A level 4-of-4 extreme heat risk — signaling rare, long-lasting heat with little overnight relief — is forecast early next week for parts of those regions, including St. Louis, Chicago, New , Maps show where extreme humidity and 90- or 100-degree temperatures will affect around 255 million people across the United States. High heat and humidity will intersect over the Plains, with , A heat wave is forecast across the eastern United States, and it's expected to bring severe storms and several days of record high temperatures at the start of the weekend and into next week , The average high for this time of year in Duluth is closer to 71 degrees. extreme" heat is forecast to begin moving into the region on Sunday. greatly increase the risk of heat exhaustion , Just in time for the start of summer on June 20, a heat wave is expected to scorch a large section of the United States, forecasters said. daily high temperatures are forecast to be well into , .