Officials gave the all-clear Wednesday afternoon at the National Mall in Washington, D.C., after severe storms rolled through the area, prompting tornado warnings and a temporary evacuation of the open spaces surrounding the U.S. Capitol and Washington Monument.

For about two hours, U.S. Park Police and U.S. Capitol Police evacuated thousands of people away from popular viewing areas for the Independence Day fireworks events scheduled for later in the evening. The National Weather Service had placed all of neighboring Maryland under a tornado watch until 10 p.m. ET. That means conditions are favorable for tornadoes and severe thunderstorms.

Tornadoes, hail up to one inch in diameter, wind gusts up to 70 miles per hour and dangerous lightning are possible, the NWS reported.

By 7 p.m., the weather had passed over the District of Columbia without much more than heavy rain at times and wind gusts. But suburbs near the capital saw much heavier action as part of a massive weather system sweeping the East Coast.

A tornado was reportedly spotted in Columbia, Md., part of the Metro D.C. area, and a tornado warning was issued for an area of Montgomery County, Md., a suburb of the city, and funnel clouds had been spotted in the county. Warnings and watches stretched as far west as Kansas, and up into Pennsylvania.

On the National Mall, authorities used loudspeakers to ask Independence Day revelers to clear off the lawns and head to safer locations, including museums lining the National Mall, until further notice.

Families packed their blankets and streamed off the grassy area that was to host a concert by the National Symphony Orchestra and fireworks viewing a few hours later.

The evacuation followed a weather plan authorities had prepared, and was orderly and smooth.

"We planned for this exact scenario, and it went off exactly as we planned," said U.S. Park Police spokesman Sgt. Robert Lachance.

Police weren't forcing people to leave who wanted to stay, but no additional visitors were allowed in through any of the 19 checkpoints.

The scene was almost a repeat of last year, when a severe storm hit the National Mall at approximately the same time and sent people fleeing for nearby buildings and museums.

Security was heightened for festivities in the nation's capital following recent attempted car bombings in Britain. Hundreds of emergency responders from about 20 law enforcement agencies were on duty, authorities said. Officers were urged to be on alert for vehicles with suspicious characteristics such as protruding wires or an unusual odor.

As with past July 4 festivities since the Sept. 11 terrorist attacks, Washington's mall was fenced off and visitors were required to pass through security checkpoints, which opened at 10 a.m.

The evacuated crowds would have to pass back through the checkpoints to get into the area once the storms passed.

Officials were expecting as many as 500,000 visitors to the National Mall for the annual national fireworks display. The annual Capitol Fourth concert, hosted by Tony Danza, and featuring American Idol Elliott Yamin, musicians Yolanda Adams, Little Richard, Dierks Bentley and the National Symphony Orchestra among others, takes place outside the Capitol. Officials were hopeful the inclement weather would pass before the concert's 8 p.m. ET start.

The Associated Press Contributed to this report.