The pilot reported that he made a normal approach, and on short final a gust of wind forced the airplane down to the ground. The airplane went into soft sand and nosed over. The pilot's passenger reported that prior to reaching the airport for landing, he felt some light turbulence. As the airplane was nearing touchdown he felt turbulence again, and heard the pilot say 'oh no.' The passenger reported that it felt as if the airplane was pushed straight down and the airplane impacted the ground short of the runway. A ground witness about 1/4 mile north of the runway watched as the airplane came in to land. As the airplane approached the runway he saw the tail move sideways and then straighten out; he thought that the wind must have caught it. As the airplane continued on the approach, it seemed normal; however, as it got close to the runway, the airplane appeared to drop suddenly as if it was being forced down by a gust of wind.