NEW York, United States (AFP) — Millions of Americans were facing dangerously cold temperatures Monday in the wake of a massive winter storm that whipped snow and ice across the country, knocking out power and paralysing transportation.

A frigid, potentially life-threatening Arctic air mass threatened to delay clean-up as municipalities from New Mexico to Maine tried to dig out following the storm, which dropped a vicious cocktail of heavy snow and wind along with freezing rain and sleet.

Over 780,000 customers remained without electricity late Monday afternoon, the Poweroutage.com tracking site showed.

Tennessee, Texas, Mississippi, and Louisiana — southern states unaccustomed to intense winter weather and the bone-chilling cold that’s forecast to continue for much of the next week — were especially impacted.

Approximately 190 million people in the United States were under some form of extreme cold alert, the National Weather Service (NWS) told AFP.

Areas across 20 states received at least a foot of snow (30.5 cm), and in many cases far more. The NWS said New Mexico’s Bonito Lake accumulated the highest US total over the weekend with 31 inches (78.7 cm).

New York’s Central Park received 11.4 inches (29 cm) — breaking a same-day snowfall record from 1905.

A compilation of local media reports tallied at least 21 storm-related deaths.

NWS meteorologist Allison Santorelli told AFP the agency was seeing widespread reports of significant ice accumulation, including in places unaccustomed to severe winter weather.

She said this storm recovery was particularly challenging because so many states were impacted — meaning northern states with more resources were unable to share their equipment and resources with less-prepared southern areas.

“A lot of those locations don’t have the means or the resources to clean up after these events,” she said. “We’re particularly concerned about the folks in those areas that are without power right now.”

Dave Radell, an NWS meteorologist based in New York, told AFP that the character of this storm’s snow was “very dry” and “fluffy”, meaning the wind could lash it around with ease, impeding road-clearing efforts and visibility.

“That makes it even more challenging,” he said.

The snowfall and biting icy pellets that pummelled cities saw impassable roads, cancelled buses and trains along with grounded flights — thousands of departures and arrivals were scrapped over the weekend — as concern turned to the hazardous temperatures set to linger for the better part of a week.

The brutal storm system was the result of a stretched polar vortex, an Arctic region of cold, low-pressure air that normally forms a relatively compact, circular system but sometimes morphs into a more oval shape, sending cold air pouring across North America.

Scientists say the increasing frequency of such disruptions may be linked to climate change, though the debate is not settled and natural variability plays a role.

At least 20 states and the US capital Washington were under states of emergency in order to deploy emergency personnel and resources.

Many cities had opened warming centres for those without shelter or without power to take refuge, and authorities across the country were continuing to encourage residents who could to stay home.