April 29, 2011
Wind, Not Climate Change, To Blame For Twisters
Experts suggest that the deadly tornadoes that whipped across the South may have been the largest and most powerful ever to be recorded, leaving behind total destruction and a rising death toll.
The increase in tornadoes in the wake of deadly storms should not be mistakenly blamed on climate change, say U.S. meteorologists.
"If you look at the past 60 years of data, the number of tornadoes is increasing significantly, but it's agreed upon by the tornado community that it's not a real increase," Grady Dixon, assistant professor of meteorology and climatology at Mississippi State University, told the AFP news agency.
"It's having to do with better (weather tracking) technology, more population, the fact that the population is better educated and more aware. So we're seeing them more often," he says.
The biggest tornado outbreak on record occurred on April 3-4 of 1974. At that time 147 confirmed twisters touched down in 13 states and claimed more than 300 lives in the United States and Canada, reports the AP.
But April of 1957 resembles the present year, where several days with large numbers of deadly twisters are recorded, says Brooks.
However, April 1957 was more like this year, recording several days with large numbers of deadly twisters, Harold Brooks of the National Severe Storms Laboratory in Norman, Oklahoma, told the Associated Press (AP).
In recent years, improved forecasts and increased awareness by people living in tornado-prone areas have decreased deaths caused by twisters, especially in smaller and more rural regions, reports the AP.
Over 250 have been killed by the tornadoes that ripped through the U.S. south this week. This was the worst U.S. weather disaster in several years, leaving residents and emergency workers sifting through the debris afterwards.
According to David Imy of the National Oceanic and Atmospheric Administration (NOAA), the deadly Wednesday tornadoes were unusual for being "long track." This means that they were on the ground for a longer period of time than usual, and in this case, it rolled across the land for 30 miles (48 kilometers) or more.
Imy told AFP that an average track would last less than five miles.
These stronger-than-usual tornadoes that affected the southern states were actually predicted from examining the planet's climatological patterns, specifically those related to the La Nina phenomenon.
La Nina occurs when the water in the tropical Pacific Ocean is unusually cool, leading to changes in weather patterns around the world. According to the federal Climate Prediction Center, the La Nina effects are weakening, but could still continue to affect weather for several months.
"We knew it was going to be a big tornado year," says Imy. However, the key to the prediction was not due to climate change, instead, "It is related to the natural fluctuations of the planet."
A particularly strong and deadly storm tore through the heart of what is known as the tornado-prone corridor where the states of Arkansas, Oklahoma, eastern Texas and northwest Louisiana meet, notes Kristina Pydynowski, a senior meteorologist at the AccuWeather.com website.
The storm met much warmer air that arrived from the south over the tropical Gulf. The combination of winds at different altitudes created "significant twisting motion in the atmosphere, allowing the strongest thunderstorms to spawn tornadoes," Pydynowski told AFP.
The U.S. south's "Tornado Alley" twisters are formed when strong jet winds bring upper-level storms from the north to interact with the very warm, humid air mass that comes from the Gulf of Mexico, says David Imy of the NOAA Storm Prediction Center in Norman, Oklahoma.
The U.S. eastern seaboard does not see the same kind of mixture, and the rough weather in that region this week would not have also created tornadoes, at least not on the same scale, Pydynowski said.
Traditionally, the north-south region of the nation from the Dakotas to Texas is seen as tornado-prone, but a second area exists for twister activity that extends across the South from Arkansas to Georgia, known as the Dixie Alley.
Mississippi State University professor Grady Dixon does not differentiate the two areas, arguing that they are really one big tornado risk area.
While that's traditionally seen as a north-south swath of the nation from the Dakotas to Texas with a second twister center "” Dixie Alley "” extending across the South from Arkansas to Georgia, Dixon argues they are really one big tornado risk area.
The near record number of tornadoes reported, did indeed sweep across both "alleys" this month.
Craig Fugate, administrator of the Federal Emergency Management Agency (FEMA) told the French news agency, "Many people think of Oklahoma as 'Tornado Alley' and forget that the southeast United States actually has a history of longer and more powerful tornadoes that stay on the ground longer."
"Actually what we're seeing is springtime," Fugate says, dismissing claims of climate change as a factor in the deadly twisters.
May is historically the busiest month for tornadoes, however, the AP reports that as warm weather begins to set in and dry western air hits the warm moist conditions moving from the Gulf of Mexico, we could see a surge in April.
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