The drive from Twin Falls to Glendive was annoying but tolerable. It rained a lot, though there were periods of sun. Sadly it was cloudy when I went through Butte, so I couldn't see the giant Butte'er Jesus on the hill (the internets tell me it's actually a statue of Mary, but it's not easy to tell from the interstate).
The drive from Glendive to Winnipeg was a lot rainier. I think I passed a tornado or two after Grand Forks, and had lightning strike objects within 200ft of the car at least 3 times. I also just barely made it through Morris, as the road through town had started flooding, and was at least 8 inches deep by the time I waded my car through it.
And, to cap it all off, the rain was bad enough that it even stripped some of the paint off my hubcaps.