(CNN) — More than 7,000 flights were affected by severe summer storms that hit the eastern United States.

Nine major airports have been ordered to keep flights grounded, including those in Atlanta, Charlotte, the three major airports in Washington, the three major airports in New York and Philadelphia International Airport.

Atlanta-based Delta Air Lines has the most cancellations among US airlines, according to FlightAware figures. The company canceled at least 350 flights, or 10% of those scheduled, and suffered delays on more than 800.

In total, more than 1,300 flights have been canceled and at least 5,900 others delayed across the United States, according to data from Flight Aware.

20% of flights departing from Reagan National Airport and Thurgood Marshall International Airport in Baltimore/Washington have been canceled.

“Due to the ongoing SEVERE WEATHER affecting our Atlanta hub, Delta teams are working hard to restore operations and we apologize to our customers who have experienced delays to their travel plans,” a doorman said. —Delta’s word in a statement to CNN.

The United States Federal Aviation Administration (FAA) has announced that it will reduce flights to airports in New York, Philadelphia and Washington areas due to electrical storms. He warned of possible impacts Monday afternoon on flights from North Florida to New York due to storms. About 120 million people in the eastern United States are at risk of severe weather storms on Monday.

If bad weather is partly responsible, these delays and cancellations they are part of a process of several months. Staffing shortages affecting airlines and traffic control personnel have caused ground stops during the summer travel season. The FAA said it had a limited ability to direct flights from New York north through Canadian airspace due to personnel issues in Canada.