Blizzard conditions lifted across the Midwest by Wednesday afternoon, but subzero temperatures overnight will test the hundreds of thousands still without power.
In Ohio alone, more than 200,000 homes and businesses were without power as trees downed by snow, ice and wind cut power lines. In the Chicago area, some 123,000 utility customers saw their electricity cut at the height of the blizzard. Crews had reduced that to 48,000 by Wednesday evening.
In Texas, soaring electricity demand due to frigid cold forced the power grid operator to start rolling blackouts of up to an hour to one million homes.
In the Northeast, Boston saw heavy snow Tuesday followed by rain on Wednesday and then iced-over streets by nightfall.
Several building roofs in Boston and other areas collapsed due to the weight of weeks of snow, though no injuries were reported.
New York City, for its part, expected nearly an inch of ice covering its streets and sidewalks.
The monstrous storm, billed as the worst in decades, delivered knock-out after knock-out as it made its way from Texas to Maine, touching some 30 states and bringing a huge swath of the country to a halt.
Major automakers shut down plants in six Midwestern states as did hundreds of smaller employers.
The storm was, if not unprecedented, extraordinarily rare, National Weather Service meteorologist Thomas Spriggs said.
"A storm that produces a swath of 20-inch snow is really something we'd see once every 50 years — maybe," Spriggs said.
The Red Cross said it had opened more than 70 shelters across the Midwest.
Around 2,430 National Guard troops are providing winter storm support, NBC News reported.
The system was blamed for at least 10 deaths, including a homeless man who burned to death on Long Island as he tried to light cans of cooking fuel and a woman in Oklahoma City who was killed while being pulled behind a truck on a sled that hit a guard rail.
In areas where the storm had passed, a deep freeze set in.
In the Kansas City area, air temperatures in the single-digits and below were translating to wind chill temperatures of 5 below to 15 below zero degrees.
In North Dakota, wind chills were ranging Wednesday from 35 below to 55 below zero, and in Minnesota wind chill temperatures were ranging from 25 below to 35 below zero.
Overnight temperatures in the Chicago area were expected to fall to minus 5 to minus 20, with wind chills dropping to 20 to 30 below zero.
The extreme temperatures were overwhelming services for the poor and homeless in many areas.
"When you combine snow with wicked cold it brings even the toughest people in," said Dennis Chapman, associate executive director of the City Union Mission in Kansas City, which sheltered nearly 400 people Tuesday night.
He said they expect even more Wednesday night and will be putting mattresses on the floor to accommodate the crowd.
Forecasters warned ice accumulations could knock down some tree limbs and power lines across the storm's more than 2,100-mile path. Ice also could affect transit service, even as plow drivers struggled to keep up with the snow on many roads.
In New York, Mike Schumaker was already into his fourth hour of what he predicted would be a 24-hour plowing marathon as he cleared snow from a suburban Albany gas station around 5 a.m. ET Wednesday.
"I figure I'll be going to about 1 or 2 in the morning. That's my guess," said the private contractor from Latham.
"It's not so much about plowing as it is about to where to put it," he said. "We still have snow from Christmas that hasn't melted."
In Chicago, the city shut down Lake Shore Drive for the first time in years, as hundreds of motorists were stranded overnight after multiple car accidents on the iconic roadway.
On Wednesday morning, Lake Shore Drive looked like rush hour had been stopped in time. Three lanes of cars cluttered the road with snow reaching as high as the windshields. Some cars were almost completely buried.
Bulldozers worked to clear the snow from around the cars, then tow trucks plucked them out of snow drifts one by one. The operation likely would take hours: Up to 900 cars awaited rescue.
Chicago O'Hare reported 20.2 inches of snow by 10:30 a.m. ET, the third highest snowfall total in the city's recorded history after the blizzards of 1967 and 1999.
Missouri reopened Interstate 70 from Kansas City to St. Louis on Wednesday after closing it for the first time in history. The state has as much as 1.5 feet of snow.
In the Northeast, spots in northern New York had already gotten more than a foot of snow. New York City was expected to get up to three-quarters of an inch of ice by midday before the mix of sleet and freezing rain warms up to rain.
More than 5,300 flights had been canceled Wednesday as of 10 a.m. ET, or more than 16 percent of the day's scheduled traffic, according to flight-tracking service FlightAware.com. That came a day after airlines grounded 12,630 flights due to the storm.
At Chicago's O'Hare airport, airlines cancelled all flights Wednesday and probably into Thursday. That was certain to have ripple effects at other U.S. airports, said transportation expert Joseph Schwieterman.
"Effectively shutting down America's most important aviation hub hits the system immeasurably hard," he said about O'Hare.
Boston's Logan Airport was closed for a brief time as well Wednesday.
Amtrak canceled trains in the Midwest as well as service between New York City and Philadelphia.
At least two weather-related deaths were reported in New York, including a traffic fatality and a homeless man on Long Island who, police said, had burned to death as he tried to light cans of cooking fuel while sheltering behind a food market.
A 20-year-old woman died in Oklahoma City while being pulled behind a truck on a sled that hit a metal guard rail. A Michigan man died when his pickup truck rolled over several times on an icy highway and a Wisconsin man died while shoveling snow.
More than 200,000 homes and businesses in Ohio began Wednesday without power, while in excess of 100,000 customers had no electricity in New Jersey and Pennsylvania, which were hit with mostly freezing rain and ice. Rolling blackouts were in Texas, including Super Bowl host city Dallas.
As of 8 a.m. ET about 54,000 customers were without power in the Dallas-Fort Worth metro area and in parts of east and west Texas, Oncor Corp. told NBC News. The energy provider supplies about a third of Texans.
The NFL did manage to stick to its Super Bowl schedule, holding media activities at Cowboys Stadium in suburban Arlington as planned, though the city's ice-covered streets were deserted.
Federal Emergency Management Agency director Craig Fugate said the agency is on standby with generators, food, water and other supplies to help state and local authorities.
In Chicago, public schools were closed for the first time in 12 years.
The Weather Channel reported snow drifts of up to 8 feet in Lake County, north of Chicago.
Reports of more than 20 inches of snow came in from Racine, Wis.; parts of Kane County, west of Chicago; and Beach Park, Ill., NBC News said.
Kansas Gov. Sam Brownback declared a state of emergency in 53 counties, The Weather Channel said.