Somewhat surprisingly, McDonough and Schuyler counties in northwestern Illinois, as well as a few others near Burlington, IA, are listed as already experiencing

Somewhat surprisingly, McDonough and Schuyler counties in northwestern Illinois, as well as a few others near Burlington, IA, are listed as already experiencing 125 F (52 C) heat-index days. I would not have guessed that a city in Iowa has more oppressive heat waves than nearly all of the South. I'm still not sure why the (unmeasurable) heat index is preferred over the (measurable) wet-bulb temperature, aside from using bigger numbers that sound more intimidating.