Searing US heat dome disrupts July 4 events, strains grid

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

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A searing heat dome was set to push electricity demand across the eastern U.S. toward record levels over the July 4 holiday, straining power grids and halting one of the main events in Washington, D.C., for hours.

The dangerous heat wave was forecast to bring triple-digit temperatures to many American cities and the U.S. capital, where the Great American State Fair — a two-week festival of patriotic-themed events — was forced to close for several hours Friday. Activities will resume after 5 p.m., event organizer Freedom 250 said in a social media post.

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 to as far south as Alabama. The heat is hitting ahead of another busy weekend of World Cup football, with air conditioners likely needed to run full tilt.

“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 weather agency. That’s straining power systems across the region, with more than 76,000 customers without electricity a little before noon ET, according to PowerOutage.com data.

Consolidated Edison Co., which runs New York City’s electric utility, has asked almost 170,000 customers in Northern Brooklyn, Queens and certain communities of Westchester County 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.

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, and had a higher level in place for certain regions, including Northern Virginia’s “data center alley.” PJM Interconnection LLC ordered all power plants to be available at maximum levels for the entire day as it faces a capacity emergency.

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, according to Adam Sinn, chief executive officer of hedge fund Aspire Commodities.

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.

“We need to treat grid flexibility as part of everyday operations, not just crisis response,” said Jigar Shah, a former U.S. Department of Energy official.

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 touched 97 degrees Fahrenheit (36 degrees Celsius) on Friday afternoon local time, a day after the city experienced its hottest day since 2012 with the heat hitting 100 F (38 C). Oppressive temperatures and humidity are forecast across the city and the eastern half of the U.S. through the weekend.

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 at Philadelphia’s International Airport hit 104 F (40 C) on Friday, according to the National Weather Service. The city will host the World Cup match between France and Paraguay on Saturday, when temperatures are forecast to reach 104 F. New Jersey has also faced similar scorching weather, though temperatures are expected to drop below 90 F (32 C) Sunday when Brazil takes on Norway at MetLife Stadium.

PJM, which manages the grid serving the Washington area and Northern Virginia’s data center alley, extended a hot weather alert to Sunday.

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, chief executive officer of AI-driven power demand forecaster Amperon, based in Houston, though “the historically hottest part of the summer is just getting started.”

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(With assistance from Brian K. Sullivan.)