The pilot of the tailwheel-equipped airplane reported that, during landing, as the tail came down, a "sizable gust weathervaned" the airplane to the left. He added that, he "made aggressive inputs to correct the direction" but was unsuccessful. He further added that, once the airplane veered off the runway and into the grass, he could feel the mains begin to sink into the soft ground. Subsequently, the airplane nosed over. The airplane sustained substantial damage to the right wing lift struts and empennage. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. A review of recorded data from the automated weather observation station located on the airport revealed that, about 16 minutes after the accident, the wind was from 170° at 9 knots. The airplane landed on runway 18.