Atlanta-based Delta Air Lines said Monday it has canceled about 800 flights throughout its system due to bad weather, with most of the cancellations at its hubs at New York’s LaGuardia and John F. Kennedy International airports.

Delta also had a system glitch Monday, with the airline telling customers on Twitter that its system was down, causing slow response times on its website, mobile apps and at airports, and that its IT team was working to fix the problem. In a statement apologizing for the inconvenience, Delta said some of its flights have departed late as a result. The airline said customers have been able to check-in using airport self-service kiosks. Just after 5:30 p.m. Delta said its airport systems and mobile apps were returning to normal.

Delta last Friday offered to waive certain change fees for storm-affected customers who wanted to change their plans, allowing some to travel ahead of the storm.

Southwest Airlines, the second-largest carrier at Hartsfield-Jackson, said it canceled “a significant number of morning flights” in the Northeast on Monday morning, with 300 cancellations on Monday. Southwest said it also reduced its flight schedule at Chicago Midway.

Passengers scheduled to travel to or from areas affected by storms can check their flight status on airlines’ websites.