CHICAGO (Reuters) - A biting cold blast of arctic air gripped the northern Great Plains and parts of the Midwest on Tuesday, bringing dangerous wind chills and the threat of frostbite, weather officials said.

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The arctic air mass was expected to create wind chills of lower than minus 20 degrees Fahrenheit (minus 29 degrees Celsius) over the coming days in the Northern Plains, a region that includes Minnesota, North Dakota and South Dakota, according to the National Weather Service.

“Ran into a guy at the gas station who thought his journey to Alaska had finally ended....I regrettably informed him that the weather is deceiving and this is only North Dakota,” Facebook user Jason McMillan said in a post on Tuesday.

By the end of the week, the cold air is expected to travel through the Midwest into the mid-Atlantic and Northeast states, the NWS forecast said.

Forecasters have said the cold weather snap could be similar to the life-threatening lows that afflicted some U.S. regions in 2014 due to the polar vortex. The phenomenon is a spinning mass of cold air over the North Pole that delivers icy air into the mid-latitudes during the winter whenever the vortex weakens and splits up.

In Fargo, North Dakota, which was expected to experience some of the coldest temperatures among U.S. cities from the latest chill, it was 7 degrees F (-14 C) on Tuesday afternoon.

With the wind chill, temperatures in the Fargo area on Tuesday could feel like minus 25 to minus 35 degrees F (minus 32 degrees to minus 37 C), according to the NWS.

“Brutal wind chills this morning with values dropping below -30. Cover up and layer up!” Fargo meteorologist Lisa Green said on Twitter.

In those conditions, frostbite - an injury caused by freezing body tissue - can afflict exposed skin within minutes, according to the NWS.

In west central and northwest Minnesota, the NWS warned of a wind chills similar to those in Fargo.

It was around 19 degrees Fahrenheit (minus 7 C) on Tuesday morning in Chicago, but the temperature was expected to drop to around 8 degrees Fahrenheit (minus 13 C) on Thursday.

The Detroit and Pontiac, Michigan, office of the NWS said that the air mass would be the coldest to hit the area since February 2015.

The NWS’s national advisory said heavy snow this week could fall in parts of northern Michigan, Pennsylvania and New York state.