* WHAT...Heat index values of 100 to 108 expected. * WHERE...Portions of southern Illinois, southwest Indiana, western Kentucky, and southeast Missouri. * WHEN...From noon CDT /1 PM EDT/ today to 8 PM CDT /9 PM EDT/ Wednesday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses. * ADDITIONAL DETAILS...Peak heat index values will be closer to 100 degrees today. Dangerous heat and humidity may also extend into Thursday depending on the timing of a cold front.