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Data: National Weather Service; Map: Harry Stevens/Axios

An extreme winter weather event is unfolding across the Midwest on Wednesday, and by the end of the day, numerous daily and all-time temperature records will be shattered.

The big picture: An air mass that originated in the High Arctic is currently swinging across the Great Lakes, sending some air temperatures plummeting below minus 30°F. Combined with winds of 40 miles per hour at times, wind chills are reaching dangerous levels below minus 50°F, and in some cases below minus 60°F in parts of Minnesota, Wisconsin, Iowa, Illinois, and Michigan.

Details: Typically, when cold outbreaks hit the Midwest, meteorologists take on a reassuring demeanor, letting their audience know that this is the type of cold they've experienced before.

That's not the case this time. Here's what the NWS forecast office in Des Moines stated on Tuesday:

  • "THIS HAS THE POTENTIAL TO BE LIFE-THREATENING COLD AIR!!! This is the coldest air many of us will have ever experienced. This is not a case of 'meh, it's Iowa during winter and this cold happens.' These are record-breaking cold air temperatures, with wind chill values not seen in the 21st century in Iowa."

Depending on the location, Wednesday and Thursday are likely to be the coldest days in 20-plus years.

In Chicago, the all-time record for the coldest daytime high temperature is likely to be tied or broken, with temperatures only climbing to minus 11°F. Similar records are in jeopardy in South Bend, Indiana, Kalamazoo, Michigan, and Rockford, Illinois.

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Data: ThreadEx, WeatherBell; Chart: Harry Stevens/Axios

Residents of Minneapolis and Des Moines are being warned to limit their exposure to the cold to mere minutes, given the possibility of frostbite.

The climate context: This extreme weather event comes courtesy of a lobe of the polar vortex, which has swirled its way southward, out of the high Arctic, to strafe the Midwest and Northeast with a taste of the winter weather normally felt in far northern Canada.

And we're going to be seeing more of these. Even though we think of climate change as rising global temperatures, recent studies show that it could cause more frequent southward polar vortex incursions too — because as it melts Arctic sea ice, it alters the exchange of heat and moisture between the ocean and atmosphere in the Far North.

Scientists are still debating the physical drivers behind this process, and it's an area of active research.

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