More than 500 more flights were canceled across the U.S. on a snowy, blustery Christmas Day, many of them in Texas, where the Dallas and Houston areas were smacked with a rare coating of snow and ice Tuesday.

The travel website flightaware.com reported that 523 flights into or out of U.S. airports were scrubbed. Many were at the Dallas and Houston airports, which got rare Christmas snowfall.

NBCDFW.com: White Christmas brings delays, cancellations to DFW airport

With 8 to 15 inches of snow expected across northern Ohio on Wednesday, United Airlines canceled at least 60 percent of its flights at Cleveland Hopkins Airport beginning at noon Wednesday, NBC station WKYC of Cleveland reported.

Numerous traffic accidents also stalled motorists across Texas and Oklahoma as drivers slid and crashed in a mixture of wind, sleet and snow. Twenty-one cars and tractor-trailers crashed in a massive pileup on roads coated with freezing rain in Oklahoma City.

"You definitely have to worry about everyone while you're driving, especially out here," Dallas resident Jerdal Whitaker told NBC 5 of Dallas. "We're not used to the weather that comes, especially when it's ugly, so you definitely have to drive slow."

With temperatures expected to drop into the teens, little melting was expected overnight.

Christmas storms spread snow, tornadoes across US, snarling travel

The Midwest was also heavily hit. A blizzard was forecast to end up having dropped 10 to 15 inches of snow on parts of Indiana, where road crews began work last Friday on keeping roads as passable as possible.

"We're hoping to make it there in time before that weather hits," said James Mason, who was driving home Tuesday to Missouri with his wife and three children through Indiana.

"We don't want to get caught up in it. That is when accidents happen and people get stranded," he told NBC station WTHR of Indianapolis during a rest stop in Plainfield, Ind.

The heavy snow spread into Kentucky, where state officials urged people to stay at home and off the roads.

"Try to avoid travel from, say, 9 or 10 Tuesday night through about noon on Wednesday, simply because the conditions are going to be so brutal," said Keith Todd, a spokesman for the state Transportation Department. "If you do go out, you  need to be prepared like you're going to the North Pole."

In Ohio, the Transportation Department planned to have more than over 100 snow plows on the streets by 4 a.m. Wednesday.

The storm is forecast to hit the Northeast sometime Wednesday evening, bringing a mix of heavy sleet, snow or heavy rain, depending on its track. 

Motorists were warned to expect whiteout conditions in falling and blowing snow overnight Wednesday in the Buffalo area, where some locations could get as much as 14 inches by late Thursday, NBC station WGRZ of Buffalo reported.

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