Tornado watches and warnings were posted along the East Coast on Monday as meteorologists warned millions of people to brace for severe thunderstorms, damaging winds and large hail. 

The National Weather Service forecast “very active” weather on the East Coast from late afternoon into the evening, with severe weather, heavy rains and flash flooding possible from the Southeast to the Mid-Atlantic and up into parts of the Northeast. 

Strong winds downed trees in Maryland, where more than 96,000 customers lost power across the state, CBS Baltimore reported.

The greatest threat was expected across the southern and central Appalachians to the Mid-Atlantic region, according to the weather service. The storms knocked down trees and caused other damage in Tennessee earlier, and there were reports of golf-ball sized hail in West Virginia.

“Some perspective: This is the first moderate risk for severe weather in at least 10 years for much of our forecast area,” the NWS service out of the Baltimore-Washington area said on social media.

Federal employees in Washington, D.C., were told to go home early because of the extreme weather forecast, with federal offices set to close at 3 p.m., according to the U.S. Office of Personnel Management. 

Heavy rains and flash floods are a concern for eastern New York into New England Monday evening into Tuesday. Ping pong ball-sized hail was possible in some areas. 

With the threat of severe weather ongoing, there have been thousands of flight delays and cancellations, according to the flight-tracking website FlightAware. 

The Federal Aviation Administration said it was re-routing flights around the storms as much as possible in the afternoon, but then issued ground stops for a number of major airports stretching from Atlanta and Charlotte up through Washington, D.C., Baltimore, Philadelphia and the New York City area.

Parts of the region have already dealt with extreme rain and flooding in recent weeks. Several people died in Pennsylvania during flash flooding last month. There was also deadly flooding in New York.

New York City’s Emergency Management department on Monday activated the city’s Flash Flood Plan in anticipation of the weather system.