"Swaths of half an inch of ice will be possible" over the next three days for areas from Texas to MS and up through Virginia, according to the National Weather Service.
At least two dozen people have died in the extreme weather this week, some while struggling to find warmth inside their homes. This is a weather pattern that usually keeps to the arctic but is increasingly visiting lower latitudes and staying beyond its welcome.
Scientists say global warming caused by humans is partly responsible for making its southward escapes longer and more frequent.
More than 100 million people live in areas covered by some type of winter weather warning, watch or advisory on Wednesday as yet another winter storm hits Texas and parts of the Southern Plains, the National Weather Service said.
Single-digit temperatures created a surge in demand for electricity to warm up homes unaccustomed to such extreme lows, buckling the state's power grid and causing widespread blackouts.
The weather has threatened to affect the nation's Covid-19 vaccination effort, with President Joe Biden's administration saying delays in vaccine shipments and deliveries were likely.
Texas saw the worst of the USA power outages, which affected more than 2 million homes and businesses. The state opened 35 shelters to more than 1,000 occupants, the agency said.
Vice President Kamala Harris addressed those who had lost power during a live interview Wednesday on NBC's "Today".
The situation in Texas drew attention at Wednesday's International Energy Forum, including messages of support from Saudi Arabia's energy minister and OPEC Secretary General Mohammed Barkindo.
"As the extreme weather in Texas has shown, we can not take energy security for granted, even in a country like the United States", Barkindo said at the forum, which was held virtually.
Travel remains ill-advised in much of the United States, with roadways treacherous and thousands of flights canceled. Some of the fatalities involve people dying in their cars in subfreezing temperatures. Many school systems delayed or canceled face-to-face classes.
But even staying at home can be hazardous in places without power.
Police in Houston say a woman and child died of carbon monoxide poisoning after they sat in a auto running in their garage, and authorities in Sugar Land said a grandmother and three children trying to heat their home died in a fire. In Oregon, authorities confirmed Tuesday that four people died in the Portland area of carbon monoxide poisoning.
For the second time this week, a strong storm system rolling across the South is bringing a significant dose of snow, sleet, and freezing rain from Texas to New England.
At least 13 children were treated for carbon monoxide poisoning at Cook Children's Medical Center in Fort Worth and one parent died of the toxic fumes, hospital officials said. Officials did not know when power would be restored, but ERCOT President Bill Magness said he hoped many customers would see at least partial service restored by later Wednesday or Thursday.