A massive heat dome is set to descend on the eastern half of the U.S., stretching from the Midwest to the East Coast and putting more than 230 million people in the crosshairs of temperatures above 90F, while millions will experience triple-digit temperatures during the Fourth of July holiday week and into weekend festivities.

The Midwest will be the epicenter of the heat dome early in the week, with metro areas such as St. Louis and Detroit climbing into the mid- to upper 90s.

By Wednesday, the heat shifts eastward, threatening record highs across Washington, Baltimore, Philadelphia and New York City, where temperatures are expected to exceed 100F over multiple days.

Heat wave is inbound, and this one could be among the DC area's most intense.

As we close in on the Wednesday start of an unusually intense and long-lasting blast of extreme heat extending into the Fourth of July weekend, computer models continue to pump out numbers that could… pic.twitter.com/CctcKMJMri

— Capital Weather (@capitalweather) June 29, 2026

Meteorologist Ryan Maue described it as a "mega heat dome" that will produce "record highs (daily) for almost the entire Eastern Seaboard from Maine to South Carolina."

"Fire up the grill, buy plenty of ice 🧊 for your favorite beverages, get your pool floaties in order, and prepare for an extremely hot and humid Independence Day weekend across the Eastern United States with temperatures well over 100°F," Maue wrote in the note.

Bloomberg's two-week forecast for average temperatures across the Washington, D.C., metro area indicates the heat dome will linger until nearly the midpoint of the month. Temperatures are forecast to return to the 30-year mean of around 78F.

This is not global warming - just entering peak summer in North America.

To note, there are mounting El Niño risks (read here & here).