Southwest Airlines canceled 500 flights, 15% of its schedule, Tuesday as it struggled with connectivity issues, a day after technical problem with a weather data supplier delayed hundreds of flights.

The Federal Aviation Administration briefly issued a nationwide ground stop for Southwest, which prevents its flights from taking off to avoid overwhelming destinations.

More than 1690 Southwest flights were delayed on Tuesday, close to half of the carrier’s schedule, according to flight tracking site FlightAware. The airline said operations were returning to normal by Tuesday afternoon.