Watch: Rare shelf cloud seen over Maryland amid severe weather

A dramatic shelf cloud loomed over Bowie, Maryland, as the US Weather Service issued a thunderstorm watch.

The rare cloud formation that forms along the foremost edge of a thunderstorm's gust front signals intensifying conditions.

An eyewitness captured the striking moment as the sky darkened and winds picked up. Video also shows flash flooding hitting Washington DC and Massachusetts because of storms in the Northeast US.