Southwest Airlines on Sunday canceled about 27% of its scheduled flights, accounting for more than 1,000 flights. The airline blamed disruptions on air traffic control issues and bad weather.

No other carrier experienced the same problems.

“We experienced weather challenges in our Florida airports at the beginning of the weekend, challenges that were compounded by unexpected air traffic control issues in the same region, triggering delays and prompting significant cancellations,” Southwest said in a statement on Sunday.

“We’ve continued diligent work throughout the weekend to reset our operation with a focus on getting aircraft and crews repositioned to take care of our customers.”

Cities that have been affected the most by cancelations by Southwest on Sunday were Denver, Baltimore, Dallas Love Field, and Chicago Midway.

“We know the frustration flight cancellations are creating for our customers and employees and we apologize, and we again thank everyone for patience as we work first to be safe, and second to be as quick as possible in solving disrupted plans.”

The FAA announced that there were weather and staffing issues at Jacksonville Air Route Traffic Control Center.

“Flight delays and cancellations occurred for a few hours Friday afternoon due to widespread severe weather, military training and limited staffing in one area of the Jacksonville Air Route Traffic Control Center,” the agency said. “Some airlines continue to experience scheduling challenges due to aircraft and crews being out of place.”