U.S. grapples with sprawling winter storm system

(Reuters) - A major winter storm on Tuesday made its way across the heart of the United States, bringing heavy snows and strong winds to the Northern Plains and the potential for tornados and flooding to the South.

Severe weather was expected on Tuesday across a huge swath of the country, with tornado, blizzard and flood warnings dotting the National Weather Service's main map.

"This storm system will continue to produce numerous, widespread, and impactful weather hazards from the Rockies to the East Coast," the service said in its forecast.

The nasty weather was at least partly to blame for delaying more than 310 flights and canceled another 30 across the nation early on Tuesday morning, Flightaware.com reported on its Misery Map.

It also forced school districts to cancel classes in the Dakotas, Colorado and Nebraska where blizzard-like conditions were reported. Some spots in the four-state area were expecting two feet (61 cm) of snow and winds of 60 miles (97 km) per hour throughout the next two days, the NWS said.

Blowing snow and ice accumulation forced the closure of many highways and roadways throughout the area, transportation officials said on social media, urging motorists to stay home.

"Be aware of rapidly changing conditions. Reduce speeds and drive according to the conditions," the North Dakota Department of Transportation said in a Tweet.

Forecasters warned that temperatures across the area could drop as low as minus 20 Fahrenheit (minus 29 degrees Celsius), a level that causes frostbite on exposed skin within 30 minutes.

The wintry mix of precipitation will spread from the Upper Great Lakes on Tuesday into the Northeast late on Wednesday bringing with it the possibility of as much as 8 inches (20 cm) of snow to some spots.

To the south in Dallas–Fort Worth region, at least one tornado was reported on Tuesday morning by the NWS, which warned of potential dangerous twisters and strong thunderstorms throughout the day.

"TAKE COVER NOW! If you are outdoors, in a mobile home, or in a vehicle, move to the closest substantial shelter now!" it said in an alert at 8:15 a.m. local time.

The storm was also expected to produce heavy downpours in the deep South that cause flash flooding in Louisiana and Mississippi, the service warned.