* WHAT...Dangerously hot conditions with heat index values from 98 to 105. * WHERE...Portions of central Upper and western Upper Michigan. * WHEN...Until 10 PM EDT /9 PM CDT/ Tuesday. * IMPACTS...Heat related illnesses increase significantly during extreme heat and high humidity events. * ADDITIONAL DETAILS...Overnight low temperatures will range from 70 to 75 degrees, limiting recovery from heat.