At least one person died as severe weather erupted across a vast stretch of the United States on Sunday amid warnings of widespread damaging winds, tornadoes and hail as large as baseballs.
A tree fell on a travel trailer that was camped along the Illinois River between Tahlequah and Kansas, Okla., during heavy winds early on Sunday morning, trapping a couple inside, said Sheriff Jason Chennault of Cherokee County.
The man was pronounced dead at the scene, and the woman suffered minor injuries, Sheriff Chennault said.
The highest risk on Sunday covered a large area from northeastern Texas and northern Louisiana through Mississippi, northwestern Alabama, Illinois, Indiana, Ohio and southern Michigan, potentially affecting a population of more than 40 million people.
The Storm Prediction Center placed these areas under an enhanced risk level of three out of five on the severe weather scale.
Tornado watches popped up across Arkansas, Illinois, Indiana, Kentucky, Missouri and Tennessee on Sunday afternoon, according to the National Weather Service.
A few strong tornadoes could be expected, the National Weather Prediction Center said.
On Sunday night, trees and power lines were down in Ingham County, Mich., which is northwest of Ann Arbor and has a population of about 284,000.
Rob Dale, a deputy at Ingham County Emergency Management, said some houses were damaged but there were no reports of serious injuries. About 10 percent of the county is without power, and a damage assessment was underway, he said.
The volatile setup was being driven by a cold front linked to a storm system that is moving through the Great Lakes and will collide with warm, moisture-rich air in the South, creating prime conditions for powerful thunderstorms.
“To the warm side of that front in the South, we’ll have enough moisture and instability to get thunderstorms, and some of them could be severe,” said Marc Chenard, a meteorologist at the Weather Prediction Center.
The risk is expected to intensify on Sunday evening.
The threat was expected to escalate Sunday evening, as storms that initially develop across Missouri and Illinois intensify while spreading into Arkansas, Louisiana and Texas and the Lower Mississippi and Tennessee Valleys.
The Storm Prediction Center said the severe potential will persist into Sunday night, as the storms merge into larger and more intense outbreaks.
The greatest threat for tornadoes is expected in eastern Arkansas, northern Mississippi, western Tennessee, western Kentucky, southeastern Missouri and southern portions of Illinois and Indiana. Some tornadoes could be strong.
Forecasters also warned of very large hail, up to three inches in diameter, that would most likely fall across northeastern Texas, northwestern Louisiana, Arkansas, southeastern Missouri, Southern Illinois and western Ohio. Parts of western Kentucky and Tennessee may also be at risk.
Threats will move east on Monday.
The severe weather risk will shift east on Monday. The greatest risk will stretch from Virginia southwestward into Alabama, Georgia and the Florida Panhandle, where storms are expected to be more intense.
In the Northeast, including parts of New York, the primary threat will be strong wind gusts. Farther south, the storms are expected to be embedded with tornadoes and bring very large hail.
The Storm Prediction Center has placed southern Alabama, Georgia, South Carolina, North Carolina and much of Virginia under an enhanced risk level, three out of five, for severe weather on Monday and into Tuesday.
The storms are forecast to continue into the night, as they push toward the East Coast before eventually moving offshore.
However, this may not be the last round of severe weather.
“It’s an active period,” Mr. Chenard said. “Another system is likely to be following behind it.”
Alexandra E. Petri contributed reporting.
