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Uptick in humidity, storms to erase September-like chill in northeastern US late week


After temperatures more typical of early fall chill the Northeast into midweek, an increase in humidity and warmth will set the stage for another round of thunderstorms and flooding downpours by week’s end.

High temperatures will be stuck in the 60s and 70s through midweek across the northern mid-Atlantic and New England, which is 5 to 15 degrees Fahrenheit below normal for late July.

"Some locations, such as Boston, that had high temperatures in the 90s late last week will not get out of the 60s on Tuesday," AccuWeather Senior Meteorologist Mike Doll said.

The change in temperatures will be less dramatic in areas farther south in the mid-Atlantic.

Highs will be held in the lower to middle 80s in Washington, D.C., near 80 F in Philadelphia, and in the 70s F in New York City through midweek.

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For those weary of the recent spell of heat and high humidity in recent weeks, the cooldown will come as welcome relief and paint an ideal picture for outdoor activities such as fishing, hiking, biking and gardening.

The September-like air will also cut down on the high cooling demands that residents of the eastern United States have been facing for the past several weeks.

Residents eager to open up the windows and have fresh air circulate through their homes may get that chance on not one but two nights through midweek.

However, the early taste of fall will be quickly, albeit briefly, swept away as heat and humidity return by late week.

“Warmer and more humid air will nose in from the Great Lakes on Thursday,” AccuWeather Meteorologist Kyle Brown said. “While humidity levels will not be as oppressive as they were last week, this uptick in humidity will still be noticeable.”

For most areas from the northern mid-Atlantic into New England, the most noticeable difference by late week will be the increase in humidity, as the best push of warm air may get cut off farther south.

From the central to the southern mid-Atlantic, temperatures are forecast to return to near-normal levels for late July. Highs will again challenge the 90-degree mark in Baltimore and Washington, D.C., with lower 80s on tap for New York City.

Due to the high humidity, AccuWeather ReelFeel® temperatures may surge back into the middle to upper 90s across the southern mid-Atlantic and middle to upper 80s farther to the north.

While the heat should not reach dangerous levels in most locations, it may force most residents to close the windows and crank up the air conditioning unit yet again.

The resurgence of summer warmth will also fuel an enhanced risk of showers, thunderstorms and another round of potentially flooding downpours.

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“A storm system approaching from the west will spread the threat of wet weather eastward into the mid-Atlantic by Thursday and Friday,” Brown said.

The potential exists for 1-3 inches of rain to fall over similar areas spanning Thursday evening into Friday night, which would only exacerbate ongoing flooding issues and delay recovery efforts.

Creeks and streams may not have an adequate chance to fall back to normal levels before this additional rainfall causes them to accelerate back out of their banks.

Once this storm system pushes eastward off the mid-Atlantic coastline by Saturday, another surge of fall-like air and lower humidity should grace the eastern U.S. with sunshine and gorgeous conditions.

“A sprawling area of high pressure pushing southward from Canada can suppress intense summer heat and humidity from New England to the mid-Atlantic into early next week,” Brown added.

In fact, any prolonged periods of heat and humidity may fail to return to the northeastern U.S. through at least the first week or two of August.