THE PILOT REPORTED THAT HE ENCOUNTERED A HIGHER THAN NORMAL SINK RATE ON DOWNWIND AND ENDED UP LOWER THAN NORMAL ABEAM THE END OF THE RUNWAY. INSTEAD OF TURNING BASE EARLY, THE PILOT ELECTED TO CONTINUE ON DOWNWIND AND TURN BASE AT THE CUSTOMARY LOCATION. THE PILOT REALIZED HIS PROBLEM ON BASE AND ATTEMPTED TO TIGHTEN THE TURN TO FINAL TO MAKE THE RUNWAY. THE PILOT REPORTED THAT HE CROSS CONTROLLED THE AIRCRAFT WHILE MAKING THE TURN AND THE GLIDER STALLED, THEN SPUN TO THE GROUND.