President Trump has approved emergency declarations in 10 states as a life-threatening storm bears down on about 140 million Americans.
Snow, ice and freezing temperatures are forecast from the Rocky Mountains and New Mexico all the way to the east coast.
Frostbite in minutes is possible in parts of Minnesota and North Dakota, where wind chill temperatures as low as -46C (-50F) are possible.
About 140 million people - more than 40% of the US population - are under a variety of weather warnings and more than 8,000 flights have been cancelled.
President Trump said on Saturday he had approved emergency declarations in 10 states and urged people to "Stay Safe, and Stay Warm!"
Where is it heading?
The National Weather Service - which said the storm is "life threatening" due to the risk of hypothermia and frostbite - has warned of "widespread heavy snow, sleet and freezing rain from the Southern Rockies to New England" until Monday.
"Crippling to locally catastrophic impacts can be expected" from the Southern Plains to the Mid-Atlantic/Southeast, according to the NWS.
Communities in the firing line have been urged to prepare for "bitterly cold temperatures and dangerously cold wind chills".
The storm is expected to bring an ice storm from Texas through parts of the South, potentially around 30cm (12ins) of snow from Oklahoma through Washington DC, New York and Boston.
Then a final punch of bitterly cold air could plunge wind chill temperatures to -46C (-50F) across the Northern Plains.
Forecasters are warning the damage could rival a hurricane in some areas.
"The storm will cause significant to locally catastrophic ice accumulations with the potential for long-duration power outages, extensive tree damage, and extremely dangerous or impassable travel conditions," the NWS said.
Millions braced for 'catastrophic' winter storm
Weather alerts stretch from Arizona and Montana in the West to the Carolinas and Maine in the East, with a total of 12 states now declaring states of emergency.
These include Texas, Georgia, South Carolina, North Carolina, Virginia, Maryland, Louisiana, Arkansas, Tennessee, Alabama, Mississippi and Missouri.
What has the federal response been?
The Federal Emergency Management Agency (FEMA) has pre-positioned supplies and is deploying more than 200 call centre specialists, according to Sky's US partner NBC News.
Thirty search and rescue teams are also on standby.
Seven million meals, 600,000 blankets and 300 generators are also ready in areas expected to worst hit, officials said.
President Trump said on Truth Social on Saturday: "We are working closely with FEMA, Governors, and State Emergency Management teams to ensure the safety of everybody. Stay Safe, and Stay Warm!"
What have people been told to do?
Residents have been advised to stay at home and off the roads and to prepare by stocking up on food and drink supplies.
"Items like flashlights, batteries, and battery back-ups can make all the difference," the North Carolina Department of Emergency Management said in a social media post.
Items including mobile phone chargers, radios, winter clothing, blankets and a first-aid kit should also be added to emergency kits.
It warned people should never run a generator inside a house or garage to avoid carbon monoxide poisoning.
The NWS also reminded people to protect pets and animals from the cold.
The Georgia Emergency Management Agency said people should regularly check the forecast for any changes and gather supplies for homes and cars, check smoke and carbon monoxide detectors, and refuel cars and heating sources.
It also said people should check in on neighbours and family, properly ventilate emergency heat sources, keep generators 20ft from homes and to be careful while shovelling snow and ice.
(c) Sky News 2026: 'Life-threatening' winter storm to hit US with snow, ice and 'dangerously' cold temperatures
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