Millions of Americans are planning to attend Fourth of July parades, barbecues, and fireworks displays this weekend, but meteorologists warn that spending time outdoors could be dangerous as an intense heatwave brings record-breaking temperatures to central and eastern states.
The National Weather Service expects a strengthening heat dome to build across the center of the nation and gradually expand eastward this week, producing temperatures in the 90s and low 100s Fahrenheit (30s Celsius). The bigger concern, however, will be wet bulb temperatures. The combination of extreme heat and high humidity will make it feel as hot as 115 degrees F (46 degrees C) across parts of the southern Plains, the mid-Mississippi Valley, and eventually the Mid-Atlantic, according to the NWS.
“No exaggeration to say that the severity of the heatwave that the Eastern U.S. is about to experience will be cruel and grueling for days!” Jeff Berardelli, chief meteorologist and climate specialist for WFLA Tampa Bay, posted on X on Sunday. “[Hundreds] of record highs, some neck and neck with all-time records, in the East Coast cities!”
Heads up‼️ Hottest Ever?! It’s genuinely possible. No exaggeration to say that the severity of the #heatwave that the Eastern US is about to experience will be cruel and grueling for days! 100s of record highs, some neck and neck with all-time records, in the East Coast cities!… pic.twitter.com/pX5XdjlbDV
— Jeff Berardelli (@WeatherProf) June 28, 2026
Why hot, humid weather is so dangerous
Much of the central and eastern U.S. will be under a Moderate to Major HeatRisk (the NWS index for potential heat-related health risks) for Monday and Major to Extreme HeatRisk for Tuesday, the agency stated Monday morning. On the Fourth of July, more than 60 million Americans across the East—including major cities such as New York, Philadelphia, Washington, D.C., Charlotte, Cincinnati, and Nashville—will be under Extreme HeatRisk.
That means conditions will be “very dangerous to anyone without proper hydration or adequate cooling,” according to the NWS. The agency advises against spending extended periods of time outdoors even in the evening, as forecasters don’t expect much nighttime relief.
Extremely hot, humid weather is dangerous because the body lowers its temperature primarily through evaporative cooling. When sweat evaporates, it cools the surface of the skin. Humidity inhibits this process, increasing the risk of heat-related illness.
How to prevent heat-related illness
Infants, young children, the elderly, pregnant people, and people with chronic health conditions are among those most vulnerable to heat-related illness, but under Extreme HeatRisk, the entire population is at risk. Heat stroke is a life-threatening medical emergency that can set in quickly, so it’s crucial to know the signs.
Changes in someone’s mental state or behavior (such as confusion or agitation), flushed skin that feels hot and dry to the touch, nausea, vomiting, rapid breathing, racing heart rate, and headache can all be symptoms of heat stroke, according to the Mayo Clinic.
During a severe, prolonged heatwave, it’s essential to take precautions—even on the Fourth of July. While many enjoy spending time outside over this holiday weekend, the NWS recommends that people under Extreme HeatRisk seriously consider canceling outdoor activities. If you do choose to go out, taking frequent breaks in air conditioning and staying hydrated will be key.
Even moderate levels of physical exertion can increase the risk of heat-related illness. If you plan to run, hike, bike, play sports, or even go for a walk, you will need to take the forecast into consideration. If you can cancel or reschedule these plans for the coolest part of the day, experts advise that you do so.
Extreme heatwaves like this one are occurring more frequently as the global temperature rises, so learning how to stay safe during these events will only become more important. This week’s heat and humidity are sure to put a damper on holiday plans for many, but there are ways to celebrate without putting yourself at greater risk.
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