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September-like cool air to plunge into midwestern, northeastern US

By Alex Sosnowski, AccuWeather senior meteorologist
June 26, 2017, 1:51:30 AM EDT

Much cooler air with temperatures more typical of mid- to late September will sweep across the Great Lakes and Northeast early this week.

"Temperatures will stay below average through midweek," according to AccuWeather Long-Range Meteorologist Max Vido.

However, as the core of the cool air settles overhead, temperatures will be held to the 60s and lower 70s in the Great Lakes and the northern and central Appalachians. Parts of the upper Great Lakes will fail to climb out of the 50s.

Early week cool June 25

Along the I-95 corridor, highs will be trimmed to the middle and upper 70s for Tuesday.

Temperatures will dip into the 40s and lower 50s in much of the Midwest and the 50s to around 60 F along the Atlantic Seaboard at night.

Toledo, Ohio, and Pittsburgh are among a few of the communities that will challenge record lows.

chilly nights June 25

Low humidity will accompany the cool air. The less humid air will not only be felt as far to the east as the New England and mid-Atlantic coasts, but also into the Deep South.

The only real difference in how it will feel compared to September will be the strong June sunshine. Where and when the sun is out, it will still feel warm, especially in your car.

Never leave children and pets unattended in a vehicle. Heat can build up to dangerous levels in a few minutes regardless of the outside temperature this time of the year.

"Do not assume that the cooler air will lessen the risk of getting a sunburn," AccuWeather Senior Meteorologist Kristina Pydynowski said. "Even when the temperature is stuck in the 60s, the sun’s rays are just as strong as when highs reach the 80s and 90s."

The extensive swath of cool air with low humidity will translate to lower electricity usage when compared to average for late June.

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Many people will be able to turn off their household air conditioner and basement dehumidifier.

Most days along the Atlantic coast will still be warm enough for swimming and other summer outdoor activities. However, temperatures may dip low enough to hinder a jump in the pool from the Great Lakes to the Appalachians.

Showers and thunderstorms will also interfere with some outdoor plans from the Great Lakes to the Northeast, since the air aloft will be unusually chilly for June. Some thunderstorms will produce small hail.

NE June 25

"The air may get cool enough to allow a couple of waterspouts to form over the Great Lakes through Monday," AccuWeather Senior Meteorologist Dave Dombek said.

Small craft operators should be alert for rapidly changing weather conditions. Boaters, as well as swimmers, will also face rough seas.

"Much like what we see in the winter with persistent lake-effect snow bands, there is the concern for showers and thunderstorms to repeat over the same areas downwind of Lake Erie into western New York Monday and Monday night," AccuWeather Meteorologist Jake Sojda said. "Localized flash flooding may result."

"The risk for flash flooding will be low elsewhere in the Great Lakes and Northeast," Pydynowski said. "With less moisture in the atmosphere, downpours will be less intense as what occurred last week."

More violent thunderstorms will threaten the western Great Lakes at midweek as the summer heat and humidity begins to make a comeback.

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