The influence of the marine boundary layer on convection is still being investigated due to the challenge in forecasting the storm intensity changes over lakes. The Great Lakes region is an area of the United States that encounters many Mesoscale Convective Systems (MCS) and provides difficulties in predicting storm evolution. According to a study by Graham et al., MCS crossing Lake Michigan usually maintained their intensity under stable conditions and weakened under unstable conditions with small lake and over-lake air temperature differences. According to another study by Workoff et al., the evolution depends on the type of storm, time over the lake, wind shear, and stability.

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.