The pilot and witnesses described the airplane touching down with a 20 knot tailwind on the last 25 percent of the approximately 600 feet long, packed snow, landing area. The pilot said that on short final he recognized the tailwind, but because of terrain there was not maneuvering room to attempt a go around. The airplane bounced, and overran the landing area. The pilot said he lost forward visibility in whiteout conditions, and intentionally ground looped the airplane to stop.