AUSTIN, Texas (AP) — A mess of ice, sleet and snow lingered across much of the southern U.S. as thousands in Texas endured freezing temperatures with no power, including many in the state capital of Austin, but a warming trend was forecast to bring relief from the deadly storm Thursday.

More than 390,000 customers in Texas were without power early Thurdsay as trees, heavy with ice, buckled onto power lines, according to PowerOutage, a website tracking utility reports.

More than 150,000 of those outages were in Austin, where the city’s utility warned residents who had been without electricity that lights and heat may not come back on until later Thursday.

Pablo Vegas, who heads the Electric Reliability Council of Texas, vowed the state’s electrical grid and natural gas supply would be reliable and there wouldn’t be a repeat of the February 2021 blackouts when the grid was on the brink of total failure.

School systems in the Dallas and Austin, plus many in Arkansas and Memphis, Tennessee, planned to be closed Thursday as bands of winter precipitation continued to push through.

Nearly 700 flights scheduled for Thursday already had been canceled by Thursday morning, according to the flight tracking service FlightAware.com. That followed thousands of cancelations and delays since frigid weather set in Monday.

Watches and warnings about wintry conditions were issued for an area stretching along the West Texas border with Mexico through Oklahoma, Arkansas and Louisiana and into western Tennessee and northern Mississippi.

The treacherous driving conditions resulted in at least eight deaths on slick roads since Monday, including seven in Texas and one in Arkansas. Republican Texas Gov. Greg Abbott urged people not to drive.