A portion of the polar vortex, the pool of subfreezing air that normally swirls over the Arctic Circle, dives into the Midwest this week, pushing temperatures off a cliff. The most intense cold will last from Tuesday night through Thursday across a broad region from North Dakota south into Missouri and as far east as Upstate New York. Temperatures are forecast to run as much as 50 degrees below average for late January.

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Some forecasts Monday were calling for temperatures to drop to minus-29 in Chicago, two degrees below its lowest temperature on record, set on Jan. 20, 1985. Even if the record is not broken, the National Weather Service in Chicago is calling this week’s forecast “life-threatening extreme cold” that “can lead to rapid onset of frostbite and hypothermia.”

The wind chill will plunge to minus-30 to minus-40 as far south as Illinois and northern Indiana. The wind chill temperature, which is a measure of what the air fees like when wind is taken into account, will fall as low as minus-65 in the Upper Midwest.

A recent report from the Centers for Disease Control and Prevention found that cold weather is responsible for the majority of weather-related fatalities. The wind chill temperature is more than a catchy forecast term. The wind blows away the insulating layer of warm air around us generated naturally by our bodies. Wind chill attempts to quantify the effect in terms of how it feels on our skin, which is why you’ll sometimes hear it called the “feels like” temperature. A wind chill of minus-20 degrees can cause frostbite in as little as 30 minutes.

The cold air is riding behind an Arctic front that brought several inches of snow to the same region over the weekend. The pure white ground will enhance the chill, as sunlight reflects off the snow and back to space instead of being absorbed into the ground where it could warm things up.

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In Des Moines, where the wind chill may dip to minus-40 on Wednesday, the National Weather Service advised home and business owners to make sure they are ready for the impending cold snap. “Make sure your heating system, pipes, etc. are as well-prepared as possible,” it advised. “It may be wise to stock up on groceries between now and Monday evening so outdoor time is minimized.”

There’s no arguing the Minneapolis-St. Paul metro area is winter-hardy and has endured many polar vortex visitations before. The Twin Cities Weather Service office, where the wind chill is expected to plunge to minus-50, pulled out the real talk on Sunday. "There’s no sugarcoating it, the weather will get extremely cold,” it tweeted. On top of temperatures that will make you want to never leave the house, wind gusts up to 35 mph over fresh snow could cause periodic whiteout conditions on the roads.

The National Weather Service in Chicago says the temperatures in its forecasts are the coldest in 25 years for the region. Dozens of cities have forecasts at least within one degree of record cold temperatures, including Chicago, Des Moines, Cleveland, Detroit and Minneapolis.

Potential records

The maps below show forecast high temperatures Wednesday afternoon and low temperatures early Thursday morning. The temperatures circled are within one degree of the current record at that location.

Coldest wind chill expected

Grand Forks, N.D. — Minus-57

Minneapolis — Minus-50

Milwaukee — Minus-45

Chicago — Minus-45

St. Louis — Minus-20

Detroit — Minus-35

Cleveland — Minus-32

Pittsburgh — Minus-20