More than 100 million people are under winter weather alerts across the United States.
That includes 11 million living with blizzard warnings across eight states.
The country is braced for a "bomb cyclone" of heavy snow, rapidly plunging temperatures and life-threatening wind chills.
Temperatures could fall to minus 40 degrees celsius in some parts - including the northern Rockies.
Thousands of flights have been cancelled in the US as a huge winter storm sweeping the country disrupts holiday travel.