Hello pezzino,

With that much time at hand for the trip, you can very likely simply head west on I-94/I-90 and wait out any bad weather in the MT and WA passes. The MT passes, in particular, are relatively low in elevation. The balance of I-90 in MT seldom exceeds 4,100'. Excepting to avoid clearly identified severe localized weather events, I'd choose I-90 over I-80 or even I-70 and I-40.

Do some research involving real-time weather radar (like Weather.com) for Bozeman, Butte, and Thompson Falls, MT. Watch weather systems as they approach, impact, and depart. Simultaneously watch the RWIS real-time webcams for the MT passes on the MT DOT website. Also look at some of the low-lying webcams along the I-90 corridor. I think you'll be pleasantly surprised at how good the "going" is virtually all of the time away from the passes, and within mere hours of the departure of an event in the passes.

Foy