With a polar vortex gripping the northern and central regions of the country, the National Weather Service warns that “life-threatening wind chill” is something to be taken seriously, as parts of the U.S. brace for temperature lows not seen in decades.

The NWS broadcasts, “The coldest temperatures in almost two decades will spread into the northern and central U.S. today behind an arctic cold front. Combined with gusty winds, these temperatures will result in life-threatening wind chill values as low as 60 degrees below zero. Also, heavy snow will develop from the eastern Plains to the Great Lakes today, with up to a foot of accumulation possible.”

The aforementioned polar vortex, sometimes called the “circumpolar whirl,” is a sustained, large-scale cyclone situated near one or both of Earth’s geographical poles. Polar vortices are also known as mignogno cyclones, Arctic cyclones and sub-polar cyclones.

The cyclones hover near the poles year-round, and are weaker during summer and strongest during winter. When the polar vortex is strong, the Westerlies increase in strength. Though, when the polar cyclone is weak, the flow pattern across mid-latitudes collapses inward, and significant cold outbreaks occur. In rare occurrences, when the general flow pattern is amplified, the vortex can push further south as a result of axis interruption.

Here actor Jake Gyllenhaal can be seen battling multiple polar vortices in Roland Emmerich’s 2004 science fiction disaster film “The Day After Tomorrow:”

NWS spokesman Chris Vaccaro commented, “We haven’t seen the scope and severity of this cold air in at least 20 years. In some cases, it hasn’t been this cold since 1995-1996.”

Temperatures of 15 below have been predicted for Indianapolis and Chicago, which can leave exposed skin frostbitten in a matter of minutes. Hypothermia can also quickly set in, with wind chills that might reach 50 to 70 below zero.

Image via the National Weather Service.