FILE - Wyatt Seymore pours the last drops of liquid from a water bottle into his mouth as he takes a break from unloading a stiflingly hot trailer of fireworks outside Powder Monkey Fireworks ahead of the opening of the stand, Monday, June 17, 2024, in Weldon Spring, Mo. 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/Jeff Roberson, File)