Severe thunderstorms developed over parts of Illinois, Indiana, Kentucky and Tennesee during the afternoon and evening of 28 March 1997, producing 18 tornadoes and several reports up large hail (up to baseball-size) and strong winds (up to 88mph). The approach of colder and drier air in the mid-troposphere coupled with increasing low-level moisture along and ahead of an approaching cold front led to moderate to strong convective instability over much of the Ohio and Tennessee valleys. GOES-8 sounder-derived lifted indices less than -7 began to expand northward into southeast Missouri and southern Illinois a few hours before convection began to form over that region.