Sauna-like conditions on Friday are threatening to break records in major Northeast cities during summer’s hottest month after dangerous heat peaked Thursday in the central United States.

A lingering heat dome over the eastern half of the U.S. is putting tens of millions of people in sweltering conditions, with the worst still to come. On July 25 the East Coast is bearing the brunt of the heat,

For people under the sweltering influence of a heat dome, the weather pattern can be excruciatingly tedious to endure, Jackson told Scientific American. “Heat domes are generally slow to form and slow to dissipate,” he said.