WASHINGTON — A powerful heat dome pushed more than half of the United States into dangerous and, in many places, record-setting heat on Saturday, prompting officials to issue widespread health warnings, disrupt Independence Day events and urge residents to limit outdoor activity during the country's 250th anniversary celebrations.
The U.S. National Weather Service said excessive heat warnings and heat advisories covered much of the Midwest, Mid-Atlantic and Northeast, with more than 185 million people under heat alerts as temperatures climbed into the upper 90s and low 100s Fahrenheit (mid-30s to around 40 degrees Celsius). Combined with high humidity, heat index values reached as high as 115 F (46 C) in some locations.
Forecasters said the prolonged spell of high pressure, commonly known as a heat dome, trapped hot air over the eastern half of the country, producing unusually warm daytime temperatures and overnight lows that offered little relief. The National Weather Service warned that the combination of persistent heat and humidity significantly increased the risk of heat-related illness, particularly for older adults, children, outdoor workers and people without access to air conditioning.
The extreme conditions disrupted Fourth of July events across several cities. In Washington, D.C., officials canceled the Independence Day parade because of excessive heat, while organizers temporarily suspended activities at the Great American State Fair after dozens of people required medical attention for heat-related illnesses. Elsewhere, parades, fireworks displays and outdoor celebrations were postponed or canceled as local authorities urged residents to seek cooling centers and remain hydrated.
The heat also strained energy infrastructure. PJM Interconnection, the operator of the nation's largest electric grid, called on consumers to conserve electricity as air-conditioning demand surged and some generating units experienced outages. In New York City, utility Con Edison reported thousands of customers without power during the period of peak demand.
Meteorologists said numerous daily temperature records were expected to fall across the eastern United States over the holiday weekend, with exceptionally warm nighttime temperatures reducing opportunities for recovery from daytime heat. Forecasts indicated the hottest conditions would persist through the weekend before gradually easing in some northeastern areas.
Officials continued to advise people to avoid strenuous outdoor activity during the hottest parts of the day, drink plenty of water, check on vulnerable neighbors and seek immediate medical care for signs of heat stroke as the dangerous weather pattern remained in place.
