Heat in Williamson, Illinois

Heat indices peaked around 105 degrees during the afternoon. A total eclipse of the sun during the afternoon helped to keep temperatures and heat indices from climbing higher. At a music festival near Marion, 15 people had to be treated for heat-related illnesses. The peak heat indices were 107 degrees at Mount Vernon and Cairo, 106 at Carmi and Fairfield, and 105 at Carbondale and Harrisburg. A strong 500 mb ridge over the southeast U.S. and Lower Mississippi Valley resulted in hot and humid weather. Surface high pressure over the central Appalachian Mountains produced a south wind flow of hot and humid air.