More than 70 million Americans have endured the muggiest start to summer on record east of the Rockies, according to an Associated Press analysis of climate data. Rising humidity levels, driven by climate change, have made nights uncomfortably warm and potentially hazardous across many Eastern cities.
Data from the Copernicus Climate Service shows that 27 states and Washington, D.C., experienced record numbers of days in June and July with average daily dew points of 65°F or higher—a level meteorologists classify as uncomfortable. During some hours, dew points soared even higher, reaching near-tropical levels. Cities like Philadelphia, Washington, and Baltimore saw multiple days with peak dew points at or above 75°F, conditions deemed oppressive by the National Weather Service.
Dew point, a key measure of atmospheric moisture, averaged at least 6°F above the 1951–2020 norms this summer in cities including Washington, Baltimore, Pittsburgh, Richmond, Columbus, and St. Louis. Overall, the average June–July humidity east of the Rockies hit more than 66°F, the highest since records began in 1950.
“This has been a very muggy summer with humidity much higher than usual,” said Bernadette Woods Placky, chief meteorologist at Climate Central. Kent State University climate scientist Cameron Lee noted extreme dew points near 82°F this summer in Ohio, a reading off the charts for typical measures. He added that both average and extreme humidity days are increasing in frequency and extent.
High humidity limits nighttime cooling, contributing to multiple overnight temperature records from the Ohio Valley to the Mid-Atlantic and coastal states, said Zack Taylor of the National Weather Service. Cities including Raleigh, Charlotte, Nashville, Virginia Beach, and Wilmington set records for hottest overnight lows, while others like New York City and Atlanta came close.
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“When nights don’t cool down, the body can’t recover from daytime heat, which can be dangerous—especially for those without air conditioning,” Taylor explained.
This unusually hot and wet summer pattern compounds climate change effects caused by burning fossil fuels, Woods Placky noted. Since 1950, summer dew points east of the Rockies have risen about 2.5°F on average. Whereas mid-century summers averaged dew points in the low 60s°F—considered noticeable but manageable—recent years often exceed the uncomfortable 65°F threshold.
Lee said this long-term rise means that ultra-sticky days, once rare, now occur multiple times each summer, greatly impacting public comfort and health. As warmer air holds more moisture—about 4% more per degree Fahrenheit rise—the East has been trapped under persistent heat or heavy rains, with few cool fronts to break the pattern until relief arrived in August.
Humidity remains lower in the West, but experts like University of Georgia meteorology professor Marshall Shepherd warn that oppressive humidity is expanding northward, affecting regions unaccustomed to such conditions.
“Summers now are not your grandparents’ summers,” Shepherd said.
Source: Agency