early winter. You'll be able to catch fish here for a few more months, but you'll have to work harder for some bright fish. This is a smaller river (compared to the snake!), and you'll be able to use about anything you want. Method of choice by the locals is usually the bober and jig, and i have found it to be successful on one occasion this winter. The view is awesome even if the fish aren't biting, and there is plenty of shoulder room especially this time of the year. For a quick report to see how the river is doing, call the guys down at boggans oasis @ 509-256-3372. They'l let you know everything you need to hear before heading down....
The clearwater from the mouth all the way up past the N fork and kamiah get a big run of steelhead from august to early spring, and the river is especially known for the "B" run fish which consistently work the limits of the double digits. Being in idaho, you'll need an idaho license. This is gonna cost you around 80 bucks for non res, plus you'll need the 12 dollar steelhead card. Yeah, its alot- and it sucks because IDFG even charges their employees full price! ( i tried! ) You could always go for a short term license which will save you some $$ too. Anyways, earlier in the season (august, sepetember ), alot of those snake fish and some clearwater fish later on stage right in the lower mile or two of the river where they seek thermal refuge in the colder waters of the clearwater. Here they are caught by boat or sometimes bank with plugs, shrimp, jigs- and for a real kick in the but try lite up plugs at night! Upstream of lewiston along HWY 12 you'll come out of the backup from lower granite lake and into the free flowing stretch of the clearwater. Theres great access and holes all the way up the river to where it meets the lochsa, but for this time of the year, you'll want to focus more upstream. Best bets would be around the north fork and orifino, and upstream. You're probably best off fishing jigs right now, or maybe drift some eggs.
Lots of water to explore, and the best way to find some fish is to get out there and check out what the area has to offer! Theres always people around to point you in the right direction, and if you're completely stumped- stop by black sheep sporting goods in lewiston and those guys usually have the down-low on how fishing has been.