America’s getting a heat dome for July 4th — it won’t kill you at 2pm but might at 2am

These unbearably hot and humid summer months that put millions of people across the globe at risk are typically made possible by phenomena known as heat domes.

Heat domes can make already-high temperatures even more extreme and prolonged, and they are worsening in severity and becoming more frequent as the planet warms.

What makes up a heat dome, and what does it do?

Heat domes are essentially high-pressure systems hovering above a region that trap heat and humidity, experts say.

They result from the northward flow of warm air. That system sends air sinking, pressure increasing and temperatures rising.

“The concept of a heat dome really means that the air in this region is so warm, and we know that warm air expands,” said Jennifer Francis, a climate scientist at the Woodwell Climate Research Center. “It basically means that the layers of the atmosphere are bulging upward as well.”

Simply put, heat domes cause heat waves. They’re associated with very dry, sunny conditions that last for multiple days........

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