Postal Worker Rey Marquez, cools himself off from working under the blazing sun along his route in Joliet, IL on Thursday July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Bill Curwick, an operator with the Crest Hill Public Works Department, cuts down a tree under the blazing sun along Leness Lane in Crest Hill, IL on Thursday, July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Postal Worker Rey Marquez, cools himself off from working under the blazing sun along his route in Joliet, IL on Thursday July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Richard Castro, a meteorologist with the National Weather Service, Chicago, takes a photo of the 105-degree reading from a sensor on Northerly Island, at their forecast office in Romeoville, IL on Thursday, July 6, 2012. 102 degrees, the official high temperature for the day, was met at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Bill Curwick, an operator with the Crest Hill Public Works Department, wipes his face after he worked on a tree under the blazing sun along Leness Lane in Crest Hill, IL on Thursday, July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Bill Curwick, an operator with the Crest Hill Public Works Department, works on a tree under the blazing sun along Leness Lane in Crest Hill, IL on Thursday, July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Jim Allsopp, a meteorologist with the National Weather Service, Chicago, looks at a display of the 103-degree reading from a sensor at O'Hare, while working at their forecast office in Romeoville, IL on Thursday, July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .

Postal Worker Rey Marquez, cools himself off from working under the blazing sun along his route in Joliet, IL on Thursday July 6, 2012. 103 degrees, the new official high temperature for the day, was set at O'Hare, which is the official climate site for the city of Chicago. | Matt Marton~Sun-Times Media .