70 million Americans have sweated through the muggiest summer on record

According to the numbers, more than 70 million Americans sweated through the muggiest first two months of summer on record.

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.

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

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 the weather service office in Tampa calls oppressive.

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.

High humidity doesn’t allow the air to cool at night as much as it usually does, and the stickiness contributed to multiple night temperature records from the Ohio Valley through the Mid-Atlantic. 

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.

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.

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 warmer it gets.