This story has been given a lot of attention in the Southern media, but while the study is new the information is not. The idea that there is a Dixie "leg" to traditional "Tornado Alley" has been around informally for a couple decades, and formally in the literature since at least 2007. Remember, what a  tornado  occurrence map looks likes depends on the criteria, data, and methodology used n the research study. The latest study was presented at the annual meeting of the American Association of Geography, of which I am a member.

Tornadoes are commonly thought to focus their destruction on "Tornado Alley," a stretch of land that spans Texas and Oklahoma North toward Minnesotta and Illinois. It is a term from the media not from meteorologists. The new research finds that tornadoes actually have several other preferential zones across the eastern United States.

Michael Frates of The University of Akron in Ohio analyzed devastating F3 to F5 tornadoes with tracks of 20 miles or longer that hit the southern and eastern United States from 1950 to 2006 and found three other "alleys," one of which is even busier than the original.

Earlier studies have analyzed tornado distribution by county. Frates instead divvied up the map into grid cells all of the same size, a method that he says provides greater resolution and catches more of the nuances of geography.

Dixie Alley, centered over Mississippi and northern Alabama, beat out Tornado Alley in tornado number, Frates found. Over the 56 years examined, an average of 2.92 tornadoes hit each cell in Dixie Alley, followed by an average of 2.59 tornadoes in each cell of Tornado Alley. Second and third runners-up are Hoosier Alley (Indiana) and Carolina Alley (centered over both Carolinas).

The two top tornado-prone regions have different storm patterns: Tornadoes tend to strike Dixie Alley all year round, while Tornado Alley's peak season is only four months long. Frates would like to incorporate data such as the number of deaths and the amount of property damage caused by tornadoes in the two regions, particularly since warning systems aren't as advanced in Dixie Alley as they are in Tornado Alley. He hopes the new study will make people "more aware that more tornadoes occur in areas other than Tornado Alley." It is significant that tornadoes in "Dixie Alley" tend to be strong and long-lived on the ground for long stretches, and that they are often hidden by rain and/or occur at night. These factors all add to their deadly potential in the South.

Tornadoes spawned by landfalling hurricanes are NOT part of the Dixie leg of traditional tornado alley. Twisters from hurricanes tend to be much weaker, smaller and briefer-- on the ground for short periods of time, and are not usually EF 3 or higher on the Enhanced Fujita tornado scale. The tornado alley/Dixie alley tornadoes are more likely to be the more destructive EF-3 to EF-5 variety.  Detailed maps slide show here..