Another day of frigid wind chills and brutal cold across much of the U.S.

Brutally cold temperatures and dangerous wind chills stayed put across much of the U.S. 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 wind chill 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 (minus 6.7 degree Celsius) to minus 40 F in northern and northeast Montana. Saco, Montana, dropped to minus 51 F (minus 26 C). Subzero lows reached as far south as Kansas, Missouri, Illinois and parts of Indiana, Taylor said.