Severe weather could cool extreme heat in parts of U.S. this week, forecasters say

The calendar may say that it's meteorological fall, but Mother Nature has said otherwise in recent days, with a surge of extreme heat across much of the northern United States.

Now, AccuWeather meteorologists say that rounds of thunderstorms, some severe, will ease the heat, bringing fall-like conditions.

Much of the central Plains has been sweltering under prolonged heat for weeks, and the first days of September have been no exception.

On Sunday, temperatures in Minneapolis surged to 98 degrees Fahrenheit, setting a new daily high-temperature record. The historical average high temperature in early September is around 77 F.

Meanwhile, highs on the first four days of September climbed above 90 F degrees in Omaha, averaging 7.5 F above the historical average.

AccuWeather forecasters say a potent storm, which will spark rounds of thunderstorms, may finally bring an end to the wave of exceptional heat across the northern tier.

Thunderstorms into Tuesday evening are expected from parts of the Upper Midwest and the western Great Lakes all the way to northern Texas.

"The greatest concentration of severe thunderstorms is expected across Minnesota and Wisconsin through the evening," said AccuWeather Senior Meteorologist Matt Benz. The same zone will also face the highest risk for an isolated tornado or two.

Severe thunderstorms may be more widely separated farther to the south, particularly from Missouri to the Red River, which flows along the border of Oklahoma and Texas. However, any thunderstorms could be capable of triggering heavy, flooding downpours, hail, and damaging wind gusts of 60-70 mph.

Farther to the east, temperatures in Chicago have been more than 7 degrees above the historical average for the start of September. The city is well on its way to another heat wave, which is defined as three consecutive days with highs above 90 degrees, and it is expected to see temperatures crashing down following Wednesday's thunderstorms.

The core of the strongest storms Wednesday is likely to be just to the east of Chicago.

Thunderstorms from central Michigan to western Tennessee, northern Mississippi and southern Arkansas will be more likely to turn severe, with the possibility of hail and damaging winds, according to AccuWeather Senior Meteorologist Brett Anderson.

"These severe weather impacts may be more localized in nature, compared to heavy downpours," Benz said.

Behind the severe weather, a drastic change in air mass will bring much-needed relief from the heat.

High temperatures in the 60s are predicted for cities such as Minneapolis and Madison, Wis., by Wednesday, and in the lower 70s for Chicago and Indianapolis, by Thursday. The drop in temperature will be as much as 20-30 degrees below the peak heat from earlier in the week.

While temperatures are expected to trend upward late this week or over the weekend, they are not forecast to return to the extreme levels of earlier in the month. Instead, temperatures will be near, or even a few degrees below, historical averages for the second week of September.

The thunderstorms crossing the eastern U.S. through Wednesday will temporarily erase the heat across the northern Plains and much of the Great Lakes, but it won't remove it from the entire country. Instead, it will squeeze the heat eastward, making for another few hot days in the Northeast.

Residents of New York City have experienced a milder-than-average start to the month of September, but one particular milestone remains elusive: a high of 90 degrees Fahrenheit. In fact, the city managed to stay below 90 degrees for the entire month of August.

There were two instances this summer where the city had two-day stretches of 90-or-greater temperatures, both in July, but no official three-day heat waves have gone down in the books. It's possible that New York City will finally experience its first heat wave of the summer this week, ahead of the late-week wet weather.

A wet and humid end to the week is expected in the Northeast, thanks to the storm and a surge of heat and moisture up the Eastern Seaboard helping to fuel thunderstorms.

These potent thunderstorms crossing the area will make locally damaging winds Thursday and Thursday night possible from southern Canada to northern Virginia, including major cities such as Ottawa, Buffalo, New York, and Washington, D.C.

"The progression of the storms will slow late-week, allowing for thunderstorms to linger in the same areas for longer," explained Benz. As such, drenching downpours could target the same locations Thursday through Friday, heightening the risk of flash flooding.

Locations right along the Eastern Seaboard, such as New York City, Philadelphia, and Washington, D.C., can expect the wet weather to wait until late Thursday night or Friday. In the meantime, temperatures are forecast to rise into the 90s. With high humidity factored in, AccuWeather RealFeel® Temperatures could climb to around 100 F.

AccuWeather forecasters say that while long-lived severe weather risks are not expected to linger past Friday, the wet weather may stick around. Round after round of wet weather is likely to target the Northeast, bringing more opportunities for rain and thunderstorms all the way through the weekend.