Incident Sequence
The pilot of glider N686U reported that he was established in a weak thermal at an altitude of approximately 2,500 feet above ground level (AGL) when he observed two other gliders. One was at approximately the same altitude as his aircraft, and one was below. The glider at the same altitude passed very close to but underneath his glider. The pilot stated that he momentarily lost sight of the glider before seeing it turn and continue in the thermal; however, due to his glider's attitude, he was unable to maintain visual contact with the other glider. Subsequently, N686U was struck from the right rear by glider N40MS. Both pilots then lost control of their gliders, which descended to ground impact.
Aircraft
Two gliders were involved: N686U and N40MS. No further details about the aircraft were provided in the source.
Aftermath
Both gliders descended to ground impact following the collision. The source did not specify injuries, damage, or any further events.