Ultimate Tornado is a documentary that first aired on the National Geographic Channel on April 12, 2006. It focuses on several unusually violent tornado events that have occurred in the United States, which include the 2004 Attica, Kansas tornado outbreak (F2-F3), the 1995 Pampa, Texas tornado (F4), the Jarrell tornado outbreak (F5), and the 1999 Oklahoma tornado outbreak (F5).
It last examined the possible effects of a theoretical F6 tornado hitting downtown Dallas, Texas, postulating that this would be the worst tornado in history in terms of cost, damage, destruction and loss of life.
References
Ultimate Tornado Wikipedia(Text) CC BY-SA