What happened
The pilot reported that he overflew the runway in an effort to determine the depth of the snow covering the surface. During this low pass, the pilot observed tire tracks adjacent to the runway and estimated the snow depth to be approximately two inches. Based on this visual assessment, the pilot initiated an approach for a landing.
During the landing roll, the nose wheel dug into the snow, causing the airplane to nosed over. Subsequent examination revealed that the snow was actually five inches deep with a crusty top layer, significantly deeper than initially perceived.
The investigation
It was determined that the airport/facility directory stated that the airport was closed at the time of the accident.