We drove on I-15 shortly after a freak late spring snowstorm hit Utah pretty hard 10 or so years ago, from just north of St. George to where it turns into I-84. The winds were really high on a few sections of the freeway around Ogden, and a couple of tractor trailers were blown over, but otherwise it was fine.
At the end of I-15, you have two routes to choose from. The I-84 route may be less messy than going up to Butte, just because that way you're skirting around the mountains for the most part. The one place to watch on that route is a place called Cabbage Hill, near Pendleton, but generally they keep it pretty clear.
Here are some websites to help you out:
WSDOT weather and traffic info:
WSDOT - Statewide Traveler Information
ODOT weather and traffic info:
TripCheck - Road Cams, Road & Weather Conditions in Oregon - ODOT
Idaho Transportation Department weather and traffic info:
Idaho Transportation Department - Division of Highways