At least 13 traffic deaths are now being blamed in icy conditions in the southern Plains and in the Midwest.
At least 12 deaths have been reported in Oklahoma, where thousands are without power and airline flights are being canceled.
Another death was reported in Missouri.
Yesterday in Oklahoma, ice accumulations were already being reported at a half-inch thick, and forecasters say it could build up to as much as an inch thick in the Oklahoma City metropolitan area.
Most morning flights were canceled at Oklahoma City's Will Rogers World Airport, where two of the three runways were iced over.
Tens of thousands of customers also remain without power in Missouri.