U.S. Postal Service employee Earl Sykes, of Hazel Crest, wipes his face with a towel during extreme heat Thursday, June 27, 2012 while walking his delivery route on the 10900 block of Lawndale Avenue in Chicago's Mt. Greenwood community. | Brett Roseman~Sun-Times Media

Liliya Hart takes a quick water break while striping turn lanes for AC Pavement Striping Co. on Roberts Rd. in Palos Hills, Illinois, Thursday, June 28, 2012. | Joseph P. Meier~Sun-Times Media

Mary Casello hands a cold bottle of Gatorade to U.S. Postal Service employee Earl Sykes, of Hazel Crest, as he delivers mail while walking his route in extreme heat on 10900 block of Lawndale Avenue in Chicago's Mt. Greenwood community Thursday, June 27, 2012. | Brett Roseman~Sun-Times Media

Chris Glader-Wendt cools off from the heat in her family pool at their home along Sayre in Oak Lawn, IL on Thursday June 28, 2012. The temperature was just under 100 degrees. | Matt Marton~Sun-Times Media .

Kim Dykema cools off from the heat in the Glader family pool at their home along Sayre in Oak Lawn, IL on Thursday June 28, 2012. The temperature was just under 100 degrees. | Matt Marton~Sun-Times Media .

Dave Robles wipes the sweat from his face while striping turn lanes for AC Pavement Striping Co. on Roberts Rd. in Palos Hills, Illinois, Thursday, June 28, 2012. | Joseph P. Meier~Sun-Times Media

Joe Garcia, a Metra employee, takes adrink of water after checking out a machine at the Metra repair shop along the Metra tracks near Cook street in Oak Lawn, IL on Thursday June 28, 2012. The temperature was just under 100 degrees. | Matt Marton~Sun-Times Media .

Joe Garcia, a Metra employee, works on a machine at the Metra repair shop along the Metra tracks near Cook street in Oak Lawn, IL on Thursday June 28, 2012. The temperature was just under 100 degrees. | Matt Marton~Sun-Times Media .

A sign along 95th Street shows the heat level in Oak Lawn, IL on Thursday June 28, 2012. The temperature was just under 100 degrees. | Matt Marton~Sun-Times Media .