Looming storms shut U.S. government offices

STORY: A powerful thunderstorm system moving across the eastern seaboard caused U.S. government offices in Washington, D.C. to close early on Monday.

The national forecaster said the mid-Atlantic area could see winds exceeding 75 miles per hour.

Strong winds toppled trees in the nation's capital.

While across the east coast, from Alabama to New York, millions of people were told there was a risk of tornadoes late Monday night.

Video on social media showed possible sightings of tornadoes forming in New York on Monday.

Thousands of Americans were also left without power in Maryland and Virginia, due to severe thunderstorms.

Air travel also took a hit. More than 2,600 U.S. flights were canceled, according to a flight tracking site, and another 7,700 were delayed.

The Federal Aviation Administration grounded many departing flights at New York, Washington, Philadelphia, Atlanta and Baltimore airports.