The pilot of the glider reported diverting from his original destination to an alternate airport due to an approaching thunderstorm from the west that he could see. The pilot chose to stay aloft to see which direction the weather was moving. When the thunderstorm started moving east toward the pilot he decided to land. The pilot reported that while he was on final approach for the runway, he was hit by a gust front, the wind shifted and he was blown to the north side of the runway and landed on a dirt road. During the landing roll the glider impacted a fence post and sustained substantial damage to the fuselage and right wing. A review of local weather data showed nearby convective activity capable of producing significant convective gust fronts. The thunderstorm hazard was forecasted by the National Weather Service prior to the flight, which included a special weather statement for the accident area advising that strong outflow gusts up to 50 miles per hour were possible. The pilot reported receiving a weather forecast the morning of the flight that included the possibility for afternoon thunderstorms. The pilot reported no preimpact mechanical failures or malfunctions with the glider that would have precluded normal operation.