At the moment we can not see foot prints when walking on snowy ground regardless if its snowing or not. Plus when it's snowing heavy or snow storms there should be more obvious snow buildup on the locomotive as well as ice on rails which would have to be chipped off on the action menu otherwise it may cause the player to slip off when moving about the locomotive outside.
Had a night where I was switching when there was sleet coming down. Normally, I have no issues tying a handbrake or going in between cars, but this stuff was slick. If you can moonwalk across the ballast, that's a sign it's too slippery out. During that sleet storm, I was watching the locomotive roll by during a move, and the weight of the loco onto the rail caused the small buildup of sleet to turn immediately to steam.