The National Weather Service reported that a heat wave across the United States between June 30 and July 5, 2026, broke or tied over 90 local temperature records. The agency predicted that most of the Lower 48 states would experience a heat dome, causing temperatures 15 to 25 degrees Fahrenheit warmer than normal.

At least 148 daily high-temperature records were set in the eastern U.S. during this period. Washington, D.C., recorded 103 degrees on July 4, 2026, breaking its previous record for the warmest July 4. Philadelphia experienced three consecutive days with temperatures above 101 degrees, a first for the city. Atlantic City, New Jersey, tied its all-time hottest temperature of 106 degrees on July 5, 2026.

In New York City, Mayor Zohran Mamdani activated a heat emergency plan on June 29, 2026, including hundreds of cooling centers and intensified outreach. The National Weather Service issued Extreme Heat warnings and Heat advisories for Idaho's Snake River Plain, beginning at noon on Saturday. Temperatures there were forecast between 100 and 103 degrees, 15 to 20 degrees above average.

Daniel Swain, a climate scientist, said, "This upcoming heat wave does look pretty remarkable." He added, "This is going to be a long duration, widespread and high-intensity heat event that's going to affect millions of people for over a week." Swain also stated, "We know that heat waves are becoming more intense, they're lasting longer, they're covering larger areas than they used to because of human-caused climate change."

Two-thirds of the predicted temperature records involve overnight heat. Nighttime temperatures were not expected to drop below 80 degrees in Fort Lauderdale, Miami, and Tampa, Florida, as well as Galveston, Texas, and Charleston, South Carolina. Meteorologist Bob Henson stated, "Nights can be just as dangerous as days." Henson also noted, "If you don't get heat relief at night, that's going to spill out into your daytime experience and become extremely dangerous." He cautioned, "Heat is not to be played with," describing it as "just as dangerous as a tornado or hurricane that can kill you just as easily, just in a quiet and different way."

Climate Central analysis indicated that heat in a 20,000-square-mile swath from Southern California to northern Minnesota is at least five times more likely due to climate change. This area is home to 24 million people and is affected by the highest level on the Climate Shift Index.