40 Million Americans Under Threat for Severe Thunderstorms Thursday

An estimated 40 million people could face large hail and flash floods as storms loom Thursday.

A strong cold front pressing south and east through the nation's Heartland will collide with an exceptionally hot and muggy air-mass to produce widespread thunderstorms into Thursday night, according to the National Weather Service.

The region most at risk for severe storms and excessive rainfall is the central High Plains.

The Weather Prediction Center said there is a moderate risk of excessive rainfall and an enhanced risk of severe weather. The thunderstorms could produce any combination of damaging winds, large hail, tornadoes and flash flooding.

The severe weather and flash flood threat is also present for an area that stretches from southern Kansas and northern Oklahoma all the way to the Tennessee Valley and the southern Appalachians.

There is also a slight risk of severe storms over portions of the northern Mid-Atlantic and in northeast Ohio, as well as areas east of the Mississippi River, including the eastern Great Lakes, the Ohio Valley and parts of the Southeast.

By Friday, the cold front continues farther south and east, placing the best threat for strong-to-severe storms over the mid-South and Northeast.

While the cold front is bringing severe weather and heavy rainfall, it also brings cooler temperatures and more comfortable humidity levels to the northern Plains and Midwest.

By Friday, parts of the Central Plains could see daytime highs that are as low as 15-20 degrees below normal. The reprieve from the heat across parts of the South will arrive by Saturday, and include the mid-Atlantic and Northeast where daytime highs are expected to be several degrees below normal and humidity levels that are more refreshing for mid-late July.

In contrast, the heat wave will be anchored along and west of the Rockies late Friday and into Saturday where more record-breaking heat is forecast.