A heatwave with record-breaking temperatures upended Independence Day celebrations across the central and eastern United States on Friday, forcing the cancellation of the National Independence Day Parade in Washington and dozens of other events. The parade, a centrepiece of the nation’s 250th anniversary commemorations, was called off late Friday due to safety concerns as heat index values were projected to reach 46°C (115°F), according to organisers.

Across the Eastern Seaboard, officials cancelled or postponed parades, concerts and fireworks displays. Philadelphia’s Salute to Independence Parade was scrapped after temperatures tied a 1901 record of 39.4°C (103°F) on Thursday. In New Jersey, Haddon Township cancelled its annual parade, while Watertown in upstate New York called off its concert and fireworks. Boston delayed entry to a riverside fireworks celebration by four hours. The National Weather Service said more than 185 million people—over half the US population—were under heat alerts, with peak heat indexes forecast to hit 46°C in parts of the country.

The extreme heat strained power grids. PJM, the largest US grid operator, ordered customers in emergency conservation programmes to reduce usage, citing generator outages and surging air-conditioning demand. In New York, Con Edison reported roughly 17,000 customers without power as of late Friday afternoon. Medical sources in Washington said emergency services treated multiple people for heat-related illnesses near the National Mall, with at least eleven transported to hospital.

The Great American State Fair on the National Mall, a signature event of President Donald Trump’s 250th anniversary programme, was temporarily closed on Friday afternoon as temperatures reached 38°C (101°F). Organisers said they expected to reopen with cooling measures, but local media later reported it had reopened; the exact status remained unclear. Trump’s outdoor speech on Saturday was still scheduled, with the president joking he would give “a really long speech just to show I can do anything.” The heatwave, driven by a high-pressure “heat dome” that moved east from the Midwest, also threatened World Cup matches, with some stadiums lacking air conditioning. Officials said the heatwave would persist through Saturday and urged the public to stay hydrated and seek shade.