On 4 July, the United States celebrated the 250th anniversary of its independence during a serious heatwave. Many cities planned big parades, concerts, and fireworks, but extremely high temperatures changed these plans. In Washington, DC, the temperature reached about 38°C, and the heat index was expected to rise to 46°C. The Great American State Fair was closed for a time, and the main Independence Day parade was cancelled.

This happened because a heat dome formed over the central and eastern parts of the country. A heat dome traps hot air close to the ground, which causes very high temperatures and keeps cities hot even at night.

Because of the heat, outdoor activities were cancelled or changed in several cities. Officials told people to drink water, stay in the shade, and watch for signs of heat illness.