The pilot reported that, during the landing roll, the tailwheel-equipped airplane began to ground loop to the left. He corrected with opposite rudder and aileron and regained control of the airplane, but the airplane started to veer right. The pilot added that, while the airplane was veering right toward the edge of the runway, he assumed the snow on the adjacent field was compacted and would efficiently slow the airplane, so he let the airplane exit the runway to the right; however, the snow was "softer than [he] anticipated," and the airplane nosed over. The airplane sustained substantial damage to the right-wing lift strut. The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation. The airport's automated weather observation system reported that, about the time of the accident, the wind was from 020º at 3 knots. The pilot landed the airplane on runway 20.