NWS: Coldest temperatures in two decades hit two-third of U.S.[UPDATE] CHICAGO, Jan. 6 (UPI) -- A "polar vortex" thrust the eastern two-thirds of the United States into historically frigid conditions. Even the southernmost states had wind-chill warnings. "The coldest temperatures in almost two decades" spread into the northern and central parts of the country, packing gusty winds that produced "life-threatening wind-chill values as low as 60 degrees below zero," the National Weather Service said. The extreme temperatures and blustery winds produced by the arctic cyclone created dangerously cold wind chills as far south as cenral Florida and Brownsville, Texas, the weather service said. Weather Channel meteorologist Kevin Roth said the low temperatures were caused by a "polar vortex" moving down from the arctic. Temperatures may be so cold in some places water mains could burst, weather service meteorologist Bob Oravec told the Wall Street Journal. Poor visibility from blowing snow trapped the Southern Illinois University men's basketball team, returning home from a 66-48 loss to Illinois State, on the side of Interstate 57 late Sunday, SIU Athletic Director Mario Moccia said. The bus driver pulled off the highway to get out of the way of traffic until visibility improved, but when the driver tried to get back on the road, the bus had no traction and was stuck, CNN reported. "They're just hanging out, they're watching movies," Moccia told CNN late Sunday night. He said the bus had plenty of fuel, heat and food, and the team was waiting for a tow truck. Players later tweeted they would be spending the night in a church in Tuscola, Ill. Somehow this eventful day/night has led to our team sleeping on the floor of a church in Tuscola. What a journey it has been," Dawson Verhines tweeted. Hundreds of school districts, from North Dakota, Minnesota and Wisconsin east to Ohio and as far south as northern Texas, were closed Monday because of the brutal cold. "This is shaping up to be one of the worst winter storms in Indiana history," DePauw public safety Director Angie Nally said on the university website. More than 1,900 flights were canceled as of early Monday, including almost half the flights at Chicago's O'Hare International Airport and more than half at Cleveland Hopkins, said flight-tracking website FlightAware.com, which monitors cancellations due to weather, and mechanical and other problems. About 3,700 flights were canceled Sunday, leading to disruptions at scores of airports, including Philadelphia, Indianapolis, St. Louis, Detroit, Newark, N.J., and New York's Kennedy International Airport. In Racine, Wis., officials closed the Racine Zoo Monday to protect animals as well as guests and staff, officials said. Zoos in Duluth and Apple Valley, Minn., also were closed because of the extreme cold. Snow preceded the arctic air, dropping a foot or more in some areas of Michigan, Illinois and Missouri in the Midwest and several inches in Kentucky and Tennessee in the east south-central region.