The summer of 2025 has brought about record humidity extremes across the area east of the Rockies. Average dew points since 1950 have gone up vertically, turning this summer into a uniquely sultry one. The recent increase in moisture has had an extremely uncomfortable effect on most of the region. It has contributed to unprecedented nighttime heat extremes and a worrying change in summer weather patterns.
Meteorologists have never seen a trend this large. The average summer dew point in this region has increased by over 2.5 degrees since the mid-20th century. In fact, the average June and July dew points have breached 66 degrees. This represents the highest through-fall levels ever recorded since monitoring started in 1950. This significant rise in humidity is not a fleeting phenomenon; it is indicative of a broader trend that is reshaping summer experiences for residents.
In fact, four of the last six summers have featured at least one month with excessively high dew points. In nearly all of these summers, the average temperature was at or above 65 degrees. As the temperature increases in the summer months, particularly in the southern United States, average dew points are much higher. By comparison, northern states see drastically lower numbers. With increased moisture content in the atmosphere, the quality of cooling that happens at night is diminished, creating dangerous temperatures that residents cannot escape.
Nighttime Temperature Records Shattered
Its effects this all-pervasive humidity have been powerfully felt from the Carolinas to Ohio. Cities like Raleigh North Carolina, Charlotte North Carolina, Nashville Tennessee, Virginia Beach Virginia and Wilmington North Carolina recorded all time overnight low temperature highs thanks to the high dew points. That stickiness in the air has resulted in the shattering of high temperature records all across the Ohio Valley, Mid-Atlantic, and coastal states.
This tragic phenomenon is far too common across the country. Areas in 27 states and Washington, D.C., have experienced an alarming increase of days over walking-on-hot-coals levels of 77° daily dew points. Philadelphia baked through 29 days the past three summers where dew points climbed to at least 75 degrees. Washington wasn’t too far behind, with 27 days. Meanwhile, Baltimore sweltered through 24 days of extreme humidity.
“This has been a very muggy summer. The humid heat has been way up,” – Bernadette Woods Placky
This year, cities like Washington, Baltimore, Pittsburgh, Richmond, Columbus, and St. Louis have dew points averaging a full six degrees or more above their historical averages. These standards were set between 1951 and 2020. These conditions signal a troubling trend, one that could have serious consequences on public health and comfort.
The Science Behind Humidity Increases
Meteorological experts explain that a basic law of physics contributes to rising humidity levels: for every degree Fahrenheit increase in temperature, the atmosphere can hold about 4% more water vapor. This human health principle highlights why the rise in summer temperatures is accompanied by a rise in summertime humidity.
As local weather and environmental activist Cameron Lee told me, what’s stunning about these dramatic shifts is sometimes they happen over a mere 20 years. His advice was based on his observations, as it should be. He pointed out that his home weather station in Ohio measured dew points reaching as high as 82 degrees. This record-shattering humidity is representative of trends from a warming world’s influence on the eastern U.S.
“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,” – Cameron Lee
Lee noted how radically different modern summers are compared to the seasons enjoyed by generations past.
“Summers now are not your grandparents’ summers,” – Cameron Lee
Understanding how humidity is trending over time can help us better understand the source of discomfort many of our residents are experiencing this summer.
Impacts on Health and Well-Being
The effects of high humidity go far beyond discomfort, with serious consequences for public health. As Taylor, a trained meteorologist, said, when temperatures remain high, the body can’t cool down sufficiently at night. Unfortunately, high humidity levels only compound the problem.
“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,” – Taylor
This lack of recovery contributes to fatigue and other serious health issues. It’s difficult enough for people who have access to air conditioning or cooling centers. Such conditions can be life-threatening, especially during multi-day extreme heat events.
Given the ongoing impacts of climate change, as summer continues, people living in impacted communities/areas will have to be more vigilant about protecting their health. Understanding available, local resources, such as cooling centers and their hours of operation, is critical. Such resources can dramatically increase well-being on the hottest of humid days.