During the peak of afternoon rush hour on 24 September 2001, an uncommonly strong tornadic supercell thunderstorm traveled across heavily populated portions of the Washington DC metropolitan area. This supercell produced an F3 tornado that tracked across the University of Maryland College Park campus killing two students and injuring 50 others. Damage produced by tornadoes generated by this supercell have reached $100 million. No tornado rated F3 or higher had struck within the Washington Capital Beltway in more than 75 years. Also noteworthy: this supercell, produced an F1 tornado which passed within 0.5 km or less of the Pentagon, the Jefferson Memorial, and the Washington Monument. Earlier this same afternoon, another supercell produced an F4 tornado (the “Rixeyville” tornado), in north-central Virginia, southwest of Washington, DC. These two supercells combined to produced a total of five tornadoes with path lengths ranging from 10 to 30 km long and rated F3 (MD area) and F4 (Rixeyville). Both supercells were classified as “low-topped” (less than 12 km in vertical depth).

This paper focuses first on the meteorological environmental factors that led to development of supercell thunderstorms on 24 September 2001. Second, radar analysis of the tornadic supercell that tracked across the Washington DC region will be provided. Of particular interest in this case is the importance of rapid tornadogenesis due to the apparent interaction of a narrow band of rain showers with the supercell. Finally, factors involved in the warning decision-making process will be briefly reviewed.