BUFFALO, N.Y. — Brutally cold temperatures and dangerous wind chills stayed put across much of the U.S. on Monday, promising the coldest temperatures ever for Iowa’s presidential nominating contest, holding up travelers and testing the mettle of NFL fans in Buffalo for a playoff game that was delayed a day by wind-whipped snow.

About 150 million Americans were under a windchill warning or advisory for dangerous cold and wind, said Zack Taylor, a meteorologist with the National Weather Service in College Park, Maryland, as an Arctic air mass spilled south and eastward across the U.S.

Sunday morning saw temperatures as low as minus 20 degrees Fahrenheit to minus 40 F in northern and northeast Montana. Saco, Montana, dropped to minus 51 F. Subzero lows reached as far south as Kansas, Missouri, Illinois and parts of Indiana, Taylor said.

About 114,000 U.S. homes and businesses were without power late Monday, the bulk of them in Oregon after widespread outages that started Saturday. Portland General Electric warned that strong winds forecast for Monday and threat of an ice storm Tuesday could delay restoration efforts.

The storm was blamed for at least four weekend deaths around Portland, including two people who died of suspected hypothermia. Another man was killed after a tree fell on his house and a woman died in a fire that spread from an open-flame stove after a tree fell onto an RV.

Three deaths of homeless people were under investigation in the Milwaukee area. They likely died from hypothermia, officials said. A 64-year-old man was found dead under a bridge Friday’ a 69-year-man was pronounced dead after being found in a vehicle on Saturday, and on Monday a 40-year-old man was found dead near railroad tracks, the Milwaukee County Medical Examiner’s Office said.

Classes were canceled Tuesday for students in major cities including Chicago — the nation’s fourth-largest public school district — Portland, Denver, Dallas and Fort Worth.

In Utah, where almost four feet of snow fell in the mountains over a 24-hour period, a snowmobiler was struck and killed Sunday night by a semitrailer about 70 miles southeast of Salt Lake City, according to the Utah Highway Patrol. The victim was attempting to cross U.S. Highway 40.

In Wyoming, a backcountry skier was killed after triggering a 50-feet wide avalanche. The victim was swept into a gully and through brush and trees, then remained buried for about 15 minutes before being found by a companion in the mountains south of Alpine, Wyoming, on Sunday afternoon, according to the Bridger-Teton Avalanche Center.

It marked the third U.S. avalanche fatality in recent days, following a Wednesday accident at a California ski area that killed one person and injured three others, and another that killed a person on Thursday in the Idaho backcountry near the Montana border.

Swirling snow and avalanche dangers prompted numerous road closures across the Rocky Mountains. East of the resort community of Vail, Colorado, officials closed a 20-mile stretch of Interstate 70, the primary east-west highway through the state.

Crews on Monday continued clearing snow after a weekend avalanche briefly trapped the occupants of 10 cars and shut down the road over Berthoud Pass in central Colorado. Kaitlyn Punzalan was in a car with her husband and some friends heading home to Denver when they were caught in the slide.

“My friend was driving my car and all of a sudden he goes — ‘Ah, avalanche!’ And we just look up and see all of this snow coming down towards us,” Punzalan told KUSA-TV. She said it took them about an hour to dig out, with help from others who were on the road. No injuries were reported.

Presidential campaigns were expecting the cold and dangerous travel conditions to hamper turnout for the Iowa caucuses, the opening contest in the monthslong Republican presidential primary. Voting was set to begin Monday night.

Air travelers across the country experienced delays and cancellations. The flight tracking service FlightAware reported about 2,900 cancellations Monday within, into or out of the United States.

Freeze warnings were issued by the National Weather Service across the Deep South. Mississippi forecasters warned of a “long duration freeze” that would last in some locations until Thursday.

Highs of 15 or 20 degrees F were expected across Oklahoma, Arkansas, northern Texas and western Tennessee. Louisiana and Alabama also had freeze warnings.

The winter storm was affecting travel across the central Appalachian region, with areas of Tennessee seeing as much as 8 inches of snow. The snow was expected to continue accumulating through early Tuesday with bitter cold wind chills.

With the potential for record low temperatures in Texas, the state’s electrical grid operator asked consumers to conserve energy. About 11,000 Texas customers were without power Monday, according to poweroutage.us.

Light snow was expected through the Mid-Atlantic and the Northeast through Monday and Tuesday, Taylor said, including 2 to 3 inches of snow forecast for Washington, D.C. — what would be the most snowfall in a day in the nation’s capital in at least two years.

4 deaths in Oregon

About 114,000 U.S. homes and businesses were without power Monday, the bulk of them in Oregon after widespread outages that started Saturday. Portland General Electric warned that strong winds forecast for Monday and threat of an ice storm Tuesday could delay restoration efforts.

The storm was blamed for at least four weekend deaths around Portland, including two people who died of suspected hypothermia. Another man was killed after a tree fell on his house and a woman died in a fire that spread from an open-flame stove after a tree fell onto an RV.