American Airlines canceled hundreds of flights over the Halloween weekend, blaming weather woes and staffing issues.

According to data from aviation tracking website Flight Aware, the airline canceled 527 total flights on Sunday, accounting for nearly one-third of all cancellations in the country. Another 31 flights, or 1%, were canceled.

On Saturday, American canceled 543 flights. According to data, another 407 flights, or 15% of its flights, were delayed.

In a note to employees on Saturday, American COO David Seymour blamed the delays on poor weather conditions around Dallas-Fort Worth International Airport, the airline’s base of operations.

Following massive staff reductions during the COVID-19 pandemic, American announced that 1,800 flight attendants will return from leave on November 1 to prepare for the holiday travel season, with more expected to return on December 1.