Background
The pilot received a weather briefing and filed an IFR flight plan to Boeing Field in Seattle, Washington. He departed Kalispell, Montana, at 1135 Mountain Standard Time.
Flight
Upon reaching the Spokane area, the pilot obtained weather reports for Seattle and decided to turn around and return to Kalispell. However, weather at Kalispell had deteriorated. The pilot was cleared for a contact approach. He then advised Salt Lake Air Route Traffic Control Center that he had a small lake in sight below, was canceling IFR, and was proceeding under visual flight rules.
Accident
Ice fishermen at the lake observed the aircraft making several passes over the water. They then heard the sound of impact. The fishermen described the weather as low ceiling, reduced visibility, snow, and fog.
Post-Accident
Although the pilot could not recall the events leading up to the accident, he surmised that he may have attempted a precautionary landing due to an accumulation of airframe ice. The weather forecast had included flight precautions for moderate rime ice in clouds and precipitation from the freezing level to 14,000 feet.