On April 7, 1998, approximately 1155 mountain daylight time, a Cessna P206B, N4728F, was substantially damaged when it collided with terrain while maneuvering to reverse direction 19 miles southeast of Riverton, Wyoming. The commercial pilot was seriously injured, one passenger sustained minor injuries, and two passengers were not injured. Instrument meteorological conditions prevailed, and no flight plan was filed for the personal flight being conducted under Title 14 CFR Part 91. The flight originated at Rock Springs, Wyoming, approximately 30 minutes prior to the accident. The following is based on the accident report submitted by the pilot. He and his passengers had flown from Utah and landed at Rock Springs, Wyoming. He obtained a weather briefing and was told that Gillette, Wyoming, and Billings, Montana, were reporting instrument meteorological conditions, and no weather was available for Riverton, Wyoming. Since visual meteorological conditions prevailed at Rock Springs, he made the decision to proceed and assess the weather en route. While in cruise flight, the aircraft penetrated a line of light drizzle and snow showers. The pilot noticed "what appeared to be a limitation to forward visibility" ahead of him, but due to the flat light (sic) conditions, he underestimated his distance from the terrain. As a result, he did not slow the airplane down from cruise speed in enough time, and subsequently lost visual references for approximately 20 to 30 seconds. After he had regained visual conditions, he attempted to slow the aircraft down and turn 180 degrees, following a return course on his Global Positioning System. As he established himself on the course, he noticed a hill in front of their path and began to turn away from it to the left. In an attempt to shorten his turn, he added flaps. The left lower wing struck a rise in the terrain, and the airplane impacted the ground. In his accident report, the pilot said that there was 1 mile visibility, a broken ceiling between 500 to 1,000 feet, and moderate snow showers. The left wing was torn off, and there was damage to the engine, the right wing, the nacelle, landing gear, and fuselage.