An excessive heat warning remains in effect until 7 PM CDT Friday. Nighttime heat indices only fall to the upper 70s to middle 80s with the warmest readings in urban areas. * Impacts... this prolonged heat wave is expected to last a week... and will have potentially life-threatening impacts. During the early to mid afternoon... the dangerously high heat and humidity... combined with full sunshine and light winds... will lead to a high potential for heat exhaustion or heat stroke for persons without adequate cooling and shelter. Longer- term cumulative effects are also expected for those most susceptible to the heat... especially the elderly. In addition... higher concentrations of ozone will further increase the potential for respiratory illness for some people.