* WHAT...Heat index values up to 105 expected. Overnight low temperatures between 75 and 80 offer limited relief. * WHERE...Portions of southwest Iowa and east central and southeast Nebraska. * WHEN...From 1 PM Wednesday to 7 PM CDT Thursday. * IMPACTS...Hot temperatures and high humidity may cause heat illnesses. Several days of excessive heat will add to cumulative heat stress. * ADDITIONAL DETAILS...The heat advisory may be extended or expanded as the prolonged heatwave continues.