MISSION, Kan. (AP) — Temperatures plunged far and fast Thursday as a winter storm began forming ahead of Christmas weekend, promising heavy snow, ice, flooding and powerful winds across a broad swath of the country and complicating holiday travel.

The National Weather Service reported that temperatures across the central High Plains plummeted 50 degrees Fahrenheit in just a few hours. In much of the country, the Christmas weekend could be the coldest in decades.

The storm was so large and encompassing that around 190 million people were under some type of winter weather advisory, the weather service had said Wednesday.

Authorities across the country are worried about the potential for power outages and warned people to take precautions to protect older and homeless people and livestock — and, if possible, to postpone travel.

“If you don’t have to be out driving, especially on Friday, we ask that you don’t be out there,” said Ron Brundidge, Detroit’s public works director.

Jean-Paul Blancq got to Boston’s Logan Airport a day early for his Thursday flight home to New Orleans. Blancq had to take a bus to Logan from his seasonal job in New Hampshire and was unsure of the storm’s path.

“I hope that my flight doesn’t get canceled because I don’t know what I’ll do,” Blancq said.

Bus and train travelers also braced for cancellations and delays.

In Montana, several ski areas announced closures Wednesday and Thursday because of the extremely cold air and sustained winds. Others scaled back offerings. Schools were also closed due to the cold.