Another smoke and fire dependent route recommendation.
Take train north to Seattle and east to Whitefish. Then do the National Parks routes. Since you are in the US, no better place to tour than Glacier and Yellowstone Parks. Tourist season is winding down (after Labor Day) and the roads should be nice and quiet.
Heavily dependent. WA 20 sounds like it's out. Significant fire activity near Winthrop, Twisp, Okanogon and Omak, WA. If you look at the Winthrop KOA web site there is an alter noting that while the campground is open, portions of WA 20 east and west of the facility are closed.
There is also a fire near Chelan, WA. Also, one near John Day, OR, which I believe is on the TransAm route, has grown and could get bigger: