4 p.m. Update: The Falcon Virgo exercise has been postponed 24 hours because of the weather.

Original post: Don’t be alarmed if you hear a mass of fighter jets and helicopters in the skies overnight.

The North American Aerospace Defense Command (NORAD) plans to conduct its monthly air exercise, Falcon Virgo, over the Washington region from 12:01 a.m. to 2 a.m. and 4:10 a.m. to 5 a.m. Wednesday.

NORAD has conducted similar exercises throughout the United States and Canada since the terrorist attacks on Sept. 11, 2001.