The Weather Channel
Tornadoes are one of the most violent and deadly forces of nature. They can strike suddenly and devastate an entire community within minutes.
Before the height of severe weather season had even arrived, 1999 had become a record setting year for tornadoes. In January, a month better known for blizzards and ice storms, a staggering 169 twisters occurred.
The Southeast received the lion's share. On the 17th, nine people were killed as tornadoes raged across Arkansas, Missouri and Tennessee. Over a three day period beginning on January 21, 104 tornadoes touched down from Arkansas to Florida. One of those tornadoes ravaged Clarksville, Tennessee. More than two dozen buildings were leveled in the downtown area. Incredibly, there were no deaths and only a few injuries.
By month's end, 19 people had fallen victim to tornadoes in the United States. January's preliminary total of 169 tornadoes more than triples the previous record of 52 set in 1975.
"Tornadoes during January are not unprecedented," said Stu Ostro, Meteorology Team Leader at The Weather Channel. "What was unusual about the recent outbreaks was the magnitude of the outbreaks, we're talking scores of tornadoes, also the area that was affected was a bit farther north than what would typically be the case in the middle of the winter."
Tornadoes are more likely to strike along the Gulf Coast during the winter. While the number of tornadoes was unusually high this winter, the weather events leading up to them were not necessarily out of the ordinary.
"We've had disturbances coming across the southern part of the U.S. which have resulted in a triggering of thunderstorms with a strong vertical wind shear that we've associated with these disturbances this time of the year. And with the relatively warm, moist air coming up from the Gulf of Mexico the stage had been set a number of times for a lot of tornadoes," said Howard Bluestein, Professor of Meteorology at the University of Oklahoma.
But were those tornado producing weather systems prompted by something greater? La Niña's influence has not been ruled out.
"That's an area thats under a lot of research, how El Niño and La Niña project on extreme weather events," said Antonino Busalacchi, NASA Research Oceanographer, "During La Niña what we have the tendency for, is for these collisions of air masses; dry cold air from the north colliding with moist warm air from the south. When that happens it sort of sets the stage for more tornadoes, but doesn't necessarily mean we can predict exactly or precisely that there are going to be more in a certain region of the country."
"We do think that the recent El Niño and now La Niña have contributed to the locations in which the tornado outbreaks have occurred," says Ostro, "However, tornado formation is a very complex process and by no means have El Niño and La Niña solely determined which communities have been hit."
Forecasters do agree that La Niña makes U.S. weather more variable; however, they can't say if there will be more extreme tornado outbreaks during the remainder of 1999.