Here are the states that have specific snow/ice removal laws: Alaska, Connecticut, Georgia, Massachusetts, Michigan, New Hampshire, New Jersey, Pennsylvania, Rhode Island, Tennessee, Wisconsin.
Minnesota has no snow/ice removal law like Michigan, for example, but a Minnesota state trooper is quoted on many websites saying snow/ice could be 'considered' a load. I think it's a stretch to say snow is a load that needs to be covered, tied down, secured, etc. (Being a city cop, I've never been too impressed with state troopers, they tend to make stuff up from my experience).