What happened
The takeoff of the glider and the tow plane proceeded normally, with the glider becoming airborne before reaching midfield. The pilots had a prior agreement that if the glider was airborne by the midfield point, the glider pilot would initiate the release.
During the climb, the tow plane pilot encountered a wind gust or wind shear that initially lifted the aircraft and then caused it to settle toward the ground. Sensing that the aircraft was not accelerating or gaining altitude as expected, the tow plane pilot released the tow line.
The glider pilot continued to follow the tow plane to maintain the proper position. As the tow plane began its climb out, the glider pilot realized the release had occurred and observed his airspeed deteriorating. The right wing of the glider began to stall and drop. In an attempt to land in an empty parking lot, the right wing struck the railing of an observation deck. There were no injuries reported.
The tow plane pilot stated he did not warn the glider pilot about the release because he assumed the glider pilot would see and feel the disconnection, and he did not want to distract the other pilot from flying the aircraft.