Ice storms occur when rain falls in temperatures so low it freezes
About 30 people have now been killed in ice storms that have struck the US, mainly in central states.
A state of emergency has been declared and the National Guard called out in Missouri after the storms knocked out power to 200,000 homes.
President George W Bush has released federal aid for some affected states.
Weather forecasters say the storm system will head north-east, threatening to bring more than a foot (30cm) of snow to New England.
Ice storms occur when rain falls during very low temperatures, causing it to freeze almost instantly as it hits a surface, resulting in ice layers sometimes several inches thick.
The extreme weather downed trees, traffic lights and power lines and blocked roads in Missouri and Oklahoma, where most of the deaths occurred.
Other fatalities were in Iowa, Texas, New York and Maine.
President Bush declared an emergency in Oklahoma.
There, about 350 national guardsmen went door-to-door to check on residents in the hardest-hit areas, and helped to clear icy roads of branches and power lines.
In Texas, 415 flights were cancelled on Sunday at Dallas-Fort Worth International Airport.
Record-breaking cold weather even hit California, which usually has mild temperatures year-round.
Citrus fruit growers in parts of the state are using wind machines to protect their fruit from frost damage.
The National Weather Service said it was "a very, very big cold front".
It said the storm is gathering moisture from the Gulf of Mexico and cold air from the Arctic, and is expected to hit the east coast on tuesday.