Extreme Weather- Nashville, TN

Weather Gone Wild

By Peter Miller

Photograph by Sean R. Heavey, Barcroft Media/Landov

The weekend forecast for Nashville, Tennessee, called for two to four inches of rain. But by the afternoon of Saturday, May 1, 2010, parts of the city had seen more than six inches, and the rain was still coming down in sheets.

Police, fire, and rescue teams were dispatched in boats. One crew in a skiff headed out to I-24 to pluck the driver of an 18-wheeler from the chest-high water. Other teams pulled families off rooftops and workers from flooded warehouses. Still, 11 people died in the city that weekend.

Over at NewsChannel 5, the local CBS station, meteorologist Charlie Neese could see where the weather was coming from. The jet stream had gotten stuck over the city, and one thunderstorm after another was sucking up warm, humid air from the Gulf of Mexico, rumbling hundreds of miles northeast, and dumping the water on Nashville. 
When the sun came out on Monday morning, parts of Nashville had seen more than 13 inches of rain—about twice the previous record of 6.6 inches set during Hurricane Frederic in 1979. 

What’s going on? Are these extreme events signals of a dangerous, human-made shift in Earth’s climate? Or are we just going through a natural stretch of bad luck?

The short answer is: probably both. The primary forces driving recent disasters have been natural climate cycles, especially El Niño and La Niña. Scientists have learned a lot during the past few decades about how that strange seesaw in the equatorial Pacific affects weather worldwide. During an El Niño a giant pool of warm water that normally sits in the central Pacific surges east all the way to South America; during a La Niña it shrinks and retreats into the western Pacific. Heat and water vapor coming off the warm pool generate thunderstorms so powerful and towering that their influence extends out of the tropics to the jet streams that blow across the middle latitudes. As the warm pool shifts back and forth along the Equator, the wavy paths of the jet streams shift north and south—which changes the tracks that storms follow across the continents. An El Niño tends to push drenching storms over the southern U.S. and Peru while visiting drought and fire on Australia. In a La Niña the rains flood Australia and fail in the American Southwest and Texas—and in even more distant places like East Africa.

http://ngm.nationalgeographic.com/2012/09/extreme-weather/miller-text