Upon arriving in the vicinity of the airport, the pilot circled the runway twice to determine the wind direction and runway conditions. The runway appeared to look clear, with a few ice patches on the surface, and snow mounds off to the sides. After touching down on the runway, the left landing gear assembly encountered a "low flat" snow patch, and the airplane began to pull to the left. The airplane continued off the side of the runway, and came to rest upright in a snow-covered field.