A second round of snow began to fall in Minnesota on Wednesday as forecasters warned of a major winter storm that could make travel dangerous for wide swaths of the nation.

The «twin cities» of Minneapolis and St. Paul are forecast to get up to an additional 12 inches of snow from 6 p.m. Wednesday to 6 p.m. Thursday, the National Weather Service said, on top of the 5 inches that have already fallen.

“Minnesotans are no strangers to extreme weather, but this storm could break records,” Governor Tim Walz said in a declaration Wednesday.

More than 55 million people, from the Northern Plains to Boston and Maine, and along the west coast of the US, were under winter weather warnings or advisories Wednesday night, according to the weather service.

Blizzard warnings were issued for another 2 million, and ice storm warnings affected 8 million.

In the Los Angeles area, blizzard warnings have been issued for the mountains. The only other time that seems to have happened was in 1989, the weather service in Oxnard said.

A series of low-pressure waves traversing an Arctic cold front was causing heavy snowfall and blizzards across the Plains and Midwest, the weather service said, with major travel disruptions likely.

“Luckily, our plane arrived, but it seemed like 90 percent of the flights were cancelled,” said Ann Viksnins, who flew into a surprisingly empty Minneapolis airport on Wednesday. «It’s really creepy here at the airport.»

The Minneapolis-Saint Paul International Airport had more than 400 cancellations Wednesday, the airport said.

Lt. Andrew Siebenborn of Sioux Falls, South Dakota, police joked to reporters that he made it «probably about 11 feet» to the end of his driveway before his patrol car got stuck.

«We’re really not even in the bad part of the coming storm, and we expect it to get a lot worse,» Siebenborn said Wednesday. He encouraged people to stay home and wait.

About 8 ½ inches of snow had fallen at the city’s airport as of 10 p.m. Wednesday, and the weather service expected the last round of snow to fall 1 inch an hour after midnight.

The Arizona Department of Transportation closed parts of at least eight interstate or state routes Wednesday due to the winter storm. About 3 to 6 inches of snow fell in the Flagstaff area, with wind gusts up to 50 mph, the weather service said.

The risk of heavy snow in the western US will mainly be in California on Thursday and Friday due to a new storm, according to the weather service.

The Southern California blizzard warning is for mountains in Los Angeles and Ventura counties, the weather service said, from 4 a.m. Friday to 4 p.m. Saturday. The mountains could see 5 feet of snow, she said.

Minneapolis and St. Paul were under a winter storm warning through noon Thursday, with forecasters warning that the most difficult travel conditions were expected through Thursday morning.

Green Bay, Wisconsin, was in winter storm warning until 6 p.m. Thursday, and the advisory for Bangor, Maine, expired at 10 p.m.