The Great Lakes are notorious for their downwind influence on cold season weather systems in general and snowfall in particular. Many previous research investigations have described the salient features of the cool season Great Lakes meteorology. Less studied and less appreciated is how the presence of the Great Lakes influences (and is influenced by) warm season weather systems, particularly convective weather phenomena.

The purpose of this talk will be to illustrate how thermal and moisture boundaries, modified and distorted spatially and diurnally by the Great Lakes, can impact transient weather systems crossing the Great Lakes. Examples will be taken from the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) that was conducted from 20 May to 7 July 2003. Two cases are especially noteworthy. The first case was a long-lived mesoscale convective vortex (MCV) that moved from New Mexico to the eastern Great Lakes from 10-13 June 2003. As the MCV approached the eastern Great Lakes it interacted with a coastal thermal boundary, thus acquiring frontal structure that impacted the spatial distribution of precipitation around the MCV. The second case involved squall lines that unexpectedly reintensified as they crossed the cold waters of Lake Michigan on 4 and 7 July 2003. Preliminary analysis suggests that thermal boundaries anchored to the lake shores and differential roughness between water and land may have played a role in squall line reintensification.