The icy weather was expected to make roads hazardous through at least Monday from the upper Midwest to northern New England during one of the busiest travel times of the year.
As of midafternoon, more than 700 airline flights had been canceled and more than 11,000 delayed, according to aviation tracking website FlightAware.com.
High-temperature records for the date fell for the second straight day in the mid-Atlantic states because of a mass of hot, muggy air from the South.
In New York's Central Park, the mercury reached 70 degrees, easily eclipsing the previous high of 63 from 1998. Records were also set in Wilmington, Del., (67), Atlantic City, N.J., (68), and Philadelphia (67). Washington, D.C., tied its 1889 mark at 72.
Temperatures were expected to return to normal by Monday night and Tuesday, dropping back into the 30s.
The scene was much more seasonal Sunday in Vermont, where Lynne White of West Charleston listened to the cracking of falling tree branches and gazed at the coating of ice on her home.
"It's actually really pretty," she said. "Not safe, I'm sure, but it's pretty."
Heavy snow in Wisconsin forced dozens of churches to cancel Sunday services. Milwaukee got about 9 inches, Manitowoc 7. Ice and snow in Oklahoma were blamed for three traffic deaths on slick roads.
In New York's St. Lawrence County, almost 2 inches of ice had accumulated by early Sunday, coating tree limbs and power lines, and a state of emergency was declared to keep the roads clear of motorists.
"It's a big party weekend ... before Christmas," county dispatch operations supervisor Jim Chestnut said. "This put a little bit of a damper onto that."
Despite a glaze of freezing rain in Maine, plenty of shoppers ventured to the outlet malls in Kittery, Maine, on the last weekend before Christmas.
In Canada, crews struggled to restore service to those without power in Ontario, Quebec and New Brunswick. Toronto Mayor Rob Ford called the storm one of the worst in the city's history. Passengers were stranded at airports from Toronto to St. John's, Newfoundland.
In Kentucky, five people were killed in flooding caused by the storm system. The bodies of three people were pulled from Rolling Fork River on Sunday after their vehicle was swept away by floodwaters, a fourth person drowned in Carroll County after a four-wheeler overturned in high water, and a body was discovered in Ballard County near a car abandoned in a flooded ditch.
In Arkansas, authorities said Sunday that a woman was killed after an EF2 tornado with winds of about 130 mph struck in St. Francis County on Saturday. A man found in a field was hospitalized in serious condition, while the woman's 3-year-old granddaughter and 25-year-old daughter were treated at a hospital.
Associated Press writers Mary Esch in Albany, N.Y., Bruce Shipkowski in Trenton, N.J., Ken Miller in Oklahoma City, David Goodman in Detroit, Rick Callahan in Indianapolis and Steve Karnowski in Minneapolis contributed to this report.