An intense and prolonged heat wave could bring record temperatures to the central and eastern U.S. ahead of Independence Day celebrations.
Limited time: Save 25% on NBC News subscription
Get exclusive reporting, live Q&As and ad-free reading.
Nearly 142 million people are under National Weather Service heat alerts, with that number likely to grow as heat moves toward the Southeast, Midwest and Northeast.
“The latest guidance continues to strongly agree on a potentially historic heatwave across the eastern third of the country for the end of the week,” the weather service said in a forecast discussion Sunday.
The weather service added that Thursday and Friday could see “the possibility of all-time record highs” in places.
Cities including Chicago; Kansas City and St. Louis, Missouri; Nashville, Tennessee; Savannah, Georgia; Philadelphia; and Boston are under alerts, with daytime highs expected to climb into the 90s and the 100s.
The weather service’s forecast discussion for Kansas City said the stubborn heat could last through the Fourth of July. “We expect to be locked into a hot and dry pattern through at least Thursday, but probably through Saturday,” it said.
As the wave reaches the East midweek, the heat index value could surge past 100 in Philadelphia and Washington, D.C., with Philadelphia feeling as hot as 112 degrees by Thursday.
The weather service office for New York City issued an extreme heat watch for the region that covers Monday through Wednesday. It notes the “feels like” temperature, known as the heat index, is forecast to reach 108 degrees.
Factoring in the humidity, heat index values could reach 105 to 114 degrees in other places under the dome through the week.
Highs across the East and Southeast will generally be 5 to 10 degrees above normal as the wave spreads eastward, with a few records possible in Florida’s Key West, Miami, Orlando and Tampa.
Much of the Southwest was already facing highs of around 100 degrees.
Fire weather conditions, including continued dry air and gusts up to 30 mph, will persist in much of Arizona, eastern Utah, western Colorado, western New Mexico and portions of southern Wyoming, according to the weather service.
Utah, Colorado and other Western states have been subjected to large-scale weekend wildfires, including the 93,607-acre Cottonwood Fire, where 1,200 firefighters and support personnel had achieved zero containment by late Sunday afternoon, according to a joint command update. Along the Utah-Colorado border, three firefighters assigned to two other fires were killed on the job Saturday, federal officials said.
A series of cooler air pulses from the West will push the weekend’s dry Western heat to the east, where it will park over the Tennessee Valley as it expands, federal forecasters said.
Such a high pressure dome pushes air toward earth, heating it as it descends.
A cold front from the Northern Plains — Wyoming, Montana and the Dakotas — could clash with the heat dome to the south, producing thunderstorms in the Mississippi Valley through Monday, the weather service said.
Across the Atlantic, a historic heat wave sweeping Europe has turned deadly. French officials said the country recorded about 1,000 excess deaths during the recent stretch of record-breaking heat.
A study by earth scientists based in the United States, Australia and China published last year found that “global warming is responsible for long-term increases in the frequency and strength of concurrent heat extremes,” according to a summary.
