Heat Dome Threatens 90+ Temperature Records Across the US
A massive heat dome is poised to bring record-breaking temperatures across large portions of the United States this week, with the National Weather Service predicting that more than 90 temperature records will be tied or broken through Wednesday, July 15. Most of these will be overnight heat records — a particularly dangerous phenomenon that health experts say leaves the body with no time to recover.
According to the Associated Press, temperatures are forecast to remain above 80°F (27°C) overnight in cities including Fort Lauderdale, Miami, Tampa, Galveston, and Charleston. Even northern cities known for frigid winters — such as Fargo, North Dakota; International Falls, Minnesota; and Portland, Maine — will see nighttime temperatures stay above 70°F (21°C).
A Summer of Extreme Heat
This latest heat dome is the second major event of an already brutal summer. The first heat dome settled over the eastern United States and eastern Canada from June 28 to July 5, placing 180 million people under “major” or “extreme” heat risk. During that period, New York City exceeded 100°F (38°C) for the first time since 2012, Boston reached 100°F, Washington D.C. hit 102°F (39°C), and Philadelphia tied a daily record at 103°F (39°C). Atlantic City, New Jersey, tied its all-time high of 106°F (41°C) on July 4.
As Wikipedia documents, at least 44 heat-related fatalities were reported from the first phase of the heat wave: 29 in New Jersey, 7 in Pennsylvania, 4 in Illinois, 3 in New York, and 1 in Mississippi. The extreme heat also strained infrastructure severely. PJM Interconnection, which serves 67 million people, neared its record for power demand, and the U.S. Department of Energy ordered all electrical generators to run at full capacity.
The Danger of Hot Nights
Health experts warn that high overnight temperatures pose a greater danger than scorching daytime highs. When the body’s core temperature cannot cool down and recover at night, the cumulative effect can be deadly.
“That’s where the health outcomes are amplified, particularly for the elderly and vulnerable communities,” said Marshall Shepherd, a meteorology professor at the University of Georgia, in an interview with the Associated Press.
Kristie Ebi, a public health and climate scientist at the University of Washington, told the AP that “mortality starts the second or third day” because the body is unable to cool. She emphasized that heat-related illness can creep up unnoticed: “It’s hard to know you’re getting in trouble with the heat. This is why we need to be more proactive.”
A Second Heat Dome Forms
Following the eastern heat dome, a second heat dome is now forming over the western and central United States. Phoenix, Arizona, reached 113°F (45°C) from July 6–8, and Salt Lake City, Utah, recorded a new all-time high of 109°F (43°C) on July 12, according to USA Today. Heat advisories are also in effect in the Southwest and Alaska.
The heat dome has also helped fuel wildfires in the western United States, compounding the region’s challenges.
Infrastructure Under Strain
The ongoing heat wave has exposed critical vulnerabilities in U.S. infrastructure. Amtrak reduced speeds in the Northeast Corridor, while SEPTA and NJ Transit faced delays and cancellations due to heat-related rail issues. Over 1.3 million power outages occurred from severe thunderstorms between July 4 and July 6, following an earlier outage that left 250,000 without power in New Jersey alone on July 3.
The power grid remains under immense pressure. The Department of Energy took the unusual step of ordering all generators to run at full capacity — the second time this summer such an order has been issued.
Climate Context
The 2026 heat wave is unfolding against a backdrop of accelerating climate change. The National Weather Service confirmed El Niño conditions on June 11, with the potential for a “Super El Niño” developing later in the year. Climate scientists attribute the increased severity, duration, and frequency of heat waves to human-caused climate change, noting that such events are becoming “virtually impossible” without fossil fuel-driven warming.
A heat dome occurs when a high-pressure system traps hot air beneath it, acting like a lid on a pot. The compressed air heats up further, creating a self-reinforcing cycle of extreme temperatures. Experts say heat waves are “tending to last longer, be stronger, and often more intense.”
What to Watch For
With the second heat dome now settling over the western half of the continent, officials are urging residents to take precautions: stay hydrated, seek air conditioning, check on elderly neighbors and family members, and be aware of early warning signs of heat-related illness, including heavy sweating, muscle cramps, and headache.
As the nation endures what is shaping up to be one of the most extreme heat events in recent memory, the key questions remain: How many more records will fall? Will the power grid hold? And what long-term adaptation measures will emerge from a summer that has already proven deadly?