National Weather Service Warns Dangerous Heat Wave With High Humidity Across U.S. Ahead Of July Fourth

A long and dangerous heat wave is expected to blast a large swath of the United States this week ahead of the July Fourth holiday, with the National Weather Service warning that temperatures will rise and feel even hotter because of high humidity.

CBS News meteorologist Nikki Nolan said more than 100 record-high temperatures are expected through Saturday night, including in New York City and Washington, D.C., which are expected to see record highs into the 100s.

Associated Press

The National Weather Service said high humidity will lead to heat indices of 100 to 110 degrees F (40 C to 43 C), and as high as 115 F (46 C), while nightly lows in the 70s F (21 to 26 C) won't provide much relief.

In the same forecast, the heat wave was described as expanding across the central and eastern U.S., while the Four Corners remain under dangerous fire weather conditions.

The CBS News report also said parts of the U.S., especially Phoenix, Las Vegas, central Texas, and much of the Southwest, were already experiencing temperatures around 100 F.

In Pennsylvania, the Daily American said a dangerous heat wave is expected to impact the state through July 4, 2026, with high humidity making air temperatures feel close to 100 degrees and increasing the risk of heat-related illnesses.

The Daily American quoted Joel Landis, director of the Somerset County Emergency Management Agency, saying, "Preparedness is a shared responsibility."

CBS News

The Daily American also reported that "All seven of our senior centers are available for use as cooling centers to the public," with the public invited to stop in during open hours from 9 a.m. to 2 p.m.

In the broader U.S. forecast, USA TODAY said at least 230 million people in the U.S. — about two-thirds of the U.S. population — could be exposed to extreme heat that could lead to health issues.

USA TODAY added that a heat dome will develop, strengthen and grow in size over much of the central United States for an extended period through the Independence Day weekend.

The National Weather Service warned that the combination of prolonged daytime heating and limited nighttime relief will increase the risk of heat-related illnesses, especially for vulnerable populations and those without adequate cooling, according to the Weather Prediction Center in a USA TODAY report.

“Millions of Americans across the eastern half of the US are facing a prolonged stretch of dangerous heat that’s likely to break records as Americans get set to head outdoors to celebrate the country’s 250th Independence Day”

CNN

NPR said a heat dome is driving the heatwave and quoted NWS forecaster Bryan Putnam explaining, "you combine that with the humidity, those heat indices will go well into the 100s".

NPR also quoted Missouri State Emergency Management Agency guidance that everyone should "plan accordingly and limit prolonged outdoor exposure if possible."

CNN reported that the heat wave is expected to peak by Friday, just in time for the long Fourth of July weekend, with many areas enduring consecutive days of temperatures in the mid-90s to low 100s.

CNN further warned that the heat won't end at sunset, noting that over 250 record warm overnight lows could be challenged this week alone, while the National Weather Service message was that "This heat wave is different."