What is a heat dome? Here’s why the U.S. is so hot right now
A heat dome is behind the dangerously hot and humid conditions that are currently choking much of the eastern United States. This stubborn weather pattern triggered heat alerts for around 150 million people on Wednesday alone. Temperatures soared above 95°F (35°C) across the Ohio Valley and along the East Coast, with the National Weather Service warning that “extremely dangerous heat” will persist through Thursday.
But what exactly is a heat dome, and why does it bring such oppressive conditions?
A heat dome forms when a strong, persistent area of high pressure settles over land and traps hot air beneath it—like a lid on a pot. This lid prevents hot air from rising and escaping, leading to intensifying heat and stifling humidity at ground level.
The phenomenon is closely linked to the jet stream, a high-altitude ribbon of fast-moving air that flows from west to east in the Northern Hemisphere. The jet stream is powered by temperature contrasts between cold polar air to the north and warmer tropical air to the south. As it meanders across the globe, it can dip or bulge, creating troughs and ridges that often trigger unusual or extreme weather.
Some of these bends allow cold air to plunge southward, while others push hot air masses over land, driving up temperature and humidity. The result is a dangerous combination of searing heat and thick, moisture-laden air that can strain the body and increase health risks.
While the eastern half of the United States is baking under one heat dome, another is driving temperatures up across western Europe. Parts of France this week are forecast to hit triple-digit highs, nearing 100°F (38°C).
Heat domes can linger for days or even weeks, fueling prolonged heat waves that have the potential to become deadly. Heat-related illness and death can affect people of all ages, but children, older adults, and those with pre-existing health conditions are especially vulnerable during extreme heat events.
Climate change is also making these events more frequent, intense, and longer-lasting. According to the National Oceanic and Atmospheric Administration, the 10 hottest years on record since 1850 have all occurred within the past decade.
Some relief is expected later this week across the Midwest and up and down the East Coast, but high temperatures and humidity are likely to persist in the coming days.
