CHICAGO, June 14 (Xinhua) -- The Chicago metropolitan area is bracing for a heat wave, as the U.S. National Weather Service issued a heat advisory for the area on Monday.

       Just after 3 p.m. Tuesday local time, the temperature at Midway reached 37.8 degrees Celsius for the first time since July 2012. At noon, O'Hare had a temperature of 34 degrees Celsius, with a 39-degree-Celsius heat index, Chicago Tribune quoted tweets of the weather service.

       The heat index, which shows how the heat is felt by the body, is expected to top 40.5 degrees Celsius in the area for two consecutive days on Tuesday and Wednesday. But it will feel even hotter, as high levels of humidity will make the heat index warmer, the National Weather Service hydrologist Scott Lincoln said.

       An excessive heat warning will be in effect until 8 p.m. Wednesday.

       Worse is that storms swept through the Chicago metropolitan area Monday evening, leaving 125,000 residents in northern Illinois without power.

       Chicago authorities are opening cooling centers and pointing residents to libraries, and even park splash pads.

       "The City of Chicago's cooling areas located at the city's six community service centers will be activated," the city's Office of Emergency Management and Communications said in a statement Monday. The cooling centers will operate from 9 a.m. to 5 p.m.