A powerful winter storm that dumped heavy snow and icy roads across much of Texas and Oklahoma moved east into southern U.S. states overnight, prompting governors to declare a state of emergency and close schools across the region.

Arkansas Governor Sarah Sanders mobilized the National Guard to help stranded motorists. On Friday, school classes were canceled for millions of children in large parts of the southern states from Texas to Georgia and as far east as South Carolina.

The heaviest snowfall was expected Friday across the northern half of Arkansas and much of Tennessee, with totals ranging from 6 to 9 inches (about 15 to 22 centimeters) in some parts of those states, according to the National Weather Service.

Farther south and east in Louisiana, Mississippi and Alabama, a wintry mix of sleet and freezing rain made travel treacherous.

The storm dropped up to 7 inches (about 18 centimeters) in some places in central Oklahoma and northern Texas before moving into Arkansas. More than 4,500 flights were delayed and another 2,000 were canceled on Thursday. Further delays and cancellations are expected for Friday.

“I didn’t see any accidents, but I did see a few people getting stuck on the road and sliding around,” said Charles Daniel, a truck driver who was hauling a 45-foot-long trailer loaded with auto paint parts and parts Other supplies drove along slick, muddy roads in central Oklahoma on Thursday. “People don’t have to drive.”

The polar vortex of ultra-cold air usually revolves around the North Pole, but sometimes it spreads south into the United States, Europe and Asia. Some experts say such events are paradoxically becoming more common as the world warms.

The cold snap coincided with rare wildfires in January that hit the Los Angeles area.

Snow and sleet hammer Texas, Oklahoma

Paul Kirkwood, a meteorologist with the National Weather Service, said the storm that swept through the Dallas area will produce a “swath of snow” that will hit parts of Mississippi, Georgia, Tennessee, Kentucky, North Carolina and South Carolina.

Texas Gov. Greg Abbott urged residents to avoid driving if possible. The roads could be dangerous as 75,000 fans were expected at AT&T Stadium in Arlington on Friday for the college football championship semifinal between Texas and Ohio State in the Cotton Bowl.

Unease in the South

The system was expected to move northeast to coastal Virginia and North Carolina by Friday with heavy snow and freezing rain. Up to 8 inches (about 20 centimeters) of snow could fall in parts of Georgia, North Carolina, Tennessee and West Virginia by Saturday, the weather service said.

Georgia Gov. Brian Kemp declared a state of emergency Thursday as the northern half of the state braced for snow and ice starting Friday morning. Weather service forecasters warned that snow and ice would likely accumulate in the Atlanta area, making roads treacherous and possibly leading to power outages.

Public school systems in metro Atlanta and northern Georgia canceled in-person classes for Friday as more than a million students had a snow day or were ordered to stay home to learn online.

In Tennessee, Memphis-Shelby County Schools, the state’s largest district with more than 100,000 students, closed all schools on Friday. With up to 8 inches of snow forecast for Memphis, officials said two warming centers would be open around the clock to provide shelter for people needing to escape the cold.

The Carolinas are preparing

Parts of South Carolina braced for their first wintry weather in three years. The state Department of Transportation dusted off its brine and salt supplies and began treating highways and other major highways from Columbia north on Thursday. School systems in these areas will either close early on Friday, close all day, or host online learning days.

In North Carolina, Gov. Josh Stein declared a state of emergency ahead of the storm, which forecasters said could bring up to 3 inches (7.6 centimeters) of snow in many parts of the state, and even more in mountainous areas. Sleet and freezing rain were also likely.

The approaching storm led to the cancellation of a public outdoor dedication ceremony for Stein and other statewide elected officials Saturday in Raleigh.

A boil water order for Virginia’s capital city

Water was brought to a boil in Richmond, Virginia, as officials worked to restore the water reservoir system, which was closed Monday after a storm caused a power outage, Mayor Danny Avula said.

The city of more than 200,000 distributed bottled water at 11 locations and delivered it to elderly residents and others who could not reach those locations, officials said.

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Associated Press reporters Sean Murphy in Oklahoma City, Adrian Sainz in Memphis, Tennessee, Heather Hollingsworth in Kansas City, Charlotte Kramon in Atlanta, Jeffrey Collins in Columbia, South Carolina, Nadia Lathan in Austin, Texas, Ben Finley in Norfolk, Virginia, Andrew DeMillo in Little Rock, Arkansas, Kimberly Chandler in Montgomery, Alabama, John Raby in Cross Lanes, West Virginia, and Dylan Lovan in Louisville, Kentucky, contributed to this report.

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