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

Elsewhere, the East Coast contended with a thick blanket of snow while people from the Northern Plains to the tip of Maine shivered in bitterly cold temperatures from an Arctic air mass that sent temperatures plunging well below normal Monday with dangerously cold wind chills.

Around 40 million people, primarily across the southern U.S., were under some type of weather hazard, including more than 21 million under a winter storm warning, said Marc Chenard, a meteorologist 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.

Lakesha Reed, manager of Beaucoup Eats catering in New Orleans, had plans to leave Tuesday to cook for a Mardi Gras-style event in the nation’s capital, but flights were canceled amid extreme cold. The 47-year-old New Orleans native said it was in the 30s early Monday afternoon in her port city, where near-freezing temperatures are rare.

“We can barely drive in the rain,” she said. “Last year, we wore shorts for Mardi Gras.”

The online tracker FlightAware reported more than 570 flight cancelations by Monday afternoon within the U.S. or entering or leaving the country, along with more than 5,800 delays.

Winter storm warnings extended from Texas to Florida on Monday, with heavy snow, sleet and freezing rain expected around the region 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, along with extreme cold temperatures.

Snow on the Gulf Coast

Anticipating the storm, governors in Georgia, Louisiana, Mississippi and Alabama, declared states of emergency and many school systems canceled classes Tuesday.

Winter storm warnings were in effect in Texas, Mississippi, Alabama and the Florida panhandle. The storm was expected to impact Texas starting Monday evening, spread eastward through Wednesday morning with heavy snow expected along and to the north of the Interstate 10 corridor with sleet and freezing rain in south Texas and southeast Georgia and northern Florida.

Forecasters warned the sub-freezing 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” once the storm hits, warning any road ice could make travel dangerous. Warming centers were being readied as towns worked to get homeless people off the streets. The weather service warned power outages were possible in areas of significant snow and ice accumulation.

Meanwhile, shoppers packed supermarkets, stocking up.

“Things were really nuts with everyone shopping and trying to get supplies in the past couple days, and most people were looking for the same stuff because they want to make something that will warm your blood, maybe a gumbo,” William Jordan said Monday.

Return of the Arctic blast

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

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

Elsewhere, an area from the Rockies into the Northern Plains will see colder than normal weather over several days, with temperatures forecast to drop to between minus 30 degrees Fahrenheit (minus 34 degrees Celsius) to minus 55 degrees Fahrenheit (minus 48 degrees Celsius) on Monday. Sub-zero wind chills are expected as far south as Oklahoma and the Tennessee Valley.

The weather service issued cold weather advisories across the Great Lakes region as high temperatures in many places were expected only to rise into the single digits or teens Monday and Tuesday. Night-time wind chills could drop temperatures to minus 20 F (minus 29 C) or lower. Chicago’s high Monday only was expected to hit 10 F (minus 12 C), while Monday night’s low was targeted at minus 5 degrees F.

Like earlier this month, this latest cold snap comes from a disruption in the polar vortex, the ring of cold air usually trapped about the North Pole.

In Texas, Jonathan LeBron, 39, plumbing manager at Nick’s Plumbing & Air Conditioning in the Houston area, said the company started getting homeowner calls Monday about worries of frozen pipes.

“There is a little bit of panic,” LeBron said. “I think they’re pretty aware of what’s going on. The last freeze was three or four years ago. They want us to go out there and make sure things are insulated accordingly.”

Houston’s low temperature on Tuesday will be about 18 F (minus 8 C), according to the National Weather Service, or low enough for water to freeze in pipes, expand and then cause the pipes to burst.

Santa Ana winds expected to return to Southern California

In Southern California, where blazes have killed at least 27 people and burned thousands of homes, strong Santa Ana winds were expected to return Monday with gusts between 70 and 90 mph (about 113 to 145 kph), according to Andrew Rorke, senior forecaster with the weather service in Oxnard, California. But he said a small amount of rain in the weekend forecast was a hopeful sign.