* WHAT...Peak heat indices of 100 to 105 degrees expected Tuesday and Wednesday afternoons. * WHERE...Portions of northern and central Illinois near and south of I-80, as well as all of northwest Indiana. * WHEN...For the first Heat Advisory, from noon CDT to 9 PM CDT Tuesday. For the second Heat Advisory, from noon CDT to 9 PM CDT Wednesday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses.