Dangerous heat dome to blanket much of the US in coming days

Summer doesn’t officially start until Friday, June 20, but the heat has already arrived — and it’s only going to get worse. Starting Thursday, June 19, the first of two rounds of extreme heat is expected to roast the eastern U.S., with a brutal heat dome building through the weekend and into next week.

More than 15 million people — from Washington, D.C. to Florida — are under a major heat risk.

Heat alerts issued

The National Weather Service has issued extreme heat watches and heat advisories for parts of the central U.S. These alerts represent the highest level of warning issued by the NWS for excessive heat.

Forecasters say the most dangerous conditions will hit the Midwest, including wide stretches of Nebraska, Illinois, Wisconsin and Iowa.

A massive dome of high pressure, often referred to as a “heat dome,” will slowly make its way across the U.S. throughout next week. The heat wave is expected to bring the highest temperatures of the year so far, with AccuWeather meteorologists forecasting some areas to reach triple digits.

When and where will the heat peak?

The heat is expected to hit the country in waves. Forecasters predict the heat will hit the following regions:

• Plains: Thursday, June 19, through Sunday, June 22.
• Mississippi Valley: Friday, June 20, through Sunday in the upper Mississippi Valley. It could last much of next week in the mid-Mississippi Valley.
• Midwest: Saturday, June 21, through next week. Expected to cool down Tuesday, June 24, in the northern Great Lakes, longer in the Ohio Valley.
• Northeast: Sunday, with some relief in New England and the eastern Great Lakes by Wednesday, June 25.

What is a heat dome?

A heat dome occurs when a large area of high pressure in the upper atmosphere traps heat and humidity. This system blocks cloud formation, allowing the sun’s radiation to bake the surface, which dramatically drives up temperatures.

Heat is the deadliest form of extreme weather in the U.S., contributing to more than 800 deaths per year on average since 1999, according to a 2023 study.

This upcoming stretch of heat and humidity will linger well into the evenings for several days, posing serious risks to those without access to air conditioning. This can be especially rough in urban areas, where the “heat island effect” can push temperatures even higher than in surrounding rural regions.

The NWS recommends minimizing direct sun exposure, wearing loose and light-colored clothing, staying hydrated and spending time in air-conditioned spaces.