The National Weather Service in Norman, Okla., said large hail will be the primary risk in that state this morning, with the tornado threat ramping up in the afternoon. The high risk zone is meant to warn about weather events that are "long-lived, very widespread, and particularly intense". The severe threat will be concentrated from west Texas and the Texas Panhandle eastward across Oklahoma, Kansas into western Missouri and western Arkansas.
After a brief break, the risk of severe thunderstorms will increase again, the National Weather Service's Fort Worth office said.
The threat of severe storms will spread across a vast area Saturday, including Texas to southern Minnesota, CNN Meteorologist Derek Van Dam said.
More than 5.4 million people across the Southern Plains are under a high threat of violent tornados Monday, with 1.4 million facing at least a 45% chance of a deadly storm.
Parts of Oklahoma and Texas are bracing for what could be a tornado outbreak today.
Violent tornadoes account for only about 0.5 percent of all tornadoes but are responsible for about half of all tornado deaths, CNN meteorologist Brandon Miller said.
Violent tornadoes, very big hail and detrimental winds are all doable from northern Texas to southern Kansas on Monday.
"Impressive thunderstorm cells" forming over the area could be unsafe because many people are still sleeping and "any tornadoes that do potentially form will be hidden by darkness", Van Dam said.
Another round of severe weather is forecast for Texas, Oklahoma and parts of the Southern Plains, including the possibility of tornadoes.
Flickinger expected to storm chase in Texas but headed to North Platte, Nebraska instead. That line of storms is expected to move east of Dallas by mid morning Tuesday.
Storms spread across the Great Lakes/Ohio Valley area and most of the Northeast on Sunday. Intense tornadoes, grapefruit-sized hail and winds over 70 miles per hour are likely with storms that develop in this area.