This forecast sounding for Dayton, OH shows that the strength of the winds just off the ground were in excess of 50 kt (58 mph).  Not only were these winds able to mix to the ground inside thunderstorm downdrafts, but the very strong low-level wind shear that these winds created favored bowing structures and enhanced thunderstorm winds.  This strong wind shear helped to compensate for the lack of instability (CAPE only 400 J/kg).