Polar vortex brings coldest air in a generation

It's -35 degrees, in Tower, Minnesota, the finish line for the Arrowhead 135. The windchill is -52.

Despite the absurd cold, some of the runners still finished the race. Some of them crossed the finish line with faces completely encased in ice. Seven runners are still on the course.

Krueger said people from all over the world travel to compete in it. There wasn't even a discussion to postpone or cancel the race because of the polar temperatures.

"They know it's a tough race and honestly people want a tough race," Krueger says. "People want the bragging rights about finishing in the tough years."

Here's a look at some of the participants this morning:

More about the race: Runners start in International Falls, Minnesota, and make a 135-mile slog to the finish at the Fortune Bay Casino in Tower, Minnesota. They can either run, bike, ski or kick sled.

They're equipped with mandatory survival gear and are encouraged to self-rescue —there's only three checkpoints in the race. Krueger says only one racer has quit because of frostbite.  

Today is the final day of the race; participants have until 7:00 p.m. to finish.

The ultra-marathon is grueling, and most racers do not finish. If the final seven runners still on the course finish, that'll mean 13 of 64 runners that started will finish.

None of the skiers or kick sledders finished. Of the bikers, only 39 out of 75 finished.  

To track the final seven participants progress, click here.

In Minnesota, blustery weather could mean wind chills approaching -70. In Ponsford, the wind chill was -66, CNN meteorologist Michael Guy said.

It's so cold, the National Weather Service warned that frostbite could set in in just minutes.

CNN meteorologist Dave Hennen described it as the "coldest air in a generation." Temperatures will plunge to 20-40 degrees below zero between Tuesday and Thursday in the Upper Midwest, Hennen said.

In northern Minnesota, wind chills were forecast to drop to 65-70 degrees below zero, which would rival the coldest wind chill ever recorded in the state (71 below) in 1982.

Sgt. Jesse Grabow, a public information officer in Minnesota, recorded dash-cam video of road conditions on I-94 yesterday.

This footage was shot about 10 miles east of Moorhead, Minnesota:

Snow, rain, heat, gloom and night may not stop United States Postal Service workers from getting out the mail — but this Arctic freeze will.

USPS is suspending service in parts of the Midwest today because of the cold.

Parts of the following states are affected:

As the dipping polar vortex brings insanely cold weather to the Midwest and Northeast, at least 1,944 flights within, into or out of the US have already been canceled this morning, according to FlightAware.

Another 375 flights have been delayed.

Here is FlightAware's look at where the delays are the worst this morning:

It’s brutally cold this morning in many Midwest cities.

It's going to stay cold: Temperatures in both Minneapolis and Chicago will stay at around 15 below zero today.

And it's going to get colder: Chicago will see its coldest readings tonight, and will likely be very close to their coldest reading ever of 27 below zero. It will be even colder in parts of Northern Illinois, where the all time state record could be broken.

Several dozen records are likely to occur today and tonight over a wide area from International Falls, Minnesota, to Washington and New York City, where temperatures will drop to the single digits.

Our live coverage has concluded for the evening, but we'll be back at it Wednesday morning.

Read our latest report: Extreme cold torturing much of the US, Minnesota may see wind chills of minus 70 degrees

The National Weather Service says blizzard warnings are in effect for parts of Michigan's Upper Peninsula until 7 a.m. ET Thursday.

If you're in the area, note that while snow storms are often referred to as blizzards, that's not entirely accurate. Watch this video to understand which weather conditions must occur before a snow storm can technically be called a blizzard.

Lenny Venneman was rear-ended by a semi-truck near Grand Rapids, Michigan.

He was not hurt, and he took this video after the crash as he checked on others involved in the accident.

No one reported any immediate injuries.