Why would you try to back up a hill with RWD in the snow?? I once couldn't get my M coupe to go up a steep hill on cold tires in the DRY! Summer tires just got hard as a rock and spun/hopped.
If you get moist snow on >freezing roads, it can get slick as ice. The colder it gets, the colder the snow gets, and the drier the snow gets, the easier it is to drive on.