Parts of the US are experiencing a record-breaking wind chill factor that is so cold it's literally off the National Weather Service's official charts.
The northeast of the country has been struck by a powerful arctic blast, with the temperature at New Hampshire's Mount Washington plummeting to a new low of -46F (-43C).
But the wind chill temperature is how cold people actually feel while outside and depend on the strength and temperature of winds.
High winds of 96mph on Mt Washington have produced a wind chill factor of -108F (-78C) - comfortably below the lowest point on the National Weather Service's (NWS) wind chill chart, which stands at -98F (-72C).
'Worst weather in the world'
NWS said Mt Washington, the highest peak in the northeastern US, was "living up to the reputation of having the worst weather in the world".
New Hampshire is one of several states under wind chill warnings, alongside Massachusetts, Connecticut, Maine, Rhode Island, Vermont, and much of New York, where a "Code Blue" alert for sub-zero temperatures was issued.
Thousands of properties have lost power and emergency shelters have been opened.
While the deep freeze is expected to be relatively brief, people are being warned the conditions are life-threatening, with schools closed in some cities due to risks of children suffering hypothermia and frostbite.
One weather expert says the wind chills forecast could cause frostbite on exposed skin in just 10 minutes.
Meteorologist Donald Dumont at the National Weather Service in Gray, Maine, said: "It's painful."
One of the cities hit by the worst of the freeze is Boston, Massachusetts, where mayor Michelle Wu declared a state of emergency.
Record low temperatures are forecast there for Saturday, and in one of the state's other cities, Worcester, where residents have already endured lows of 3F (-16C) heading into the weekend.
Boston's record low is -2F (-19C), set back in 1886, and Worcester's is -4F (-20C), which dates back to 1934.
'Citizens have been let down'
The freezing conditions, which are sweeping in from eastern Canada, come as southern states recover from another winter storm that brought days of rain, sleet, and ice.
In Texas, thousands of residents were still without power on Friday night, even as conditions warm up. One of the state's biggest cities, Austin, has seen 30% of customers without electricity at any given time since Monday.
Mayor Kirk Watson admitted the city "let its citizens down".
"The situation is unacceptable to the community, and it's unacceptable to me," said the Democrat.
One resident, Edward Kim, has had no power or heat since Wednesday. The 43-year-old revealed he was using a generator to keep his home "on life support".
Another local, Will Rison, said his elderly parents had also been without electricity for three days.
"You can only wrap yourself in so many blankets and wait it out," he added.
While no deaths have been reported as a result of the outages, the weather has been blamed for at least a dozen deaths on roads across Texas, Arkansas, and Oklahoma this week.