Atlanta-based Delta Air Lines has cancelled about 300 flights in the Southeast due to the thunderstorm hitting the area Wednesday.
Delta typically has roughly 1,000 peak-day departures a day from Atlanta.
Flights at Hartsfield-Jackson International Airport were significantly delayed due to the thunderstorms, according to the Federal Aviation Administration.
A ground delay program was in effect early Wednesday afternoon for arriving flights at Hartsfield-Jackson, with flights bound for Atlanta delayed due to the storm. The ground delay program, which ended late Wednesday afternoon, replaced a ground stop.
The average delay for arriving flights early Wednesday afternoon was 2 hours and 46 minutes, according to the FAA. Departure delays were 31 to 45 minutes, the agency reported.
Diversions were also expected, according to Delta.
As flying ramped back up early Wednesday evening, the FAA put in place a ground stop for arriving traffic due to heavy volume.
The FAA, Delta and the airport advised travelers to check their flight status with their airline to find out if it is affected.
Delta said it was "working diligently" to re-book customers who have been affected.
Dallas-based Southwest Airlines, the second-largest carrier in Atlanta behind Delta, also warned that flights in Atlanta may be delayed, diverted or cancelled.
Southwest said Wednesday afternoon it had cancelled 19 of its 125 Atlanta flights. The airline is allowing customers with flights booked for Wednesday to rebook their flights or travel standby within 14 days with no additional charge. Certain terms apply.