Record-breaking cold has hit the Midwest, and more than 1,500 flights into and out of Chicago's O'Hare International Airport today have been cancelled.

The National Weather Service is warning of "bitterly cold" conditions, with highs from -9 to -13 degrees, and wind gusts up to 40 mph.

Planes are no strangers to strong wind and freezing temperatures — it's about -60 degrees at 39,000 feet, airline pilot, blogger, and author of Cockpit Confidential Patrick Smith told Business Insider, but low temperatures cause other problems.

"Cold-weather delays and cancelations are more commonly due to ancillary effects on personnel, vehicles and ground equipment, etc," he said.

There's also the issue of ice and snow on the runways, which make takeoffs and landings more dangerous.

According to FlightAware.com, over 60% of flights scheduled to take off from or land at O'Hare today have been cancelled. More than 300 flights scheduled for Tuesday have already been cancelled as well.

Here's how the airport looked Monday morning:

According to Twitter user Sarah Mackey, it's so cold in the airport people can see their breath:

Yes, you can see your breath inside O'Hare airport... That's a new kind of cold! #polarvortex — Sarah Mackey (@sarahwmackey) January 6, 2014

Not surprisingly, that's created some major lines at the airport. Here's a photo from CNBC's Phil LeBeau:

Pic of the day: Thousands delayed, cancelled. waiting in customer service line at O'Hare. pic.twitter.com/f8X1UGEdDc — Phil LeBeau (@Lebeaucarnews) January 6, 2014

New York's JFK Airport was shut down Sunday morning after a Delta plane skinned off a runway, into the snow. No injuries were reported.