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'Dixie Alley' as dangerous as the better-known Tornado Alley, say scientists

As storms ravage the South, a recent study suggests that Dixie Alley may just be an extension of its better-known neighbor Tornado Alley, putting much of the eastern US at an 'elevated' risk for tornadoes.

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Professor Dixon says the study, published in the Bulletin of the American Meteorological Society in December, grew out of an interest in trying to define what had come to be known as Dixie Alley. It's a kind of southern analogue to Tornado Alley, but one that had received far less scientific scrutiny than its more-famous counterpart.

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If his study is right, it suggests that Dixie Alley is actually just an extension of the classic Tornado Alley. Dixie Alley's assumed individuality stems from a region of relatively low tornado risk between them, near the Ozark and Ouachita Mountains.

For their study, Dixon's team looked at tornado data from 1950 to 2007 gathered by the National Weather Service's Storm Prediction Center in Norman, Okla.

But long-term tornado data are notoriously hard to work with, he and other weather researchers say. Numbers of tornadoes appear to have risen, an artifact of more people living in once-rural areas where few tornadoes were once spotted or reported.

In addition information on a tornado's full track is a relatively recent addition to the data pool. Typically, studies were based on noting where a tornado first touches down.

The team adjusted for the changes in tornado numbers by including the number of "tornado days" – which show no trend up or down over the study period. And they built their approach on looking at the full paths of tornadoes and how often those paths passed relatively close to each other.

Some tornado researchers aren't quite ready to sign off on the approach Dixon's team has taken.

The team's analytical approach may involve too few tornadoes in any one area to yield meaningful statistics, notes Harold Brooks, a tornado researcher with the National Severe Storms Laboratory, also in Norman, Okla.

Moreover, the classic Tornado Alley is distinctive because displays a stronger seasonal feature – most of its tornadoes are spawned in violent spring storms – than Dixie Alley, Dr. Brooks notes. The Southeast has about the same number of tornadoes, but they are more evenly spread out over a year.

Yet Dixon's team maintains that the density and lengths of tornado paths are at least as important for risk assessment as the number of twisters and the times of year they appear.

Given rapid population growth in the Southeast, and the generally longer paths tornadoes there etch across the landscape, the study can provide additional details for assessing tornado hazards in the US in general, and the Southeast in particular, the research team suggests.

"It would not hurt my feelings if in two years or five years, with better data or more advanced statistics, we can show this paper is not valid anymore," Dixon says.

In the meantime, what may be just as intriguing are the areas, within the wider region of elevated risk, where the risk is still relatively low. "I have yet to hear a reasonable explanation for why [those] particular areas" have few tornadoes, Dixon says.


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