by jeff-7058 » Mon May 10, 1999 8:54 pm
La Nina, the weather phenomenon behind record snow in the Northwest this winter and dry conditions in Florida, is . being blamed for influencing the deadly tornadoes that swept across the Plains this week. . ``The signal is there,'' said Steve Byrd, science officer for the National Weather Service in Omaha, Neb. . ``The incidence of tornadoes on the central Plains is slightly higher during La Nina.'' . La Nina refers to a large, unusually cold pool of water in the equatorial Pacific Ocean that develops every several . years, and influences weather patterns around the world. . It works in reverse of the more common and better-understood El Nino, which is a warming of Pacific waters. . La Nina has generated a stronger, colder jet stream in the upper atmosphere, while warm, wet air at lower levels has . been pulled from the Gulf of Mexico into the Plains states. . This combination generated the ferocious thunderstorms that spawned dozens of twisters, including a historic F-5 . tornado in Oklahoma City. An F-5 is the most powerful tornado there is. At least 41 people have died in Oklahoma . alone as the result of the severe weather. . The current La Nina has persisted for nearly a year, fueling weather that resulted in 91 feet of snow on Mount Baker . in Washington this winter and severe drought in Florida. Most La Ninas last only several months, and there are signs . that this one is beginning to wane. . The weather pattern comes on the heels of an El Nino that dissipated in 1998. Studies suggest tornadoes were . reduced by as much as 24 percent in some regions during the most recent El Nino. . El Ninos increase storm activity in California and South America while calming things down in the Atlantic and . Caribbean. La Ninas, by contrast, reduce storms in California but stir up trouble in other parts of the country as well . as in India and southeast Asia. . This spring, meteorologists in Nebraska and Iowa already have tallied 17 tornadoes _ five more than normal by early . May. ``We're already living up to predictions,'' Byrd said.