In a written statement, the pilot reported that while taxiing the airplane to the active runway, he observed thunderstorms approaching from a distance. He opted to return and scrub the flight. After reaching the ramp area he spoke with a friend about the weather and then decided to attempt to depart again. As he was taxiing to the active runway again the precipitation became heavy and hailstones began to fall. He again decided to not depart and requested to taxi back. After being cleared, he continued to the ramp area and encountered a strong wind. The airplane began to rock and he reacted by steering the nose into the wind in an attempt to gain control. The wind continued to shake the airplane, tipping the right wing downward on the taxiway surface. The hail became so severe that the pilot could not see out the windshield, nor could he control the airplane. The airplane came to rest inverted approximately 65 feet off the taxiway. The closest official weather observation station was at the airport. A special Meteorological Terminal Aviation Routine Weather Report (METAR) issued 5 minutes after the accident indicated winds at 11 knots, gusting to 18 knots with thunderstorms in the vicinity. Another special METAR was issued 11 minutes thereafter indicating winds at 30 knots, gusting to 58 knots with heavy thunderstorm and rain activity. The airplane incurred damage to the wing spar during the accident sequence. The pilot reported no preimpact mechanical malfunctions or failures.