* WHAT...Heat index values up to 100-103 degrees. * WHERE...Portions of central and south central Iowa, including the Des Moines metro. * WHEN...Until 7 PM CDT Wednesday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses. * ADDITIONAL DETAILS...While heat index values may not reach 105 degrees each day, the combination of the longevity of the heat and little or limited relief during the overnight periods with warm lows have prompted the multi-day Heat Advisory.