Record-Breaking Humidity in the United States

More than 70 million Americans sweated through the muggiest first two months of summer on record as climate change has noticeably dialed up the Eastern United States’ humidity in recent decades, an Associated Press data analysis shows.

And that meant uncomfortably warm and potentially dangerous nights in many cities the last several weeks, the National Weather Service said.

Parts of 27 states and Washington, D.C., had a record amount of days that meteorologists call uncomfortable — with average daily dew points of 65 degrees Fahrenheit or higher — in June and July, according to data derived from the Copernicus Climate Service.

Paul Williams cools off in water while taking a break from yard work in Richardson, Texas, July 31, 2025. (AP Photo/LM Otero, File)

And that’s just the daily average. In much of the East, the mugginess kept rising to near tropical levels for a few humid hours. Philadelphia had 29 days, Washington had 27 days and Baltimore had 24 days where the highest dew point simmered to at least 75 degrees, which even the weather service office in Tampa calls oppressive, according to weather service data.

Understanding Dew Point

Dew point is a measure of moisture in the air expressed in degrees that many meteorologists call the most accurate way to describe humidity. The summer of 2025 so far has had dew points that average at least 6 degrees higher than the 1951-2020 normals in Washington, Baltimore, Pittsburgh, Richmond, Columbus and St. Louis, the AP calculations show. The average June and July humidity for the entire country east of the Rockies rose to more than 66 degrees, higher than any year since measurements started in 1950.

Expert Insights

“This has been a very muggy summer. The humid heat has been way up,” said Bernadette Woods Placky, chief meteorologist at Climate Central.

Twice this summer climate scientist and humidity expert Cameron Lee of Kent State University measured dew points of about 82 degrees at his home weather station in Ohio. That’s off the various charts that the weather service uses to describe what dew points feel like.

“There are parts of the United States that are experiencing not only greater average humidity, especially in the spring and summer, but also more extreme humid days,” Lee said. He said super sticky days are now stretching out over more days and more land.

Impact on Human Health

High humidity doesn’t allow the air to cool at night as much as it usually does, and the stickiness contributed to multiple nighttime temperature records from the Ohio Valley through the Mid-Atlantic and up and down coastal states, said Zack Taylor, forecast operations chief at the National Weather Service’s Weather Prediction Center. Raleigh, Charlotte, Nashville, Virginia Beach, Va., and Wilmington, N.C., all reached records for the hottest overnight lows. New York City, Columbus, Atlanta, Richmond, Knoxville, Tennessee and Concord, New Hampshire came close, he said.

“What really impacts the body is that nighttime temperature,” Taylor said. “So if there’s no cooling at night or if there’s a lack of cooling it doesn’t allow your body to cool off and recover from what was probably a really hot afternoon. And so when you start seeing that over several days, that can really wear out the body, especially of course if you don’t have access to cooling centers or air conditioning.”

Climate Change and Humidity

An extra hot and rainy summer weather pattern is combining with climate change from the burning of coal, oil and natural gas, Woods Placky said.

The area east of the Rockies has on average gained about 2.5 degrees in summer dew point since 1950, the AP analysis of Copernicus data shows. In the 1950s, 1960s, 1970s, 1980s and part of the 1990s, the eastern half of the country had an average dew point in the low 60s, what the weather service calls noticeable but OK. In four of the last six years that number has been near and even over the uncomfortable line of 65.

“It’s huge,” Lee said of the 75-year trend. “This is showing a massive increase over a relatively short period of time.”

That seemingly small increase in average dew points really means the worst ultra-sticky days that used to happen once a year, now happen several times a summer, which is what affects people, Lee said.

Regional Variations in Humidity

Higher humidity and heat feed on each other. A basic law of physics is that the atmosphere holds an extra 4% more water for every degree Fahrenheit (7% for every degree Celsius) warmer it gets, meteorologists said.

For most of the summer, the Midwest and East were stuck under either incredibly hot high pressure systems, which boosted temperatures, or getting heavy and persistent rain in amounts much higher than average, Taylor said. What was mostly missing was the occasional cool front that pushes out the most oppressive heat and humidity. That finally came in August and brought relief, he said.

Humidity varies by region. The West is much drier. The South gets more 65-degree dew points in the summer than the North. But that’s changing.

University of Georgia meteorology professor Marshall Shepherd said uncomfortable humidity is moving further north, into places where people are less used to it.

Summers now, he said, “are not your grandparents’ summers.”

Conclusion

The record-breaking humidity in the United States is a clear indication of the impact of climate change on our environment. As the planet continues to warm, we can expect more extreme weather events, including heatwaves and high humidity. It’s essential to take necessary precautions to protect ourselves from the heat and to reduce our carbon footprint to mitigate the effects of climate change.

Frequently Asked Questions

Q: What is dew point, and how does it affect humidity?

A: Dew point is a measure of moisture in the air expressed in degrees. It’s an accurate way to describe humidity, and high dew points can make the air feel sticky and uncomfortable.

Q: How has climate change affected humidity in the United States?

A: Climate change has increased the average dew point in the United States, especially in the East, making summers feel hotter and more humid. The area east of the Rockies has gained about 2.5 degrees in summer dew point since 1950.

Q: What are the health impacts of high humidity and heat?

A: High humidity and heat can be dangerous, especially for people without access to cooling centers or air conditioning. It can cause heat exhaustion, heat stroke, and other heat-related illnesses.

Q: How can we protect ourselves from the heat and humidity?

A: To protect ourselves from the heat and humidity, we should stay hydrated, stay indoors during the hottest part of the day, and use cooling devices like fans and air conditioners. We should also check on vulnerable neighbors and friends, especially the elderly and young children.

Q: What can we do to reduce our carbon footprint and mitigate the effects of climate change?

A: We can reduce our carbon footprint by using public transportation, carpooling, or driving electric or hybrid vehicles. We can also use energy-efficient appliances, turn off lights and electronics when not in use, and recycle. Additionally, we can support policies and initiatives that promote renewable energy and reduce greenhouse gas emissions.