A shaded map showing the temperatures across the US, including wind chill, as of 5 a.m. CST.

  • Temperatures as low as minus 34 degrees Celsius were recorded in Wisconsin in the US on Wednesday morning, part of a wider freezing weather system stretching from New York to North Dakota.
  • Just one weather station in Antarctica managed a temperature lower than that.
  • More than 55 million Americans will experience sub-zero temperatures, and four deaths have already been linked to the deadly weather system.
  • Authorities are warning people that they can get frostbite from spending just five minutes outside.

American cities at the centre of a frigid, deadly weather system are colder than most of Antarctica, as a polar vortex brings record-low temperatures.

La Crosse, Wisconsin, recorded temperatures of minus 34 degrees Celsius (minus 30 in Fahrenheit) at 5.20AM. on Wednesday, according to the US National Weather Service.

AccuWeather data showed that just one weather station in Antarctica recorded a lower temperature at the same time. Most were significantly warmer.

Temperatures have also broken US records: Rockford, Illinois, registered its lowest-ever reading of minus 30 degrees Celsius at 4AM on Wednesday, three degrees colder than the previous record from 1966. 

NWS La Crosse said this morning's temperature may be the "all-time coldest records for the office" since it opened 23 years ago.

Temperatures are expected to fall further.

And it will feel even colder to the 55 million Americans who will experience below-zero temperatures due to wind chill.

This graphic shows how low the temperatures will be around Chicago due to wind chill. Wind chill is colder than regular temperatures, to reflect how wind strips heat away faster than still air.

The actual temperature in DeKalb, Illinois, at midnight on Tuesday was minus 25 degrees Celsius, but the wind chill meant it felt like minus 41 degrees Celsius, according to the NWS.

And it warned: "Temperatures & wind chills will continue to head down, down, down."

At midnight, Minneapolis and its surrounding areas experienced wind chill temperatures as low as minus 51 degrees Celsius.

The NSW predicts that the lowest temperature on Wednesday will be minus 36 degrees Celsius, recorded at Fosston, Minnesota. 

At least four deaths have been liked to the weather as of Tuesday, the Associated Press reported. A man was struck and killed by a snow plow in the Chicago area, a couple's SUV struck another on a snow-covered road in Indiana, and a man in Milwaukee man was found frozen to death in a garage. The NWS and other services have been advising the public on ways to stay safe including wearing extra layers to prevent frostbite.

The service warned on Tuesday that people could get frostbite and hypothermia after spending as little as five minutes outside.

Chicago Public Health advised people in the area: "Chicago, take extra precautions to stay warm & avoid hypothermia & frostbite. Avoid unnecessary trips outside, and if it is necessary to go outside, wear several loose fitting layers of warm clothing. Make sure your cell phone is charged & keep a blanket in your car."

Police stations in Chicago also opened their doors to people who need to escape the cold.

More than 1,700 flights were canceled early Wednesday, largely out of Chicago O'Hare and Chicago Midway international airports, according to flight tracking site FlightAware.

Hundreds of public schools and several large universities from North Dakota to Pennsylvania canceled classes Tuesday or planned to do so Wednesday, the Associated Press reported, while the US Postal Service said it was suspending services in some places because it wouldn't be safe for staff to go outside.

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