Unfortunately, you have hit the fire season nail on the head. We awoke in Seattle today to a "snow" of ash covering everything. There are currently 3 big fires in the WA Cascades: One on the backside of Mt. Rainier, one in the Cle Elum/Salmon La Sac area & one around Lake Chelan/Leavenworth. That covers a lot of good regional trails. I think you could still find some stuff around Naches/S of I-90 & near the Canadian Border. There are some great roads for exploring between Mt. Adams & Mt. St. Helens. The main forest road is paved but it's a lot of single lane winding through the woods & the winds are currently pushing the smoke to the NW which should leave this area relatively clear. A route up the backside of Helens would take you by Ape Cave & up to Spirit Lake. I believe Adams Fork Campground is in that area & it's one of Bigfoot Overland's favorite places.
Another WA area is the Olympic Peninsula. A loop around that is always interesting though I'm not sure there's a lot of 4x4 accessible trails.
Alternatively, OR really has a better forest roads network though our may want to save Tillamook SF for when you have less time(.
http://www.lastgreatroadtrip.com/wp-content/uploads/2009/03/TillamookOHVGuide2014.pdf). Make sure you meet OR's backcountry vehicle requirements for a shovel with 26" handle & either a certain quantity of water or a certain size fire extinguisher-I expect they are being pretty picky about that right now.
The area around Bend is nice for desert travel but probably pretty hot right now. There are some fun lava tubes to explore out that way. Further afield is Steen's Mtn & that region.
Here is a link with some classic NW trails (it has an OR page too)
http://www.nwjeepn.com/WAtrails.htm
& another
https://www.trailsoffroad.com/states/WA
Finally there are Backroads Discovery Routes in both WA & OR. JDunk has some nice YouTubes on what they are like. Here's a link for WA
Www.ridebdr.com/WABDR
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