As a couple of waves of cooler, less humid air cut into typical August heat and humidity, heavy, gusty and locally severe thunderstorms will erupt from the Midwest to the Northeast into Wednesday night.

The first push of cool air will cause a swath of thunderstorms to erupt from northern New England to the central and southern Appalachians.

Radar estimates are showing more than 3.5 inches of rain in Philadelphia, Pennsylvania Wednesday evening where flooding is ongoing and roads, including part of I-76, are closed.

(Image via PennDOT Cam)

Major highways that will be in the path of the storms with blinding downpours, vivid lightning, gusty winds and even hail include Interstates 64, 66, 70, 76, 78, 80, 84, 86, 87, 88, 91 and 93.

The storms are also forecast to develop and move across the Interstate 95 corridor as well.

As a result, the late-day commute in Washington, D.C., Baltimore, Philadelphia, New York City and Boston is likely to be a mess.

As of Wednesday evening, roughly 22,000 people were without power.

"A couple of isolated tornadoes cannot be ruled-out in the severe weather threat for the Northeast," according to AccuWeather Senior Meteorologist Dave Dombek.

The Wednesday evening commute is likely to be a challenge in Midwest cities such as Green Bay and Madison, Wisconsin, where storms are also expected to erupt.

Substantial travel disruptions are anticipated as well as incidents of property damage.

The most common threat from the storms in both areas will be sudden, torrential downpours that can lead to rapid urban and small stream flooding.

Motorists are warned never to drive through flooded areas. The water may be deeper than it appears and could cause your vehicle to stall and render the electrical system inoperative.

In some cases, the road may have been washed away and the vehicle may drift into deep water, sink or flip over and trap occupants inside.

Airline passengers and crews should expect ground stops, flight delays and even cancellations as thunderstorms approach. Thunderstorms pose a significant risk to aircraft during landing and take off due to the risk of shifting, unsteady winds related to microbursts.

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Isolated wind gusts with some of the storms in the Midwest and Northeast are forecast to be in the neighborhood of 70 mph. Winds this strong, which are just shy of hurricane force, can break large tree limbs, knock over poorly rooted trees, trigger power outages and cause minor property damage.

In a few cases, damaging hail may fall from the strongest storms. Hail may be large enough to damage crops, dent vehicles and siding of homes, break windows and strip leaves and small branches from trees.

Be sure to move indoors at the first rumble of thunder. If you can hear thunder, you are at risk to be struck by lightning.

The same cool front from Wednesday over the Midwest will shift eastward and produce heavy, gusty and locally severe storms from the St. Lawrence Valley to part of the Ohio Valley on Thursday.

"The greatest risk of isolated tornadoes with the Thursday afternoon and evening storms will be across southeastern Quebec," according to AccuWeather Senior Meteorologist Brett Anderson.

"The greatest threat for flash flooding with the storms on Thursday will be across parts of the Ohio Valley," according to AccuWeather Senior Meteorologist Randy Atkins.

Reinforcing waves of cooler and less humid air will progress from the Upper Midwest to the northeastern United States in the wake of the storms later this week and this weekend.

However, storms are likely to linger over parts of the central Plains, Ohio Valley and Southeast states, with localized severe weather and an ongoing risk of isolated flash flooding.

Download the free AccuWeather app to stay alert of severe weather advisories. Keep checking back for updates on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.

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