An astonishing, dangerous cold snap is about to descend on the U.S.

For days, it’s appeared on computer model maps in the form of deep blue and purple shades. Now it’s about to get real and up close and personal. Some of the coldest air in years, if not decades, is poised to pour into the U.S., with mind-boggling low temperatures.

Basically a large whirlpool in the atmosphere originating at the north pole – in geek speak known as the polar vortex – is diving into the Lower 48.

The polar vortex (as simulated by the circulation at 500 mb in the GFS model) dives into the Great Lakes Monday night (WeatherBell.com)

The polar vortex (as simulated by the circulation at 500 mb in the GFS model) dives into the Great Lakes Monday night (WeatherBell.com)

Climate Central’s Andrew Freedman describes it this way:

The polar vortex is an area of cold low pressure that typically circulates around the Arctic during the winter, spreading tentacles of cold southward into Europe, Asia, and North America at times. Except this time, it’s not a small section of the vortex, but what one forecaster, Ryan Maue of WeatherBELL Analytics, called “more like the whole enchilada” [that's visiting the eastern U.S.]

How cold is the air that’s coming?

Let’s start in Montana on Sunday night, when wind chills may go as low as 62 below, according to the National Weather Service in Glasgow.

Forecast hazard overview for northeast Montana (National Weather Service)

Forecast hazard overview for northeast Montana (National Weather Service)

It’s not out of the question parts of northern Minnesota experience wind chills down to 70 below.

In Minneapolis, the National Weather Service is forecasting wind chills Monday morning from 45 to 60 below zero. It calls the incoming cold air outbreak “historic”, predicting it will be the most severe since 1996. “Highs of 10 to 20 below and lows of 15 to 30 below are expected,” it warns.

Forecast hazard overview for area around Minneapolis (National Weather Service)

Forecast hazard overview for area around Minneapolis (National Weather Service)

So extreme is the expected cold that Minnesota governor Mark Dayton has closed all public schools Monday, reports the NY Times.

The playoff matchup between the Packers and San Francisco 49ers at Green Bay’s Lambeau field Sunday evening may match or even surpass the coldest NFL game on record, the Ice Bowl (December 31, 1967) which was played at 13 below in Green Bay.

“Low temperatures may fall to 30 below over north-central portions of Wisconsin … Monday and Tuesday morning,” writes the National Weather Service office in Green Bay. “If you plan on being outside, be sure to dress warm using layered clothing if possible, as frost bite can occur in as little as 10 minutes in these conditions.”

The punishing cold snap will also blast Chicago.

The Chicago Weather Center predicts starting Sunday night “a non-stop 60 hour stretch of temperatures which fail to break above 0-degrees” – the longest such period of the past 18 years.

The core of the cold reaches the Ohio Valley and East Coast Monday night into Tuesday, when temperatures drop 20 to 40+ degrees below normal.

Temperature difference from normal forecast by the European model Tuesday morning (WeatherBell.com)

Temperature difference from normal forecast by the European model Tuesday morning (WeatherBell.com)

Especially if snow cover lingers (or is replenished by the arctic front Monday), it’s possible all of the I-95 cities from D.C. to New York City drop below zero for the first time in nearly 20 years. Writes Paul Dorian at SIWeather.com:

Not since January of 1994, the winter still remembered around here as the “ice storm” winter, have we seen below zero readings in New York City, Philadelphia and Washington, DC – all at the same time. On January 19th, 1994, Central Park, NY reached -2 degrees, Philly Airport bottomed out at -5 degrees, and Reagan National Airport in DC reached -4 degrees.

The European model, shown below, shows lows in flirting with zero throughout this zone (the GFS model, now shown, is slightly colder).

Low temperature forecast from the European model Tuesday morning (WeatherBell.com)

Low temperature forecast from the European model Tuesday morning (WeatherBell.com)

The cold air will slowly begin retreating Wednesday.

Also on Capital Weather Gang

Snowstorm crushes New England with up to two feet of snow