-- More than 1,000 flights into and out of Dallas/Fort Worth International Airport have been canceled today because of freezing rain, sleet and sub-freezing temperatures.
Meanwhile, Arctic air is returning to the Northeast, with chilling temperatures expected later today from Boston to Washington, D.C., following a milder Sunday reprieve.
At least 15 states from North Dakota to Maryland are under a wind chill advisory today. Wind chills in parts of the Midwest could drop to -40 degrees. Wind chill figures in the inland Northeast Tuesday could fall to similar figures -- near -35 degrees.
One wave of the system moved through the deep south Sunday, producing multiple accidents and spin-offs in Texas and leading authorities at Dallas/Fort Worth International Airport and airlines to take extra precautions. A second round of freezing precipitation is expected in the Dallas area during the morning rush hour, with dangerous travel conditions expected.
In Colorado, people used cross-country skis, sleds and snowshoes as more than 2 feet of snow fell.
The Associated Press contributed to this report.