Reuters/Christian Hartmann
The hardest hit airports are Atlantic Hartsfield (the world's busiest), Chicago O'Hare, and Houston Intercontinental.
Over 50% of flights to and from Houston have been cancelled, according to FlightAware.com.
The storm is "anomalous," according to the National Weather Service, which is predicting a "wintry mix" as far south as southern Louisiana and along the Gulf Coast, and "significant icing" across southern Georgia, coastal South Carolina, and southeastern North Carolina.
In an email, FlightAware CEO Daniel Baker explained that Texas is especially unprepared for freezing rain:
The cause of problems at Texas airports (in particular, Houston) is due to forecast freezing rain / sleet. Houston is not equipped for extended or significant frozen precipitation; in addition to airport de-icing limitations, roads (particularly bridges) can become impassable and airport and airline employees are unable to get to the airport.
More than 3,600 U.S. flights have also been delayed, and nearly 400 scheduled for Wednesday have already been cancelled.
You can see how delays and cancellations ripple across the country in FlightAware's Misery Map: