Examining the Land-Lake-Atmosphere Interactions of the May 5, 2003 Severe Weather Event over Southwest Michigan

In this study, the land-lake-atmosphere interaction of the Great Lakes region in the United States is examined from a case study in early May 2003. During this event, a line of cumulus clouds formed in post cold frontal air several kilometers inland from Lake Michigan over southwest Michigan. These clouds eventually evolved into a line of severe thunderstorms that propagated to the east, resulting in the formation of a tornado over southeast Michigan. This type of convective initiation has been observed by forecasters in the area, and can evolve into a high impact event in terms of public safety and water budget in the region. The combination of a relatively cold lake with convective initiation inland results in a downwind shift in rainfall from these events. This in turn creates a rain shadow parallel to the shore tens of kilometers inland. Depending on where this rainfall initiates, it can have impacts on the agricultural industry near the Lake Michigan shore.

While tempting to classify this case as a simple lake-breeze, the results indicate there to be several other factors involved to create this convective initiation. The interaction between large-scale dynamics and local influences on the environmental thermodynamics by the lake are believed to have played an important role. The thermodynamic and dynamic structure of this system is explored through a series of high-resolution (2km horizontal grid scale) Weather Research and Forecasting Model (WRF) simulations. Lake surface temperatures are altered in subsequent simulations to test the sensitivity of the placement and strength of initiation to the lake's thermodynamic environment.