Trail of deadly storms brings drive for better prediction of twisters
A wave of tornadoes that killed least 12 people this week has people wondering if there could be a repeat of last year, one of the deadliest tornado seasons on record.
A wave of tornadoes that plowed across six states Tuesday and Wednesday, killing at least 12 people, has rekindled memories of the deadly, costly outbreaks in the Midwest and Southeast last April and May.
Last year was one of the worst on record for U.S. tornadoes, in the number (more than 1,700) and deaths (550), a fact driving increased interest in trying to predict how many tornadoes to expect this year. Forecasting firms AccuWeather and Telvent DTN have made predictions, and Columbia University's International Research Institute (IRI) for Climate and Society has even published a new technique for developing seasonal tornado forecasts.
AccuWeather predicts above-average tornado numbers this year, but not as many as in 2011. The company says warmer-than-normal Gulf of Mexico water will provide the moist, unstable air to energize thunderstorm development and help spin off tornadoes.
On the other hand, AccuWeather notes the climate pattern called La Niña is forecast to weaken after generating an unusually strong northern jet stream that fueled the violent storms of 2011.
Telvent meteorologist Jeff Johnson, however, contends even a weak La Niña will influence tornado activity. "As we head toward the spring season, our expectations are that 2012 will favor above-normal tornado numbers once again, primarily due to La Niña," he wrote in a recent blog post.
At IRI, lead researcher Michael Tippett and colleagues have published a new tornado-forecasting method that may provide about a month's lead time on expected activity. Using historical data, his team identified two weather variables most associated with tornadoes — rain and spin in the atmosphere — and created an index that can be put into a model to make forecasts.
In tests, the model "was able to use the index to forecast monthly tornado activity with some success up to a month in advance. This success, especially notable in June, is the first evidence for the predictability of monthly tornado activity," IRI noted in a news release.
Other climate experts cautioned that the conditions that spawned this week's outbreak aren't unusual at this time of the year, and that higher-than-average temperatures aren't to blame.
"One system doesn't make a trend," said Greg Carbin, a meteorologist at the National Weather Service storm-prediction center in Norman, Okla. "In March and April, we'll see an increase in severe weather."
Over 24 hours Tuesday and Wednesday, tornadoes were confirmed in Nebraska, Kansas, Missouri, Illinois, Indiana and Kentucky, killing at least nine people, injuring dozens and destroying homes and businesses.
The hardest-hit town was Harrisburg, Ill., about 100 miles southeast of St. Louis. At least six people were killed in the city of 9,000. The Category EF-4 tornado, the second-most powerful kind on the Enhanced Fujita (EF) scale measuring wind speed and damage, was 200 yards wide with winds up to 170 mph, scientists said.
More than 300 homes and 25 businesses were destroyed or damaged, according to the Saline County Sheriff's Office.
Another tornado hit the country-music resort town of Branson, Mo. At least three people died in southwest Missouri.
The Branson twister seemed to hopscotch up the city's main roadway, moving from side to side, according to witnesses.
"Every time the tornado hit a building, you could see it exploding," said Derrick Washington, who stepped out of his motel room just as the twister began to roar.
The Legends Theater, the Andy Williams Moon River Theater and the Branson Variety Theater all were seriously damaged. The Veterans Memorial Museum was in shambles, and a small military jet that sat in front of the museum was blown apart.
Tornadoes of note also touched down in Harveyville, Kan., southwest of Topeka; near Elizabethtown, Ky., about 50 miles south of Louisville; and in western Nebraska. No deaths were reported.
The National Weather Service noted that the western Nebraska tornado was the first ever reported in that area of the state.
The storm system moved eastward Wednesday and Wednesday night, the National Weather Service said. Powerful storms in eastern Tennessee late Wednesday tore roofs from buildings, flattened trees and reportedly killed at least three people. Authorities said teams would investigate Thursday to determine if tornadoes were involved.
Thunderstorms, high winds and tornadoes also were possible in eastern Kentucky, northern Mississippi and western North Carolina.
Emergency-management officials in tornado-affected states said it was too early to know whether damage warranted a request for federal help. The governors of Kansas, Missouri and Illinois declared state emergencies and would need to request federal-disaster declarations from President Obama to receive assistance from Washington, D.C.
A Federal Emergency Management Administration spokeswoman said the agency is in contact with state officials and is ready to provide help if requested.
Chip Konrad, director of the Southeast Regional Climate Center in Chapel Hill, N.C., said conditions were just right for the storms, with warm, moist air from the Gulf meeting the jet stream at the right point to create havoc.
Konrad said such conditions are tough to predict a week out because several factors have to come together quickly to produce strong storms and tornadoes.
The deadly tornadoes of last year may be fresh in people's minds, but Konrad cautioned against jumping to conclusions about the months ahead.
"Last year really stood out," he said. "But just because it happened last year doesn't suggest it's going to happen this year. We'll have to wait and see."
Compiled from McClatchy Newspapers, The Washington Post and The Associated Press