The pilot reported that, as he neared his destination, he became distracted by worsening weather conditions and forgot to switch fuel tanks. As a result, the fuel was depleted from the right fuel tank, and the airplane suffered a total loss of engine power. While attempting to restart the engine, the pilot intended to the move the selector to the left tank, but inadvertently moved the fuel selector from the right tank to the off position instead. Unable to restart the engine, the pilot selected a field to perform a forced landing. Prior to touchdown, the pilot realized the fuel was selected off and moved the fuel selector to the left tank; however, before power could be restored, the airplane impacted terrain, resulting in substantial damage to the wings, fuselage, and empennage. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.