BISMARCK, N.D. — Some people were choosing to stay indoors as an arctic blast swept across the Northern Plains, but the prospect of temperatures not cracking single digits had a different effect on the roustabouts, roughnecks and thousands of others working outside in western North Dakota’s oil patch.

For them, it was just another challenge to face as they go about the task of pulling nearly a million barrels of oil a day out of the ground.

“This is what I love to do,” said Craig Hovet, during a break from maintenance work on a well near Mandaree. “The joke around here is: This kind of weather keeps out the riffraff.”

Hovet and his crew shrugged off blowing snow and single-digit temperatures on Wednesday, but the real deep freeze was just ahead. Today’s projected high was minus 6 degrees, falling to minus 10 by Saturday, with overnight lows to 24 below as a major winter storm bulldozed from the Rockies eastward.

The National Weather Service forecast a foot or more of snow in some areas of the Upper Midwest, with freezing rain possible for parts of the Great Lakes. To the south, Oklahoma and Arkansas faced a possible ice storm tonight.

Temperatures that had hovered in the single digits across Montana began dropping Wednesday, and the National Weather Service forecast record or near-record lows in several parts of the state overnight. The bitter cold predicted ranged from minus 9 degrees in Missoula to minus 27 in Butte and Shelby.

The extreme cold prompted the Red Cross to release a statement urging people to stay inside or layer up to guard against frostbite if they must go out. The agency also asked residents to check on their neighbors, especially if they require special assistance or live alone.

The cold snap was widespread, blamed on the jet stream’s move southward and expected to linger through much of the week. In Minnesota, the icy blast came with a snow dump approaching 3 feet in the northeast, though much of that was lake-effect snow on the shores of Lake Superior. At least five people died in fatal crashes in Minnesota, plus at least two more in Montana and North Dakota.