The D.C. area will get a bit of a break over the next few days from the hot and muggy weather. But this is already one of the most humid summers on record.
According to weather data from Reagan National Airport, the area has experienced over 650 hours with a dew point over 70 degrees since June 1.
The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity of 100%. “The higher the dew point rises, the greater the amount of moisture in the air. This directly affects how ‘comfortable’ it will feel outside,” according to the National Weather Service.
“Once you get dew points above 70 degrees, it starts to be uncomfortable,” WTOP Meteorologist Mike Stinneford said.
“This summer, we’re seeing dew points in the upper 70s to lower 80s. One day last week, right before the big storms came in, Gaithersburg had a soupy 83-degree dew point,” he said.
That’s why when you are sweating outdoors, you get no evaporation cooling effect because the air is full of moisture, “even just walking, you get soaked with perspiration,” Stinneford said.
In the D.C. area, the average number of hours with above 70-degree dew points from June 1 to mid-July is usually about 276 hours, less than half what the area has experienced this summer, making it one of the most humid on record.
There is a combination of things at work leading to the humid conditions. First, a ridge of high pressure has been pumping up tropical moisture from both the Atlantic and the Gulf.
Second, there’s a significant amount of moisture in the ground right now, which is a source for a lot of humidity.
There is some good news, though. All the extra moisture in the air has led to more rainfall, ending the area’s drought last month.
The Metropolitan Washington Council of Governments said regional experts met last month and concluded that drought conditions have improved significantly.
According to 7News First Alert Senior Meteorologist Brian van de Graff, Reagan Airport’s rainfall level is two and half inches above average for the year and just .63 inches below average for the month of July.
Rainfall at Dulles Airport is down to an inch over the average for the month and just shy of two inches for the year.
But overall, the entire region, except around Baltimore, is out of drought territory.
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