MADISON, Wis. (AP) – Homeless people scrambled to find shelter, schools closed down and plumbers wrestled with frozen pipes Tuesday as the Upper Midwest endured a third straight day of bitter cold temperatures.

Waves of frigid Arctic air began sweeping south from Canada on Saturday night, locking the Midwest in a deep freeze that has left a section of the country well-acquainted with winter’s pains reeling. Authorities suspect exposure has played a role in at least four deaths so far.

“I am wearing a Snuggie under a top and another jacket over that,” said Faye Whitbeck, president of the chamber of commerce in International Falls, Minn., a town near the Canadian border where the temperature was minus 30 on Tuesday morning. The so-called “Nation’s Icebox” reached a balmy 3 below for a high. “I pulled out a coat that went right to my ankles this morning and I wore two scarves.”