A heat wave will spread north over the central part of the nation and then linger for days. Heat index values could top 115 degrees in parts of Minnesota and the Dakotas. A large swath of heat indices over 105 degrees is predicted from the Gulf Coast to the Canadian Border.
The heat index does a better job of describing how the air feels because it takes into account the added effect of humidity. When the humidity is higher, it’s more difficult to cool off by perspiration so it feels warmer. Heat-related illness becomes more likely for every degree the heat index climbs above 100.