MADISON, Wis. (AP) — The Upper Midwest remains locked in the deep freeze, with bitter temperatures stretching into a fourth day across several states.

The cold snap arrived Saturday night as waves of Arctic air swept south from Canada, pushing temperatures to dangerous lows and leaving a section of the country well-versed in 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.

Among the coldest temperatures recorded Tuesday was 35 below at Crane Lake, Minn., a National Weather Service forecaster said early today.

The coldest location in the lower 48 states Monday was Embarrass, Minn., at 36 below. On Sunday it was Babbitt, Minn., at 29 below, according to the National Weather Service.

Forecasters said late Tuesday that overnight temperatures wouldn’t get that low, but warned it was still frigid: Embarrass, Minn., was up to 15 below by late Tuesday night.

Nighttime temperatures around 10 degrees made it harder for Chicago firefighters to battle a warehouse blaze described by officials as one of the largest in recent years. The Chicago Sun- Times reported late Tuesday that more than 170 firefighters responded to the fivealarm blaze at an abandoned warehouse on the city’s South Side that took nearly three hours to get under control.

The Northeast was also feeling the chill from Ohio to Maine.

In Connecticut, overnight temperatures were expected to range from 0 to 10 degrees over the next several days, and the wind chill could make it feel as cold as minus 15 degrees in some parts of the state. In Millinocket, Maine, residents awoke to temperatures of minus 9 degrees.

The bitter conditions were expected to persist into the weekend in the Midwest through the eastern half of the U.S., said Shawn DeVinny, a National Weather Service meteorologist in suburban Minneapolis.