"Temperatures will be generally 100 to 105 degrees Thursday and Friday. The mid-Atlantic is running 10 to 15 degrees above normal. This is a life-threatening heat event.
"National Weather Service
175million Americans under major or extreme heat risk
What is a heat dome?
A heat dome forms when a high-pressure system stalls over a region and traps hot air beneath it like a lid on a pot. The trapped air sinks, compresses, and heats further. This one parked over the central United States in late June 2026 and expanded east in time for the Fourth of July holiday, when cooling centers and emergency rooms began filling up from the Midwest to New England.
Heat index peak, mid-Atlantic
up to 115 degrees Fahrenheit
Cities that broke or tied daily records July 3
at least 20
NYC LaGuardia midnight temp
94F, an all-time midnight record
Americans under some level of heat alert
over 200 million
Nights are the hidden danger. Urban areas are struggling to drop below 80F overnight, giving bodies no chance to recover before the next day of extreme heat. The body needs cooler nights to repair heat stress; without them, risk of heat stroke compounds each day.
More than 200,000 customers lost power Thursday evening as air-conditioning demand strained the grid. The Department of Energy issued emergency orders to increase generation on the PJM Interconnection, which covers the mid-Atlantic and parts of the Midwest.
Stay hydrated before you feel thirsty. By the time thirst kicks in, the body is already behind on fluids in this kind of heat.
Check on elderly neighbours and anyone without air conditioning. Heat kills more Americans each year than any other weather hazard, and most deaths are preventable.