As airlines prepare for what is predicted to be the busiest Thanksgiving ever and even more Americans get set to to hit the road for the long holiday weekend, stormy weather could upend plans for tens of millions.

More than 10 million people have already passed through TSA checkpoints since Thursday, pacing far ahead of even 2019’s pre-pandemic numbers. Nearly 50,000 flights are expected on Wednesday alone. To handle the load, the Federal Aviation Administration is opening up extra airspace usually reserved for the military along the East Coast.

For those in the South hoping to get an early start to their journey, dangerous storms, including the possibility of tornadoes, are sweeping through Louisiana, Mississippi and Alabama on Monday night and Tuesday. The system could also bring golf ball-sized hail, according to The Weather Channel meteorologist Chris Warren.

As the storms move through the Ohio Valley, they’ll bring considerable rain from Detroit to Nashville and along the Gulf Coast.

That same system will then make its way farther east, impacting portions of the Mid-Atlantic and the Northeast in the days just before Thanksgiving. Gusty wind and heavy rain are in the forecast, with the worst of it coming late Tuesday and early Wednesday morning.