An intense heat wave is expected to blanket much of the central and eastern United States this week as a “heat dome” takes hold in the region, bringing days of muggy, hot and humid days ahead of the Fourth of July weekend and FIFA World Cup games in several U.S. cities.
Forecasters said it could feel as hot as 46 degrees Celsius (115 degrees Fahrenheit) in some places. The National Weather Service (NWS) said the situation was “dangerous” as dozens of temperature records could be broken. More than 60 million people are currently under heat warnings.
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This week’s forecast centers around a weather phenomenon known as the heat dome. What is it? Why does it make heatwaves even more intense and unbearable?
What is a heat dome?
Heat domes are large areas of high pressure that form when warm air flows north, acting like a lid over the atmosphere and trapping hot air near the ground.
As the air sinks, it becomes compressed and warms even more. At the same time, the pressure system prevents cold air and storms from entering, allowing heat to accumulate at the surface and remain trapped there. With fewer clouds and less wind, the sun hits the ground more directly, creating a heat feedback loop.
Heat domes are associated with prolonged heat waves that can last several days.
How long will it last?
A heat dome is already building and is expected to intensify over the next few days, spreading from the central United States toward the East Coast and continuing dangerous heat for several days into early July.
The hottest conditions are expected on Thursday and Friday, according to the NWS, and are expected to continue into the 250th anniversary of the Fourth of July weekend, and forecasters say extreme heat is likely to continue in parts of the Great Plains, Southeast and mid-Atlantic into next weekend.
What will the highest temperature be?
Expect daytime temperatures in the high 30s C (low 100s F) in many locations, but the humidity will make it feel even hotter. In some areas of the central and eastern United States, the heat index, which is the heat index when humidity is taken into account, can reach 40 to 46 degrees Celsius (100 to 115 degrees Fahrenheit).
“This is heat that affects everyone,” said NWS meteorologist Brian Putnam. “This isn’t just the elderly or young children or people who spend a lot of time outdoors and are pushing themselves a little harder than normal. This heat can affect everyone, especially those who are outdoors heading into the holiday season.”
There will be less relief at night, with temperatures expected to remain in the 20s Celsius (70s Fahrenheit) overnight, creating a potentially miserable sleeping environment for those without air conditioning and making it difficult to cool down.
“Even after the sun goes down, it’s still going to be very hot,” said AccuWeather senior meteorologist Alan Reppert. “We’re in a pattern where it gets hotter for a good part of the afternoon and even into the evening.”
Which parts of the United States will be hit the hardest?
The most dangerous conditions are expected in a wide corridor stretching from the Great Lakes to the East Coast, where some cities could experience their hottest days ever. New York City, Philadelphia, Washington, Baltimore, Chicago, Indianapolis, Detroit, and St. Louis are all expected to be affected, and temperatures will also rise further south in Dallas, Little Rock, and Memphis.
Some of these cities also host FIFA World Cup events. In Philadelphia, organizers have already changed the timing of the fan festival to start later in the day.
Cities across the U.S. are taking emergency measures as temperatures rise.
The city of Chicago announced it would open cooling centers and send city workers to check on vulnerable residents.
In New York City, Mayor Zoran Mamdani’s office announced an “unprecedented” response to the heat, including hydration vans and pop-up cooling stations equipped with misting fans and cooling towels.
Temperatures in Washington, D.C., are expected to exceed 38 degrees Celsius (100 degrees Celsius) from Thursday into Saturday, coinciding with Fourth of July celebrations that organizers say will be the largest fireworks display ever held on the National Mall.
What are some ways to stay cool?
The NWS says people should stay hydrated, avoid strenuous outdoor activities during the hottest parts of the day, and use air conditioning and cooling facilities whenever possible. If you spend time outdoors, wear loose, light clothing and stay near a shady area.
Experts say one of the biggest risks of a prolonged heatwave is that the body doesn’t have time to cool down overnight, so the effects of the heat can accumulate day by day. It also recommends drinking water before you’re thirsty and avoiding alcohol, which can increase the risk of dehydration.
“If you notice that you’re not sweating even though it’s hot, or you’re starting to feel a little dizzy, that’s a sign that you really need to take a break, go indoors, find some cool air, and drink plenty of water,” says Jeff Cornish, assistant chief video meteorologist at weather forecasting company AccuWeather. “And if you start having really serious symptoms, you need to see a doctor right away.”
