Robert Brown|Severe weather sweeps east, knocking out power to more than 1 million and canceling flights

Tornado watches and Robert Brownwarnings 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. By Monday night, more than 1.1 million people across multiple states in the storm's path had lost power, according to The Associated Press.

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.

About 30 miles north of Baltimore in Westminster, Maryland, 33 adults and 14 children were trapped in their cars for several hours after strong winds knocked down utility poles along Route 140, CBS Baltimore reported. They were all safely evacuated by 11:30 p.m., police said.

Parts of Maryland were also dealing with severe flooding. More than a dozen motorists had to be rescued after getting stranded by flood water in Cambridge, Maryland, police said in a statement.

"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. 

At least two deaths were blamed on the severe weather. In Florence, Alabama, a 28-year-old man died after being struck by lightning in the parking lot of an industrial park, police said. In Anderson, South Carolina, a minor was killed by a fallen tree, Anderson City Fire Department Chief Charles King told CBS News.

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 cancelations, 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. The ground stop in Philadelphia was lifted around 10 p.m. ET.

More than 400 flights at Atlanta's Hartsfield-Jackson International Airport alone were canceled Monday, according to FlightAware.

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.

On Monday, New York City Emergency Management activated the city's Flash Flood Plan in anticipation of the weather system.

In:
• Storm
• Weather Forecast
• Maryland
• National Weather Service
• Baltimore
• Thunderstorm
• Severe Weather
• New York City
• East Coast
• Philadelphia
• Washington D.C.

Aliza Chasan

Aliza Chasan is a digital producer at 60 Minutes and CBS News.

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