More than 2,800 flights across the United States were delayed or canceled Monday after powerful storms ripped through the parts of the country, mainly in the Southeast and the Ohio Valley.

Data from FlightAware showed that on Monday morning, 2,067 flights within, into or out of the US were delayed and another 758 were canceled.

United Airlines was faring the worst of the American domestic airlines. About 6% of its schedule, or 185 flights, was canceled and another 7%, or 208 flights, was delayed as of 10 am ET. Delta wasn't far behind, with 4% (163 flights) of its schedule canceled and 8% (293 flights) delayed.

The delays and cancellations come after thunderstorms battered parts of Arkansas, Tennessee, Mississippi and the Ohio Valley Sunday evening, according to the National Weather Service's Storm Prediction Center. More than 700,000 people across the region are without power

Meanwhile, more than 50 million people from Arizona to Louisiana faced "oppressive" heat on Sunday in a significant heat wave that is forecast to spread and continue through the beginning of the July 4 holiday week. Experts say it could potentially break several high temperature records across the region.

The three US airports most affected Monday morning are all major hubs for either United or Delta: New Jersey's Newark Liberty, New York's LaGuardia and Atlanta's Hartsfield-Jackson.

Monday's forecast also looks tough for travelers with 100 million people under threat of severe storms, mainly in the Mid-Atlantic.