Sweltering heat dome threatens US holiday plans, power grids

Naureen S. Malik and Joe Wertz, Bloomberg News on Jul 3, 2026

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A searing heat dome will push electricity demand across the eastern U.S. toward record levels over the July 4 holiday, testing power grids as air conditioners run full tilt on a busy World Cup weekend.

The dangerous heat wave is forecast to bring triple-digit temperatures to many U.S. cities, including New York. More than 180 million people spanning Kansas to Maine were under extreme heat warnings or heat advisories on Friday, according to the U.S. Weather Prediction Center. Heat advisories stretch from Michigan as far south as Alabama.

“Today looks to be quite oppressive,” Frank Pereira, a senior branch forecaster at the center, said by telephone, noting “well-above-normal temperatures from the Plains and Midwest to the Mid-Atlantic and Northeast.”

Hundreds of temperature records — for daytime highs and warm overnight lows — are likely to be tested through the weekend, according to the U.S. Weather Prediction Center. That’s straining power systems across the region, with more than 76,000 customers without electricity a little before noon ET, data from PowerOutage.com show.

The country’s largest grid serving nearly a fifth of Americans from Washington to Chicago is operating in an emergency — at the lowest of three levels — for the third consecutive day. PJM Interconnection LLC ordered all power plants to be available at maximum levels for the entire day as it faces a capacity emergency.

“PJM is not in an emergency for any other reasons really than power outages,” said Adam Sinn, chief executive officer of hedge fund Aspire Commodities. There were about 9.5 gigawatts of generation outages in the mid-Atlantic region, including data centers concentrated in northern Virginia, compared to prior forecasts that had shown less than a third of that, he said.

While electricity usage is set to ease slightly Friday amid holiday travel, cooling demand may spike again as the hot and humid conditions persist. The risk of failures at power plants or other critical equipment rises with high sustained demand.

The sprawling heat dome adds another major complication: grids that typically rely on each other for spare supplies may limit supplies to neighbors to keep their systems stable.

Temperatures in Central Park spiked to 100 degrees Fahrenheit (38 degrees Celsius) on Thursday — making it the hottest day in the city since 2012. Records were set from Caribou, Maine, to Chattanooga, Tennessee, including in Boston, Baltimore’s Inner Harbor, and Washington’s Reagan National Airport, Pereira said. Oppressive temperatures and humidity are forecast across the city and the eastern half of the U.S. through the weekend.

Consolidated Edison Co., which runs New York City’s electric utility, has asked about 133,000 customers in Northern Brooklyn to conserve energy to allow crew to repair equipment. Voltage was throttled back by 8% to allow them to do it safely, limiting power flows. Those households were asked to not use washers, dryers and microwaves, and to use only one air conditioner if they have two, the utility said in a statement.

In northern Illinois, Exelon Corp.’s ComEd utility restored power to more than 45,000 customers after severe storms Thursday night and is working to on repairs to bring back the remaining 10,400 customers, according to a statement.

Daytime highs in Philadelphia are forecast to top 99 F (37 C) on Friday, according to weather models from the U.S. and the European Centre for Medium-Range Weather Forecasts. The city will host the World Cup match between France and Paraguay on Saturday.

Similar temperatures are also set for Washington and Newark. Brazil will take on Norway at New Jersey’s Metlife Stadium on Sunday.

PJM, which manages the grid serving the Washington and northern Virginia’s data center alley, expects demand to climb to about 160.9 gigawatts at about 5 p.m., down from Thursday’s high of about 162.4 gigawatts. The grid operator previously forecast that usage could topple the 2006 record of about 165.6 gigawatts, but demand came in lower amid emergency actions.

The priciest hour for wholesale electricity prices across the PJM grid will be from 7 p.m. at $739.04 a megawatt-hour, down 40% from Thursday’s high of $1,219.91.

Thus far, “the Fourth of July heat wave had fewer fireworks than expected” in the power markets, said Sean Kelly, CEO of AI-driven power-demand forecaster Amperon, based in Houston. “Lots of record temps, but flexible load seemed to have shed 4-6 GW, showing that these new data centers are being good neighbors.”

Even though demand on the PJM grid fell shy of the record, it was still about 6 gigawatts higher than the anticipated summer peak of 156.4 gigawatts in the grid operator’s seasonal outlook, according to Kelly. “And the historically hottest part of the summer is just getting started.”

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(With assistance from Brian K. Sullivan.)