Dry autumns and winters may lead to fewer tornadoes in the spring

June 25th, 2009 - 2:47 pm ICT by ANI  

Washington, June 25 (ANI): A new study by researchers at the University of Georgia, US, has determined that global warming may mean dry autumns and winters that may lead to fewer tornadoes in the spring.

The study pins down, possibly for the first time, how drought conditions in an area’s fall and winter may affect tornado activity the following spring.

The study is specific to Georgia and the Southeast, but further study could reveal patterns that might make this more general, including the already tornado-prone Great Plains.

“Our results suggest that there is a statistically significant reduction in tornado activity during a tornado season following drought the preceding fall and winter,” said Marshall Shepherd, a meteorologist and lead author of the study.

On the other hand, wet autumns and winters examined in the study had nearly twice as many spring tornado days as drought years did.

The research gives hope that one day meteorologists and climatologists may be able to predict the severity of a spring tornado season the way they now do for hurricanes.

The genesis for the research was the severe Atlanta tornado in March 2008, and Shepherd’s interest in how tornadoes form during severe drought years.

To help understand how fall and winter weather might affect spring tornado seasons, the research team acquired the historical database of severe thunderstorms and tornado occurrences from 1951-2006 from the Storm Prediction Center of the National Oceanic and Atmospheric Administration.

They also analyzed storm data reports from the National Climactic Data Center and meteorological drought conditions using historical rain gauge and Tropical Rainfall Measuring Mission (TRMM) satellite data from the National Aeronautics and Space Administration (NASA).

Using a number of tools of scientific analysis, the team primarily focused on tornado activity from March-June in Georgia and the Southeast. What they found was shocking, Shepherd said, yet plausible.

On average, wet autumns and winters presaged nearly twice as many spring tornado days in the study area as prior drought seasons.

Springs following wet winters and falls were also five to six times more likely to have multiple tornado days than antecedent drought years.

“We do not suggest that soil moisture or precipitation the previous fall and winter exert a direct control on which individual storms will spawn tornadoes,” said Shepherd. “But these long-term seasonal relationships in the study area are striking,” he added. (ANI)

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