A snow roller is an odd meteorological phenomenon in which cylindrical snowballs are formed naturally as chunks of snow roll down hill or are blown along the ground by wind, picking up further snow along the way, in much the same way that the large snowballs used in snowmen are made. Also known as "snow bales," "wind snowballs," or "snow donuts," snow rollers are the cold weather equivalent of tumbleweeds. They form when wind pushes wet snow across the ground. If the wind is strong enough and almost parallel to the ground the gathered snow will sometimes form a hollow cylinder. The size varies depending on the meteorological factors. The first one I ever saw was just over two feet in diameter. The roller in the post is a modest 18 inches and is the first one I've seen in about 8 years.