The scariest part of the drive from Pullman to the west side is often before the pass. If the pass is open, there’s a good chance you can get in the tracks of some semi and plod along at 35 pretty safely. But between Pullman and Ellensburg can get super dodgy. I’d pay attention to that forecast and possibly reroute to Spokane first so you can take I-90 all the way to Seattle.