Actually the problem with snow is specific to Google's approach and is not limited to snow, but to all changes of the environment. They use the 360 degree LIDAR

Actually the problem with snow is specific to Google's approach and is not limited to snow, but to all changes of the environment. They use the 360 degree LIDAR (Velodyne) and drive multiple times over each street in order to create a 3D map which is used for localization after that. Therefore the snow changes the layout of the environment significantly and localization stops working, which in turn makes functions like lane keeping, car detection, traffic light detection etc impossible. This will also happen if the environment changes a lot in another way.