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| S P E C I A L | El Niño Returns |
El Niño may weaken spring tornadoes
El Niño may reduce the severity of the tornado season in certain areas By Environmental News Network staff
El Niño, the weather phenomenon blamed for Florida's recent killer tornadoes, may actually benefit the Lower Plains and parts of the South during the imminent spring tornado season, according to a graduate student at Mississippi State University.
William Monfredo, who has been busy studying 40 years of accumulated weather data, is predicting a decrease in the frequency of strong and violent 1998 season tornadoes -- those rated 2-5 on the Fujita scale -- for the central United States.
"El Niño won't worsen our tornado season," Monfredo said. "In fact, it may even make it milder."
The national tornado season is February-July and usually peaks in the spring.
Monfredo obtained much of his data from weather balloon recordings. After analyzing the information with a statistical model, he determined that wind speed and direction were inconsequential factors. "Cap strength" is another matter, however.
The cap is the layer of air that forms between the warm, moist air nearest the Earth and the very warm and dry air above the layer. Its strength and thickness are determined by the air above and below. Monfredo said he believes that "cap strength" is the key to the milder El Niño tornadoes.
"The stronger the cap, the longer it takes for building clouds to break through into the upper atmosphere," he explained. "The resulting storms and tornadoes traditionally are more violent than usual."
Monfredo said he believes El Niño -- the periodic warming of Pacific Ocean waters -- will cause this spring's cap to be "weaker and less frequent."
"While the southern low Plains should see fewer strong and violent tornadoes, the mid-South region, the area most strongly affected by the results of El Niño, should benefit the most," he said.
David Arnold, assistant professor in the geosciences department and director of the department's climatology laboratory, said Monfredo "is the first to discover this link between cap strength and El Niño."
Copyright 1998, Environmental News Network, All Rights Reserved
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