The No. 2 U.S. airline said it had canceled around 3,000 flights in the wake of Wednesday's storms that left passengers stranded and frustrated during one of the busiest travel weeks of the year.
Eight of those were to Minnesota, said Patrick Hogan, spokesman for the Metropolitan Airports Commission.
Flight-tracking service FlightAware.com showed 120 canceled flights on Sunday and about 280 delays, as scheduling problems continued after storms Wednesday around the carrier's Atlanta hub and Thursday in the Northeast.
Delta has one of the most enviable track records in the airline industry.
Delta's Chief Operating Officer Gil West released a statement apologizing for the cancellations.
Delta flights into Missoula, Bozeman, and Billings were delayed Sunday as part of an operations nightmare that the airline is only just coming out of after five days. Delta is also offering to waive change fees for those who rebook their plans.
Delta Air Lines is trying to get back to normal after "unprecedented" severe weather grounded thousands of flights.
West said that about 60 percent of Delta's fleet cycles through Atlanta each day, and the impact of a storm like Wednesday's can be significant.
On Twitter, Delta told people who were expecting to fly Friday to check their flight's status before going to the airport. That was the thinking when Delta Air Lines delivered pizza to stranded travelers across the Southeast region. The ground stop was lifted around 1:40 p.m. but not before causing more delays and canceled flights. The airline has apologized.
Some passengers said their bags showed up a day late.