FILE - Workers in hot weather work at a Radio Frequency Environment area in Riverwoods, Ill., Monday, June 17, 2024. While a heat wave brings the hottest temperatures so far this year to the Midwest and Northeast, forecasters also are discussing heat domes. What's the difference? A heat dome forms when high pressure in the upper atmosphere causes the air below it to sink, heat up and expand. (AP Photo/Nam Y. Huh, File)