The administration of Northern Wisconsin is so efficient in terms of snow that at most, we'd have two hour bus delays. Everyone and their brother own a plow attachment to their truck. Things are just that fucking efficient here, snowfall needs to be crazy for us to be phased by it.
Now snap-freezes, those are a different story. Essentially that the diesel fuel used by the buses will gunk up and gel in low temperatures. I remember a time in college when my car battery froze to the frame of my car and I had get it towed into a shop just to be thawed.
Wind is the other threat here, combined with our rain and we'll get freezing sleet that can really fuck with anyone unlucky enough to be caught outside.