On Friday, the heat forced the cancellation of a parade in Philadelphia, as well as a number of fireworks displays in the capital, Washington, D.C. Other events were shortened or had their opening hours changed.
The National Weather Service (NWS) is warning of extreme heat throughout the weekend across much of the Midwest, mid-Atlantic and northeastern U.S. Temperatures could reach 104 degrees Fahrenheit (40 degrees Celsius) in parts of the area, and several local heat records could be set.
This may lead to an increased risk of heat-related illness, especially for vulnerable groups, the NWS said.
Major cities such as Saint Louis, Indianapolis, Baltimore, Philadelphia, New York and Boston are covered by the heat warnings.
The heat wave also threatens to overload power grids and could force people to cancel, postpone or otherwise change their plans during one of the most intense travel weeks of the year.
PJM, the largest U.S. electric utility, announced Friday that it is subject to a federal call to reduce electricity consumption in an area covering tens of millions of people.
The state-owned train company Amtrak is canceling some train departures in the northeastern United States because the heat could affect the rails.
