The northeastern United States and Canada steeled themselves for an "epic" Arctic blast that could see some areas record their lowest-ever wind chill temperatures.
America's National Weather Service (NWS) warned that parts of Maine might see wind chills of minus 60 degrees Fahrenheit (minus 51 degrees Celsius).
"This is an epic, generational arctic outbreak," the NWS office in Caribou, near Maine´s border with Canada, wrote in an advisory.
It said the chills are "something northern and eastern Maine has not seen since similar outbreaks in 1982 and 1988."
"Most stations are forecast to see their lowest wind chills in decades or, in some cases, the lowest ever recorded," the service added.
It warned that frostbite to exposed skin can occur within five minutes in such conditions.
"The dangers of being caught unprepared without shelter from the elements and without proper winter survival gear cannot be stressed enough," the service wrote.
The most extreme conditions are forecast to occur Friday night into Saturday morning, with extreme weather warnings in effect across Quebec and much of eastern Canada.
In Montreal, the wind made the temperature feel like minus 41°C early Friday afternoon.
The mercury was predicted to drop as low as minus 50°C in the northern regions of Quebec because of the strong, cold gusts.
White Arctic sea smoke rose over parts of the St. Lawrence River due to extreme cold winds passing over the unfrozen water.
The Hydro-Quebec power company said it was preparing for a historic consumption of electricity overnight Friday to Saturday and called on users to reduce their use.
In the Canadian capital Ottawa, a snow squall — snowfall combined with 60-70 kilometre per hour winds — overnight Thursday to Friday reduced visibility to near zero.
On the streets downtown, the few residents who ventured out wrapped themselves in wool blankets atop their parkas.
Wind chill warnings were also in place across much of New England.
Boston, where public schools were closed Friday, and surrounding areas are expected to receive a wind chill of minus 34°C.
Further south, New York City is forecast to be minus 23°C, according to the NWS.
Warmer air is due to move into the region early Sunday.
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