With the Apple Cup typically scheduled for the final college football weekend of the year, the weather in Pullman is usually a topic for discussion when the game is on the Palouse. The drive over the Cascades for many of the alumni and students is also a cause for concern. Your trip over to Pullman looks jut dandy; the weather once you get there though looks wet then cold and we may see some snowflakes.
First, lets start with your drive over from the Seattle area. At the pass level, you should be just fine using Snoqualmie or Stevens with the forecasted snow level at 5,000 feet or above. The road will be bare and wet but the rain could be falling quite heavily at times. If you're coming from the Tri-Cities, things look a little better with just a chance of rain. Just a slightly better chance of rain if you're coming from Spokane.
Once everyone gets to Pullman though, that's when things get downright cold. The National Weather Service is expecting much below normal temperatures for Saturday and Sunday with a high on Saturday just getting to freezing and an overnight low that is forecasted to end up at 17. That means kickoff temps will likely hover somewhere in the lower to mid-20s.
As for the possibility of snow, the best chance comes during the day on Saturday with an inch or two of accumulation possible. It'll taper off by Saturday night jut leaving you cold. Still, we've all seen a forecast for Pullman to get an inch or two and it ends up buried.
The drive back after the game looks dry but cold again no matter where you're headed. Things will be cold across the state until at least Tuesday.