Both the glider and tow plane pilots agreed that if the glider was airborne by midfield, the glider pilot would release the tow. Takeoff was normal and the glider was airborne before midfield. The tow plane pilot, however, encountered a wind gust or shear that lifted the tow plane, then caused it to settle to the ground. He sensed he was not accelerating and gaining altitude as he should. He released the tow line. The glider pilot followed the tow plane to maintain proper tow position. As the tow plane climbed out, he realized he had been released and saw his airspeed deteriorating. The right wing began to stall and drop. He attempted to land in an empty parking lot, but the right wing struck the railing of an observation deck. The tow plane pilot said he failed to warn the glider pilot about the tow release because he assumed he would see and feel the release, and he did not want to distract him from flying and glider.