(BSS/AFP) - Americans stripped supermarket shelves Friday ahead of potentially "catastrophic" winter weather that threatened at least 160 million people across the country with transportation chaos, blackouts and life-threatening cold.

The massive storm system was set to drop a mix of freezing rain and heavy snow starting Friday evening on its days-long march across the continental US.

The storm could bring "catastrophic ice accumulation," the National Weather Service said, potentially causing "long-duration power outages, extensive tree damage, and extremely dangerous or impassable travel conditions," including in many states less accustomed to intense winter weather.

After battering the country`s southwest and central areas, the storm system was expected to hit the heavily populated mid-Atlantic and northeastern states -- stretching from New Mexico to the Eastern seaboard -- before a frigid air mass settles in.

More than 2,700 weekend flights have already been cancelled, according to the tracker Flightaware, including many in and outbound from Texas.

State officials there vow the grid is in better shape than it was five years ago, when it failed during a deadly winter storm and left millions without power.

The southern state`s Republican Governor Greg Abbott told journalists the grid "has never been stronger, never been more prepared and is fully capable of handling this winter storm."

Yet Michael Webber, a University of Texas engineering professor, warned ice accumulations would remain "a big risk" across the country -- ice could amass and weigh down trees, for example, downing power lines and provoking outages.

- Frostbite risk -

In New York state, Democratic Governor Kathy Hochul warned residents to stay inside amid frigid conditions: "Five or six minutes outside could literally be dangerous for your health."

She stressed precautions like protecting pipes, using heaters safely, and checking on vulnerable neighbors.

New York`s Zohran Mamdani was set to face his first major test as mayor -- the city famously makes early judgments of newly elected leaders based on winter storm response.

Democrat Mamdani said remote learning Monday was an option but he was not planning to close schools -- even as one student emailed his wife and urged a snow day.

School districts elsewhere were preemptively announcing closures. A professional basketball game on Saturday and dozens of collegiate games were rescheduled.

Even in Chicago, a city all-too-familiar with bone-chilling weather, an organization canceled their annual event that sees participants plunge into glacial Lake Michigan for charity (the after-party at a bar was still on.)

Authorities warned of life-threatening cold that could last a week post-storm, especially in the Northern Plains and Upper Midwest, where wind chill lows were forecast to dip to extremes under -50F (-46.6C).

Such temperatures can cause frostbite within minutes. One Minnesota television station showed uncensored photos of the serious injury that freezes skin tissues as a warning.

- Polar vortex -

The brutal storm system is 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 spilling across North America.

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

But President Donald Trump -- who scoffs at climate change science and has rolled back green energy policies -- questioned how the cold front fit into broader climate shifts.

"WHATEVER HAPPENED TO GLOBAL WARMING???," the Republican leader posted on Truth Social.

State officials were more focused on the immediate threats the powerful storm posed.

At least 16 states and Washington DC declared states of emergency to mobilize disaster response crews and resources, and many municipalities were opening warming shelters.

Lines snaked out of grocery stores where stock began running thin.

North of Houston, one supermarket was nearly out of bottled water.

Anne Schultz said preparation was key but she wasn`t particularly afraid: "If the power stays on, we should all be fine," the 68-year-old told AFP.

The Greensboro Police Department in North Carolina meanwhile warned residents to choose wisely when hunkering down.

"Please remember that whoever you hang out with on Saturday, you`re stuck with until at least Tuesday when the ice melts," the department quipped on X.