Death toll rising after tornadoes rock America's Heartland over Memorial Day weekend

( Fox )

At least eight people were killed during a severe weather outbreak over Memorial Day weekend that brought tornadoes and tennis-ball-sized hail and knocked out power to thousands across the Southern Plains overnight on Sunday.

The worst of the storm hit in the overnight hours when at least 20 tornadoes were seen by radar or in person across the region, according to the FOX Forecast Center. Storm damage was reported in Texas, Kansas, Missouri, Oklahoma and Arkansas.

Some of the most devastating damage in Texas happened outside the Dallas-Fort Worth area, where Cooke County Sheriff Ray Sappington said in a news conference that five people were killed and dozens were injured at a travel center off Interstate 35 near Valley View. The sheriff said children were among the dead. 

Denton County officials said a tornado moved into the northern part of the county late Saturday, damaging homes, flipping RVs and ripping down power lines in the area.

Major damage was reported at Lake Ray Roberts Marina and RVs.

The Denton Fire Department said multiple victims were trapped in the property above, and major damage was reported along the Denton-Cooke County line. 

An 18-wheeler overturned on I-35 taking down powerlines and stopping traffic for several hours, county officials said. 

A lone supercell part of the severe storms started in northeastern Oklahoma and continued along the Missouri-Arkansas state lines causing widespread damage along its path. 

In northeastern Oklahoma, two people were killed and others were injured after a tornado hit Mayes County, according to emergency management officials.

Mayes County Emergency Management Director Johnny Janzen said the majority of the damage was near East 427 and West 470 Road. 

At least one possible tornado and wind gusts over 60 mph caused damage in Bentonville, Arkansas.

Benton County Judge Barry Moehring said in a news conference that officials have confirmed multiple injuries on the east side of the county and at least one death. 

City officials said Black Hills Energy has been responding to gas leak calls in Benton County after the storm.

Customers who smell natural gas are being told to leave their homes immediately and call 911.

On Sunday morning, more than 300,000 people in five states were without power, with the majority of outages in Missouri and Arkansas. 

Powerful storms continue through Sunday

Severe thunderstorms are expected to move northeast and impact the Mississippi, Tennessee and Ohio valleys.

Unlike Saturday, when development chances were prime during the evening, Sunday will feature showers and thunderstorms throughout the day that could impact events.

"This storm system is going to bring its slow movement," said FOX Weather Meteorologist Jane Minar. "A cold front is going to trigger up those storms as we get into the afternoon, with dew points well into the 70s and daytime heating, and we have a threat for some pretty serious storms, damaging winds, an isolated tornado and flooding concerns."

The SPC has highlighted over 16 million in communities such as St. Louis, Nashville, Cincinnati, Springfield, Illinois and Louisville, Kentucky in an early Level 3 out of 5 risk for severe weather. That area also includes Indianapolis, where the iconic Indy 500 is scheduled to race that morning and where organizers are already preparing for the potential of rain. Strong tornadoes, wind gusts over 75 mph and golf ball-sized hail are all possible in the Level 3 risk zone.

But another 27 million are currently in a Level 2 risk of severe weather, including Chicago, Memphis and Kansas City. 

Fortunately for travelers, many are already at their destinations by Sunday. However, those who will be traveling on interstates 40, 70, 55 and 65 will want to pay close attention to the forecast.

Severe weather threat shifts to mid-Atlantic on Memorial Day

On the holiday itself, there is expected to be a large spread of showers and thunderstorms across much of the eastern third of the nation. Chances for a severe weather outbreak are much decreased than during the previous two days. 

Still, the SPC has placed just over 27 million people in the mid-Atlantic in a Level 2 severe weather threat, including Washington, D.C.; Baltimore and Charlotte and Raleigh in North Carolina.