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90-degree heat to bake Midwest, Northeast prior to cooler, wetter pattern for July's 2nd half

By Alex Sosnowski, AccuWeather senior meteorologist
July 14, 2018, 11:27:44 PM EDT

Hot weather will build across the Northeast and parts of the Midwest into early week, before higher humidity levels lead to cooler conditions and perhaps a risk of isolated flooding for July's second half.

The period from July 3 to Aug. 11 is often referred to as the "dog days of summer" and typically brings some of the hottest weather of the year. The term has ancient origins related to the dog star, Sirius, and its position in the sky.

Dog Days

A marginal heat wave in store

Temperatures will trend upward through this weekend. Heat will hover into early week.

"Although common for the middle of July, highs will generally range from the upper 80s to the middle 90s F," according to AccuWeather Lead Long-Range Meteorologist Paul Pastelok.

NE heat builds 7/14

"At this level, temperatures will actually be a few degrees above average," Pastelok said.

In the Northern states, a heat wave is referred to as three or more days with high temperatures of 90 or above.

While this heat wave will not be as potent as that of early July, intense sunshine will still make it feel hotter than the actual temperature by about 10 degrees during the late morning and afternoon hours.

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The weather will be great for swimming, picnics, festivals and ballgames. But be sure to use sunscreen, stay hydrated and take breaks from the sun and the heat.

A few thunderstorms are forecast to push from the Great Lakes region, across upstate New York and into northwestern New England on Saturday.

Storms may sag farther to the south across the central Appalachians on Sunday. However, much of the time both days are likely to be free of rain.

Cooler, wetter days are ahead

"After the episode of heat, a change in the pattern is expected as weather systems are likely to get jammed up from the Atlantic westward to North America," Pastelok said.

"We expect a dip in the jet stream to develop and be centered over the Midwest."

In this position, frequent waves of cool air are likely to invade a large part of the North Central states.

While the bulk of the cool air would stop short of reaching the Atlantic seaboard in this case, daytime highs are likely to be several degrees lower, when compared to this weekend due to high humidity levels.

The higher humidity would ultimately lead to more clouds and rounds of showers and thunderstorms that take the edge off daytime highs.

"Beyond early week, much of the second half of July may bring near- to below-average temperatures in the East and below-average temperatures over a large part of the Midwest and northern Plains," Pastelok said.

Static US Late July

Even in such a pattern, most days will bring highs well into the 80s in the Interstate-95 corridor and highs in the upper 70s to lower 80s in the Appalachians and much of the Midwest.

"And within that pattern, there will still be some very warm days," Pastelok said.

At this level, temperatures will still be high enough for swimming, short sleeves and most outdoor activities.

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However, patterns such as this can lead to localized heavy rainfall.

"We will have to be on guard for isolated flooding in a pattern such as anticipated next week and beyond," according to AccuWeather Chief Meteorologist Elliot Abrams.

The anticipated atmospheric road block over the Atlantic may set up a corridor of frequent showers and thunderstorms somewhere in parts of the East Coast, Appalachians or Midwest.

"There is no way to say for sure or exactly where that will be this far out," Abrams said. "But, the potential is there."

People with outdoor plans and construction activities may have to pick and choose the drier days or parts of the day for outdoor plans as the pattern evolves.

Typically, most showers and thunderstorm activity in the summer occurs from the mid-afternoon to the mid-evening hours. However, as is often the case with the weather, there are likely to be exceptions.

Is summer over after early this week?

While the cooler weather pattern may have some staying power into early August, it cannot be stated that the heat wave into early next will be the last of this summer.

"We still expect plenty of typical hot weather to go around during August," Pastelok said.

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