The Federal Aviation Administration ordered a ground landing at DFW International Airport on the morning of Christmas Eve due to weather and thunderstorms, which caused delays for several passengers traveling over the holiday.

Here’s what you should know about flight delays at DFW Airport during the busiest travel season of the year.

Why are flights stopped?

Due to weather conditions, a ground stop was ordered at the airport after 7:30 a.m., leaving all aircraft on the ground.

According to the National Weather Service, thunderstorms, some with the possibility of gusty winds and hail, are expected to sweep across the D-FW area throughout the day. The showers could potentially bring between half an inch and three-quarters of an inch of rain.

According to the FAA, the ground stop could be lifted later Tuesday. However, there is a medium probability that it could be extended, the statement says.

This morning’s weather-related layover could exacerbate delays for American Airlines passengers, whose flights were previously grounded due to an issue other than the storms.

System problems at American Airlines

Shortly before 6 a.m. Tuesday morning, the FAA ordered that all American Airlines flights in the United States would be grounded at the airline’s request. The Fort Worth-based airline had reported a technical issue that affected its entire system and caused millions of passengers to travel on vacation.

The issue was a “provider technology issue” that “impaired flights in the short term,” the airline said in a statement before 8 a.m. The issue affected systems required to release flights.

“We sincerely apologize to our customers for the inconvenience this morning. It’s all hands on deck as our team works diligently to get customers where they need to go as quickly as possible,” the airline’s statement said.

A post on the FAA’s website confirmed the airline’s call for a “nationwide grounding” of all aircraft operated by American Airlines and its subsidiaries. According to the airline, the ground stop lasted about an hour.

American Airlines flights have now been cleared to take off by regulators.

Several passengers who spoke with The Dallas Morning News On Tuesday it was said that there had not yet been any delays. However, some reported delays of around 60 to 90 minutes, but said they were unsure whether this was due to network disruption or weather.

Delays in wet conditions

DFW Airport has experienced repeated flight delays in the past due to severe weather conditions and thunderstorms.

Recent delays include a situation in May when thousands of travelers from North Texas were canceled or delayed due to bad weather in the last week of May. Over Memorial Day weekend, many travelers got stuck at the airport or had to return home because a flight didn’t take off.

According to a news release, DFW International Airport expected its “busiest winter holiday season on record,” with an estimated 4.7 million passengers traveling through the airport from Dec. 20 to Jan. 7.

The Transportation Security Administration expects 40 million passengers to be screened over the holidays and through Jan. 2.