Hello bthorn31,

The corridors traversed by I-90 in MT and I-80 in WY are but a few hundred miles apart, and somewhat localized weather conditions are required for one to be under vastly different conditions than the other.

I share the opinion of Southwest Dave that the best bet is to look at forecasts in the time frame immediately preceding your trip and choose your route accordingly. That said, I would be very surprised to find snow in amounts and for durations sufficient to materially affect traffic flow in October.

Of the two segments, I vastly prefer I-90 through northeastern WY and all the way across MT. Once you reach Billings, it follows the Yellowstone River to Livingston with mountain ranges off in the distance on both sides. It goes up and over a couple of very scenic passes west of Livingston, then a long, gentle section west of Butte to Missoula, where it's in broad valleys flanked by forested mountain ranges with snowcapped peaks. Excepting I-70 through CO, I'd rate I-90 in MT the most scenic of Lower 48 Interstates in terms of alpine scenery.

Have fun planning and taking your RoadTrip!

Foy