SIOUX FALLS, S.D. (AP) — It has been decades since parts of the Midwest experienced a deep freeze like the one expected to arrive this weekend. Potential record-low temperatures starting Sunday and expanding into next week are increasing fears of frostbite and hypothermia even in a region where residents are accustomed to bundling up.

This “polar vortex,” as one meteorologist calls it, is caused by a counterclockwise-rotating pool of cold, dense air. The frigid air, piled up at the North Pole, will be pushed down to the U.S., funneling it as far south as the Gulf Coast.

Temperatures are projected to dip to 25 below in Fargo, N.D., and minus 31 in International Falls, Minn. The San Francisco-Green Bay playoff game Sunday at Lambeau Field could be one of the coldest NFL games ever played.