A monster winter storm stretching from New Mexico to Maine laid down a sheet of ice on the Plains and lower Midwest on Tuesday, turning to snow as it crept north, and forecasters said the worst was yet to come.

"We're looking at heavy snow from the Rockies to New England," said Pat Slattery, National Weather Service spokesman.

The storm was expected to affect as much as a third of the U.S. population, from severe thunderstorms in the Southeast and ice-coated roads in Texas to blizzard conditions and up to 2 feet of snow in Chicago. Several regions were experiencing bitter cold, including Denver, where mid-afternoon readings fell to six degrees below zero.

In Oklahoma City, more accustomed to tornadoes than blizzards, homeowner Debra Thomas, 53, said the entire town was largely snowbound as gale-force wind gusts and a foot of snowfall created white-out conditions and large drifts.

"I'm looking out my door here, and I've got at least 4 feet, maybe 5 feet, up against the windows of our house," she told Reuters by telephone. "It's very pretty, but not the kind of thing you go out in."

The Dallas-Fort Worth international airport closed for 2 1/2 hours on Tuesday just as thousands of football fans began arriving in the city for the Super Bowl game on Sunday. And the storm forced postponement of a National Hockey League game in St. Louis between the Blues and the Colorado Avalanche.

About 200 National Guard troops were called out to assist local law enforcement in the St. Louis area.

Major U.S. airlines said they had canceled more than 5,400 flights ahead of the storm. More than 1,200 of those flights were in and out of Chicago-area airports, major airline hubs.

One of the hardest-hit cities on Tuesday was Kansas City, where a municipal state of emergency was declared and snow plows were pulled from runways at the international airport in late afternoon due to blowing snow and low visibility.

Statewide emergencies were declared in Missouri, Oklahoma, Illinois and Wisconsin. White-out conditions were reported on Interstate 44 between Oklahoma and Missouri, closing part of that highway, as well as Interstate 70 in central Missouri.

"Everyone should stay inside today and not drive," Missouri Governor Jay Nixon said on local television.

Weather Service meteorologist David Gaede said: "There's not much traffic moving in Missouri tonight."

"Black ice" conditions prompted Nebraska state police to shut down Interstate 80 and I-680 in Omaha at the start of the evening rush hour.

Storm-related outages knocked out power to more than 100,000 homes and businesses in at least eight states, including Texas, Louisiana, Arkansas, Missouri, Kentucky, Indiana, Illinois and Ohio.
Once the snow lets up Wednesday, affected areas will remain stuck in a deep freeze through the end of the week, with single digit temperatures in the daytime and "really dangerous wind chills," Slattery said.

Schools were closed all along the storm's path, from Denver through Ohio. Chicago public schools, famous for staying open no matter the weather, stayed open Tuesday but were ordered closed on Wednesday.

The snow began coming down hard in Chicago by 2:30 p.m. In the morning, residents were already setting out lawn chairs and plastic buckets to stake out parking spots in advance of the storm. The city readied all 274 of its snow plows for service, along with 120 garbage trucks fitted with plow attachments.

The National Weather Service said Chicago could get its biggest blizzard in more than 40 years, accompanied by winds of more than 40 miles per hour and plunging temperatures.

At the CME Group's downtown trading floor in Chicago, many traders who buy and sell agricultural commodities, financial contracts and options were planning to stay downtown overnight, storing suitcases in the coat room. But trading was not expected to be affected.

Bob Margherio, owner of Mac Do It Best Hardware in Webster Groves, Missouri, said he had run out of ice-melt spread, snow blowers, generators, and flashlights and had nearly exhausted his inventory of batteries.

In New York City, forecasters said the wintry mix of snow, sleet and freezing rain would last into Wednesday as the storm moved in from the Midwest.

"It's far from a picturesque scene. It's an icy, wet mess," said meteorologist John Davitt of local NY1 television.

The storm was expected to wreak havoc on farm operations in the Plains states, threatening the dormant winter wheat crop, cattle herds, and grain deliveries.