Tornadoes and Storms Leave 18 Dead and 500,000 Without Power

More than half a million customers across nine states from Texas to Pennsylvania had no power early Monday morning, after powerful storms and tornadoes over the weekend left at least 18 people dead.

There were nearly 200,000 outages in Kentucky as of 4 a.m., and more than 200,000 customers were without power across Arkansas, Kentucky, Missouri, Virginia and West Virginia, according to the tracking site poweroutage.us. Gov. Andy Beshear of Kentucky said early Monday that he had declared a state of emergency.

As thunderstorms continued overnight, more than 12 million people in the Southeast and Midwest were at one point under tornado watches, indicating that tornadoes were possible, according to the National Weather Service. Most of those warnings were set to expire by 6 a.m. Eastern time Monday.

More heavy rain and thunderstorms are expected when the storm system moves from the Ohio Valley into the Mid-Atlantic and the Northeast later on Memorial Day, the Weather Service said in a forecast.

The system is the latest to pummel the region over the past few days. Five people were killed and part of a city was obliterated in Iowa last week after a powerful tornado hit.

On Sunday, severe thunderstorms in Howell County, Mo., produced hail the size of baseballs and tornadoes that downed trees and damaged homes near the town of Mountain View, said Kelsey Angle, a meteorologist with the National Weather Service in Springfield.

Forecasters said the storms forming over Missouri were predicted to grow overnight as they moved east, blowing strong winds into Kentucky and Tennessee.

“Really, Kentucky and Tennessee will be in the cross hairs for the damaging winds,” said Bill Bunting, a meteorologist with the Weather Service’s Storm Prediction Center in Norman, Okla. He said that tornadoes and hail of up to three inches or more in diameter were possible.

Governor Beshear said that power lines were down across Kentucky, and that there had been reports of tornadoes and wind damage. As of Sunday afternoon, there was one confirmed death statewide but no other reported injuries.

“We have gotten through at least the first part of this event,” Mr. Beshear said, speaking from a command center. “And we want to make sure we don’t lose anybody else.”