A potentially deadly winter storm is moving eastward, covering at least one-third of the country, and bringing with it a combination of heavy snow, ice, high winds and freezing temperatures.
Some forecasters said it could be the worst snowstorm the country has seen in more than 40 years. More than a foot of snow may fall on a 2,100-mile stretch from New Mexico to Maine. The National Weather Service even warned that high winds on Lake Michigan could produce waves of 25 feet, leading to coastal flooding, particularly along Chicago's Lake Shore Drive.
The storm has already snarled air traffic in Chicago and Dallas, the site of Sunday's Super Bowl. American Airlines cancelled 600 flights out of Chicago and another 900 flights at Dallas Fort Worth International Airport. According to Flightaware.com, more than 6,300 flights have been cancelled nationwide so far, with the number expected to increase as the storm moves east.
Blizzard warnings are in effect for nine states with the storm expected especially to affect Oklahoma City, Kansas City, St. Louis, Detroit, Des Moines, , Chicago and Milwaukee.
In Tulsa, Okla., the Tulsa World has announced Wednesday's paper will not be printed because of the storm, though the online edition will continue.
"This will be the first time in our history that we have not printed a Tulsa World," said publisher Robert E. Lorton III. "However, we wanted to make sure our employees and their families remained safe as we all try to deal with this weather."
Federal Emergency Management Agency Administrator Craig Fugate said the snowstorm will be powerful, and warned residents to be prepared.
"This is not something that's sneaking up on us," he said. "It's been well-forecasted. We know it's going to be bad and prepare like it's bad."
Governor Pat Quinn of Illinois activated more than 500 National Guard troops to assist motorists on several highways. The troops will be stationed at rest stops, and work with the Illinois State Police to ensure the safety of any stranded travelers.
This winter weather comes on the heels of an upper-level storm system, according to the National Weather Service.
Besides snow, rain will create icy conditions stretching from southern Missouri, across central Illinois, through Indiana and Ohio and into western Pennsylvania.
Below-zero temperatures are possible from the Dakotas to Denver, with the wind-chill reaching to as low as 40 below zero in the Great Plains.
In the Midwest and Great Plains, residents are bracing for today's weather conditions, the second system to pass through the region since Sunday.
The first system slammed into the Midwest Sunday night, dropping a foot of snow in Minnesota by Monday.
Forecasters predict up to an inch of ice, along with 3 to 4 inches of sleet and possibly more snow.
In St. Louis, forecasters expected light freezing drizzle overnight with snow to blanket the central and northeastern part of the state.
In Wisconsin, extreme snow is expected with snow showers continuing into Wednesday afternoon.
But forecasters said Chicago would bear the brunt of the storm. The city could receive up to 2 feet of snow. Parts of northern Indiana could receive nearly 3 feet.
Chicago forecasters predict the storm will rank as one of the top snowstorms to hit the city.
The last major snowstorm there was in 1999, dumping about 19 inches. In 1967, 23 inches were dumped on the city.
While the Northeast is no stranger to snow, this storm will be the seventh storm to hit the region in the past 35 days. The string started with the Dec. 26 blizzard that left the region's transportation systems crippled.
New York got snow and some light freezing rain this morning with heavy sleet later tonight into Wednesday.
Last week's snowstorm broke a record in New York City – pushing the monthly total to more than 50 inches -- the snowiest January in more than a century. The average snow total for New York is about 21 inches.
People in the Washington D.C. area are worried about today's storm too.
At Ann Simmons Knight's home in Silver Spring, Md., the power has just been restored after last week's storm, but she's worried about today's forecast of snow, sleet and ice.
"You worry about no power. You worry about trees coming down," Knight told ABC News Radio. "You worry about emergency vehicles not being able to get in because of trees across the road."
North of Philadelphia into Connecticut, a winter storm warning is in place for significant ice accumulation.
As the storm headed east, it left in its wake mangled cars caught in weather-related accidents.
A bus full of students flipped over on an icy narrow lane in Kansas City.
In Colorado, emergency crews were dispatched to help motorists who lost control and tumbled off a highway.
Crews in Oklahoma report "blizzard-like" conditions on the roads, with stalled vehicles all around the state. Transportation departments in Missouri and Illinois have interactive highway maps showing the current road conditions and closures.
ABC News' Sam Champion and the Associated Press contributed to this report.