A major winter storm swept across the northeastern United States on Sunday after causing heavy snowfall in the central region, threatening millions of Americans with power outages and transportation paralysis due to freezing temperatures.

Many supermarkets were emptied in response to forecasts from the National Weather Service (NWS) which predicted heavy snowfall and ice accumulations with potentially "locally catastrophic" consequences from the southern plains to the Atlantic coast.

In total, 20 states as well as the US capital, Washington, have declared a state of emergency.

Approximately 14,000 flights to and from the United States were canceled over the weekend, and thousands more were delayed, according to FlightAware.

The storm, described as "unusually widespread and long-lasting" by the NWS, is caused by the arrival of an Arctic air mass from Canada.

In New York, where temperatures are expected to remain below freezing all day and up to 30 centimeters of snow is forecast for Central Park, Mayor Zohran Mamdani urged residents to avoid all non-essential travel on Sunday. A decision will be made later today regarding a possible school closure on Monday, in which case classes would be held online.

- Texas is shivering -

Snowfall was already recorded Saturday in the central United States, particularly in Kansas, Oklahoma and Missouri, where some localities showed 20 centimeters on the ground Saturday evening, the NWS indicated.

A southern city more accustomed to mild temperatures, Dallas saw the thermometer plummet to -6°C.

In Houston, shelters, particularly for the homeless, opened Saturday afternoon in this city of nearly 2.4 million inhabitants.

"Last night I stayed in my encampment in the rain, and it wasn't even really cold. But I know that tonight it would probably kill me," Caroll Eaton, a 71-year-old homeless man encountered in Houston, told AFP.

While Texas's power grid experienced a widespread outage during the last major winter storm in 2021, authorities have been reassuring about its resilience this time.

According to the website poweroutage.us , more than 180,000 homes and businesses were still without electricity Sunday morning, including some 45,000 in Texas and 67,000 in the neighboring state of Louisiana.

Donald Trump said on Saturday that he had approved emergency declarations for 12 southern and east coast states, which will allow for faster deployment of resources from FEMA, the U.S. agency for managing natural disasters.

"Stay safe and stay warm!", the US president urged again on his Truth Social platform.

- Polar vortex -

On Friday, he had anticipated the arrival of the storm to express once again his skepticism about climate change: "Could the environmental insurgents please explain to me: WHAT HAPPENED TO CLIMATE WARMING?"

The relationship between climate change and winter storms of this type, when Arctic air normally confined to the North Pole escapes towards the North American continent, is the subject of debate within the scientific community.

Researchers note that disturbances in the polar vortex, which send these Arctic air masses toward the United States, have become more frequent over the past twenty years. This could be due to the relatively rapid warming of the Arctic, which weakens the belt of winds that usually insulates the atmosphere above this polar region of North America.

But scientists are waiting for more data, over a longer period, to firmly establish a link between these extreme winter storms and climate change.

- "Five or six minutes" -

New York Governor Kathy Hochul urged residents to stay home due to the freezing cold.

"Five or six minutes outside can be literally dangerous to your health," she stressed.

Authorities have warned of extreme, potentially deadly cold that could persist for up to a week after the storm, particularly in the Northern Great Plains and Upper Midwest, where temperatures are expected to drop below -45°C.