Millions of people across the northern Gulf Coast braced Tuesday for a rare winter storm that’s expected to scatter heavy snow, sleet and freezing rain around the Deep South as a blast of Arctic air plunges much of the eastern U.S. into a deep freeze.

The National Weather Service forecast between 3 and 7 inches of snow and sleet for parts of southern Mississippi and southeast Louisiana, including New Orleans, heading into Tuesday.

In Texas, both Houston airports announced flight operations would be suspended starting Tuesday in expectation of hazardous conditions from the severe winter weather taking aim at a huge swath of the South.

Residents from Texas to north Florida were rushing to insulate pipes, check heating systems and stock up on emergency supplies.

Elsewhere, the East Coast endured a thick blanket of snow while people from the Northern Plains to the tip of Maine shivered in bitterly cold temperatures from the frigid arctic air mass that sent temperatures plunging well below normal Monday. Dangerously cold wind chills were expected to persist through Tuesday morning.

Around 40 million people, primarily across the southern U.S. from Texas to Florida, were under some type of weather hazard, including more than 21 million under a winter storm warning, said meteorologist Marc Chenard with the National Weather Service in College Park, Maryland. He added about 170 million people from the Rockies to points eastward were under either an extreme warning or a cold weather advisory.

Winter storm warnings extended from Texas to Florida on Monday into Wednesday. Meanwhile, a state of emergency was declared Monday night across at least a dozen counties in New York as heavy lake-effect snow was expected around Lake Ontario and Lake Erie through Wednesday — with 1 to 2 feet possible — along with extreme cold temperatures.

Forecasters warned the subfreezing morning lows could threaten sensitive vegetation and exposed plumbing in areas unaccustomed to bitter cold.

Across Louisiana, officials urged residents to “stay home” and not “go sightseeing” during the storm, warning any road ice could make travel dangerous. The weather service warned power outages were possible in areas of significant snow and ice accumulation.

Much of the Eastern Seaboard is enduring some of the coldest temperatures this winter.

The cold weather promoted Donald Trump to take the oath as president Monday from inside the Capitol Rotunda, upending months of meticulous planning for a massive outdoor inauguration with crowds sprawling down the National Mall. The last time an inaugural ceremony was held indoors was Ronald Reagan’s in 1985.