Significant ‘Heat Dome’ Builds Across Much of US, NWS Says

About 95 million people are under some form of advisory on Wednesday and Thursday, say federal forecasters.

Published: 7/23/2025, 5:44:18 PM EDT

Significant ‘Heat Dome’ Builds Across Much of US, NWS Says — A map of heat alerts issued by the U.S. National Weather Service, dated July 23, 2025, shows that tens of millions of Americans are currently under some form of heat-related advisory or warning. (U.S. National Weather Service via The Epoch Times)

A massive “heat dome” will bring long-lasting high temperatures across swaths of the United States starting this week, according to federal weather forecasters, who say that more than 80 million people are currently under some form of heat-related advisory as of Wednesday.

“Dangerous heat is expected” across portions of the southern and central United States through the end of this month, the National Weather Service (NWS) said on Wednesday in a message on its website.

The agency further said that more than 95 million Americans, from the Mississippi Valley to the Northeast, are currently under heat-related warnings and advisories Wednesday through Thursday. A website operated by the NWS shows that as of Wednesday afternoon, 88 million people are under some kind of heat alert.

“The remainder of the week features a strengthening heat dome over the Mississippi Valley today that gradually builds east towards the East Coast by week’s end,” the NWS said in a bulletin. “A combination of mid-upper 90s for high temperatures and humid conditions is a recipe for oppressive heat indices that range between 100-115 [Fahrenheit] for many areas along and just east of the Mississippi River,” on Wednesday.

Record temperatures in some areas are also to be expected, according to the NWS, which said that the record heat will come as overnight and morning low temperatures in some places will drop to the mid-to-upper 70s Fahrenheit.

A heat dome is an area of high-pressure air in the atmosphere that gets stuck over a region because atmospheric dynamics around it block it from moving. It works like putting a lid on a boiling pot. The high-pressure system traps hot air below it, which heats up and compresses to form a dome, which then intensifies heat and prevents the formation of clouds, allowing even more radiation from the sun to reach the ground below.

A heat dome results in clear, sunny days and still conditions with little cooling wind.

Data compiled by the NWS shows that excessive heat kills 183 Americans per year on average, outpacing the average number of people killed by floods, tornadoes, hurricanes, and lightning.

Health officials say that people at the most risk of heat stroke or heat exhaustion include infants, younger children, older adults, people with mental health problems, pregnant women, and those with chronic medical conditions such as heart disease, obesity, and poor blood circulation.

Symptoms of heat stroke include a body temperature of 103 degrees or higher; red, hot, dry, or damp skin; a rapid and strong pulse; nausea, confusion; dizziness; headache; or a loss of consciousness, according to the U.S. Centers for Disease Control and Prevention and other health agencies.

People suffering from heat stroke should receive immediate medical attention, and 911 should be called, officials say.

Earlier this month, the National Oceanic and Atmospheric Administration, which oversees NWS, released its U.S. forecast for 2025, suggesting “above” normal temperatures in much of the United States. That includes nearly all of the East Coast, most of the West Coast and Mountain states, and some portions of the upper Midwest, according to a map from the agency.

Reuters contributed to this report.

From The Epoch Times