A persistent heat dome is blanketing the eastern United States, placing tens of millions of people under heat advisories and warnings for the upcoming week.
According to the National Weather Service (NWS), over 35 million people faced a major or extreme risk from heat effects on July 23, a figure centered on the Mississippi River Valley. Forecasts show this number will more than double by July 25, with advisories expected to cover most of the eastern half of the country and affect nearly 90 million people. “Even though it’s midsummer, this is pretty notable,” said Bryan Jackson, a meteorologist at the NWS Weather Prediction Center.
The severe conditions are caused by a heat dome, a slow-moving, high-pressure weather system that traps hot air over a region. Jackson noted that these systems are typically slow to form and dissipate, meaning the current heatwave is expected to last for at least a full week.
A key factor in this event is high humidity, which prevents temperatures from dropping significantly overnight and offers little public respite. “With the high moisture we are seeing, there will actually be quite a few record-high minimum temperatures,” Jackson explained.
The heat dome, currently centered over Memphis, Tennessee, will shift its most intense effects eastward throughout the week. The Midwest has already endured several days of extreme temperatures, worsened by humidity from agriculture. The Ohio River Valley is forecast to face the worst conditions on July 24, followed by the Eastern Seaboard on July 25. The Southeast is projected to see the highest heat risk over the weekend and into next week, with the mid-Atlantic and the Carolinas potentially breaking records for their highest overnight low temperatures.
This event is consistent with the increasing frequency of prolonged heat waves as the climate changes. Recent analysis shows many cities across the eastern U.S. are experiencing more “heat streaks,” defined as periods of three or more consecutive days with exceptionally high temperatures.
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