CHICAGO -- National Weather Service officials expect “blistering” heat over the next two days to hit the heart of the country, from Chicago to the Gulf Coast states, where the heat index, which measures what the temperature feels like, could approach 120 degrees. Wednesday marks the first excessive heat warning for the year in Chicago, said Kevin Birk, a meteorologist at the National Weather Service in Romeoville. He said the weather service issues the warning when the heat index climbs above 110 degrees in the afternoon, with little relief at night. The heat index measures relative humidity a...