This study aims to understand the influence of the Lake Michigan Marine Boundary Layer on the September 21, 2010 thunderstorm squall line. First, the synoptic weather pattern, regional surface conditions, and atmospheric stability were described. Surface temperature, wind and dewpoint temperatures were evaluated to determine how conditions were affected by the lake and the passing of the MCS. Next, the squall line was examined throughout its evolution from the development through the crossing of Lake Michigan. Upwind and special downwind soundings taken by the University of Illinois were analyzed for stability and wind shear. The storm evolution can then be related to how the marine boundary layer influences convection. Once these interactions are better understood, they can be applied to other events and improve forecasting skills.