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. Here’s what to know. 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 at a time, trap heat at the surface and help to amplify it, said Zachary Labe, climate scientist at Climate Central, an independent collective of scientists. How has heat affected the world this year? Heat impacted various regions of the world early in 2026. The continental United States registered its most abnormally hot month in 132 years of records in March, with record-shattering extremes first in the Southwest and then across the rest of the nation. Heat scorched the French Open and scorched parts of India in May. Extreme heat has since been top of mind for the World Cup across the U.S., Canada and Mexico. Starting mid-June, Europe has baked under unseasonable highs of around 40 degrees Celsius (104 Fahrenheit) in many places due to a heat dome. Now, much of the Eastern U.S. is expected to be slammed by a long heat wave in the coming days, and already, much of the Southwest is experiencing temperatures around 100 degrees Fahrenh