As of Wednesday, about 75 million people in 28 states have been placed under winter weather alerts.
Blizzards in the Dakotas, Minnesota and Wisconsin have forced many schools and businesses to close.
Meanwhile, high temperatures in Washington DC are expected to break a nearly 150-year-old record.
Record low temperatures in the US
Powerful wind gusts potentially reaching 50mph (80km/h) and a wind chill as low as -50F in some parts are predicted.
In northern states, forecasts of up to 2ft (60cm) of snow in some parts could mean areas endure their biggest snowfalls for 30 years.
Minnesota’s governor Tim Walz said the National Guard will be available to help motorists who become stuck in the blizzard conditions there. The state may break its record for snowfall, officials said.
Forecasters said the storm system could span 1,300 miles from Nebraska to New Hampshire.
More than 1,700 flights have been cancelled in the US as a result of the storm.
Icy weather is also forecast for typically sunny and warm Los Angeles, California, where a rare blizzard warning has been issued. Major snow and winds up to 75mph are forecast in the mountains and foothills of Ventura and Los Angeles County.
All of California’s 39 million residents will be able to see snow either falling around them or settling at the tops of nearby mountains, said Daniel Swain, a climate scientist at the University of California-Los Angeles.
As of Wednesday night, frigid temperatures of -9F have been recorded in parts of Montana.
Record high temperatures in the US, too
Meanwhile, much of the southern US is basking in unusually high temperatures for this time of year. On Wednesday, McAllen, Texas, recorded a sweltering 95F.
The heat on Wednesday in Lexington, Kentucky, and Nashville, Tennessee, shattered records stretching back more than a century.
Cincinnati, Indianapolis, Atlanta and other US cities also saw record highs.
Washington DC could hit 80F on Thursday, which would break a record set in 1874.
Orlando, Florida, could hit 90F and New Orleans, Louisiana, could notch 84F.
“All winter, we’ve seen this persistent pattern, where the western US is seeing below-average temperatures and the eastern US is seeing above-average temperatures,” climate scientist Andrew Kruczkiewicz, a researcher at Columbia University, told BBC News.
Canada is also feeling effects of the winter storm
Large parts of the country are under weather alerts, including Toronto, which is expecting 4-10in (10-15cm) of snow, ice pellets and possible freezing rain.
The winter storm has also halted flights. Air Canada had cancelled about a quarter of its scheduled flights by Wednesday afternoon.
The country just had record-breaking warm temperatures for February. Now, parts of Toronto could see significant ice build-up as a result of this recent cold snap.
Parts of Alberta and the prairies are facing extreme cold warnings, with temperatures dropping in some regions into the -40F (-40C) range with wind chill.
Source: BBC