GROUND WITNESSES TO THE ACCIDENT REPORTED THAT THE GLIDER ENTERED THE TRAFFIC PATTERN AT A LOWER THAN NORMAL ALTITUDE AND APPEARED TO BE SLOW. THE GLIDER FLEW A NORMAL LENGTH DOWNWIND LEG AND, WHILE TURNING FROM BASE TO FINAL, STALLED AND DRAGGED ONE WING TIP ON THE GROUND. THE GLIDER THEN CARTWHEELED INTO THE GROUND. THE PILOT REPORTED IN HIS WRITTEN STATEMENT THAT HE ENCOUNTERED STRONG TURBULENCE AND DOWNDRAFTS WHILE ON FINAL APPROACH. THE GLIDER THEN PITCHED NOSE DOWN, ROLLED TO THE LEFT, AND IMPACTED ON THE RUNWAY.