Tens of millions of Americans are bracing for a massive winter storm that could bring the heaviest snowfall and coldest temperatures in more than a decade.

The storm, which began in the central United States, will move east over the next few days, the National Weather Service (NWS) said.

A state of emergency has been declared in the states of Kentucky and Virginia Parts of the U.S. not used to severe cold, including Mississippi and Florida, have been warned of treacherous conditions.

Forecasters believe the extreme weather is caused by the polar vortex, an area of ​​cold air circulating around the Arctic.

“For some, this could be the heaviest snowfall in over a decade,” the National Oceanic and Atmospheric Administration said.

AccuWeather forecaster Dan DePodwin said, “This could result in the coldest January for the U.S. since 2011.”

He added that “temperatures well below historical averages” could persist for a week.

These low temperatures will also prevail on the East Coast, where the storm is expected to arrive on Sunday evening.

The central U.S. will experience “significant disruption to daily life” and “dangerous or impossible driving conditions and widespread closures” through Sunday, according to the NWS.

Some areas of Kansas and Indiana could see at least 8 inches of snow.

Blizzards are possible in parts of the Midwest.

“Whiteout conditions make travel extremely dangerous, with roads impassable and a high risk of motorists becoming stuck,” the NWS warned.

Sleet and freezing rain are forecast for Missouri, Illinois and much of Kentucky and West Virginia.

As the storm moves east, millions more Americans will experience record temperatures, forecasters said.

Cities like Washington DC, Baltimore and Philadelphia are preparing for snow and ice Sunday through Monday. Parts of Virginia recorded 5 to 12 inches of snowfall.

Severe thunderstorms are also possible on Sunday in parts of the southern United States, including Arkansas, Louisiana and Mississippi.

Private meteorologist Ryan Maue said: “There will be chaos, potential disaster. We haven’t seen that in a long time.”

American, Delta, Southwest and United airlines are waiving change fees for passengers due to possible flight disruptions.