SAN FRANCISCO, Calif. – A winter storm that dropped record-breaking downpours on Los Angeles is expected to pack a powerful mix of snow, sleet and freezing rain – maybe even a tornado or two – as it crawls across the southern United States, triggering flash floods and power outages, snarling air travel and downing trees.

Significant delays at airport hubs such as Dallas, Houston, New Orleans and Atlanta could make a mess for air travelers and ripple across the country through the weekend, forecasters warned.

The cross-country storm which will bring ice and snow from the Southern Plans to the Appalachians is expected to continue into early next week.

More than a dozen states from Nevada to Virginia are under snow, ice and flood alerts. Most of the snow is expected in the Carolinas and southern Virginia.

In North Carolina, Gov. Roy Cooper was expected to declare a statewide emergency ahead of the onslaught. He told residents to hunker down for the first winter storm of the season. According to Duke Energy, as many as 500,000 homes and businesses could lose power.

"This storm comes at a time of year when North Carolinians are usually hearing carols about snow, not actually seeing it. But this time, the real thing is headed our way," Cooper said. "A winter storm’s not a Christmas carol snow. It’s serious, and you need to take steps now to get your family ready."

The National Weather Service issued a winter storm watch for much of western and central North Carolina.

Asheville, North Carolina, is bracing for double-digit depths. Much of the region should see close to a foot to two feet of snow, followed by icy conditions early next week, the Asheville Citizen Times reported.

"All precipitation ends Monday night as a very light snow, but during the day on Monday, expect a cold rain," meteorologist Doug Outlaw told the newspaper. "It's going to be a slushy mess – it'll be a winter wonderland on Sunday, messy on Monday."

Virginia Gov. Ralph Northam put state agencies on alert and warned residents of power outages and dangerous road conditions with the strong storm front on track to pass through western, central and northern Virginia over the weekend.

Oklahoma Gov. Mary Fallin declared a state of emergency for all 77 counties ahead of the winter storm, but the storm that was expected to dump more than half a foot of snow on parts of western and central Oklahoma was downgraded Friday. In Oklahoma City, where freezing rain and snow was expected overnight into Saturday, the winter storm watch was changed to a travel advisory.

High school championship and playoff football games were postponed in Arkansas and Christmas parades in Tulsa, Oklahoma and South Carolina. Parts of north central Arkansas could see "significant winter weather," the National Weather Service said.

So far most major airline hubs were expected to see only rain with the exception of Charlotte, North Carolina, a hub for American Airlines, where icy weather and up to a half-foot of snow were possible Sunday. Airlines are waiving change fees across a number of states.

Heavy rainfall and flooding will be a major threat with this storm, according to AccuWeather Meteorologist Ryan Adamson, spoiling weekend plans to haul home a Christmas tree or hang outdoors holiday decorations in Louisiana, Mississippi, Alabama and Georgia on Saturday.

Southern Texas, including Corpus Christi and Houston, has the greatest risk of severe weather, including isolated tornadoes, he said. Much of southeast Texas is under a flash flood watch as the storm threatens to drench some parts of the region with up to 10 inches of rainfall.

Houston residents were urged to stay home Friday night and to clean up fallen leaves and debris that could clog storm drains. The worst of the storm is expected to be overnight into Saturday morning.

"As severe weather approaches, it is imperative that Texans heed all warnings from first responders and local officials," Texas Gov. Greg Abbott said Friday. "I encourage all Texans to stay alert to potentially hazardous road conditions and changing weather patterns. Texas is prepared to respond and offer the necessary assistance to local communities as they deal with the impact of this storm."

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By Saturday, the rain and flood threat will shift to the Deep South and Southeast. Along the northern edge of the storm, from Missouri to the Carolinas, more freezing rain and ice is likely.

Late Saturday and through Sunday, the storm is forecast to blanket the central and southern Appalachians with heavy snow, potentially crippling the region. Snow and ice is expected to extend from eastern Oklahoma to the southern Appalachians late Sunday.

In Southern California, evacuation orders were lifted or downgraded Thursday night and Friday morning as the storm moved out of the area.

Downtown Los Angeles got a record 1.9 inches of rain, nearly double what it got in 1997, the previous record, according to the National Weather Service. The storm brought flooding, mudslides and nightmarish traffic and caused roofs to collapse and a plane to skid off a wet runway at Hollywood Burbank Airport. One man being pulled by an SUV was spotted surfing on a flooded street.

Heavy snow closed Interstate 5 between Los Angeles and the San Joaquin Valley for hours causing backups for miles. The San Gabriel Mountains got four to five inches of snow and a foot of snow above 6,000 feet, the National Weather Service said.

There were no reported injuries associated with the mudslide or debris flows and no homes were seriously damaged, according to the Associated Press. Multiple people had to be rescued in Los Angeles, Orange, Riverside and San Diego counties as water flooded roadways, submerging cars. More than 300 people in a San Diego shelter were evacuated to a stadium.

As a cold front approaches from the eastern Pacific, showers and mountain snow will move into western Washington and Oregon on Saturday, forecasters say. Colder than normal temperatures are expected to persist across much of the central and northern United States through Saturday, the National Weather Service said.