Tuesday, April 13, 1999

Some see '99 as a peak year for tornadoes

La Nina's effect could be a warning

The Cincinnati Enquirer

        Tornadoes are as unpredictable as they are deadly and it makes forecasting them through the spring and summer storm season difficult, national weather experts say.

        “Tornadoes are hard to predict,” said Dave Imy, meteorologist with the Storm Prediction Center in Norman, Okla. “Unlike a hurricane, it's a small-scale weather effect.”

        There's a split of opinion among professional storm forecasters about the impact of this year's La Nina effect in the Pacific Ocean and whether it will mean more tornadoes for the nation.

        Meteorologists describe El Nino as an unusual warming in the eastern Pacific Ocean. It eased last spring, but only after triggering disastrous weather around the world for more than a year. Instead of returning to normal temperatures, however, the Pacific cooled drastically. That is known as La Nina. Under that weather system, the subtropical jet stream pushes warm, moist air farther north in America.

        Some weather experts say that can supply the conditions to build severe thunderstorms and tornadoes.

        But Mr. Imy said there is not enough data linking La Nina to increased frequencies in tornadoes. While Friday's killer tornado was horrific, he said, it was not unusual for the Ohio River Valley.

        “These kind of tornadoes don't occur every year, but they do occur periodically,” he said.

        Brian Coniglio, a meteorologist with the National Weather Service, agreed. He said more studies have to be done on La Nina and its subsequent climatological effects before linking the oceanic phenomenon with tornadoes.

        “I don't think anybody can make accurate predictions,” said Mr. Coniglio.

        A Purdue University study, however, contends that Ohio is among 10 states that could experience more tornadoes this year than last because of La Nina.

        Ernest Agee, a professor of atmospheric sciences at Purdue, said Ohio — as well as Arkansas, Indiana, Kentucky, Mississippi, North and South Carolina, Tennessee, Virginia and West Virginia — could see more tornadoes because of La Nina.

        Mr. Agee said the findings are based on a study done by Suzanne Zurn-Birkhimer, a Purdue graduate student who looked at tornadoes over an 81-year period, comparing El Nino with La Nina years.

        States in the Midwest and Ohio and Tennessee valleys had more tornadoes during La Nina years.


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