By Anne Paine, The Tennessean
Tornadoes killed more people in Tennessee than in any other state over the last decade and that includes those icons of twister country: Kansas and Oklahoma.
At least one expert - contrary to a top government scientist - has predicted even more tornadoes as the 2010 twister season ramps up this spring.
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Whichever way the winds blow, Tennessee, along with Missouri, Alabama and Georgia, could continue to hold top slots for the most deaths.
The Southeast has a disadvantage in that tornadoes often hit at night, it's heavily populated, mobile home parks are plentiful, and hills make it difficult to see tornadoes coming.
Greg Forbes, Weather Channel severe weather expert, said indications are that more tornadoes than usual could be coming this year.
"The statistics show that El Nino years have been followed by years with slightly above average numbers of tornadoes - about 9 percent," he said.
El Nino conditions occur when Pacific Ocean waters near the equator warm, as happened this past year. But, so far, any tornadic activity has been less than usual.
"We've gotten off to a very, very slow start for severe weather and tornadoes," Forbes said.
He attributes the fact that only one tornado was seen in the U.S. in February to a colder-than-normal winter. That's the fewest on record for that month, and it was a weak one in California.
As of Thursday, 14 tornadoes had shown up nationwide in March, which is 20 percent of the usual average.
"Things could turn around pretty quickly," Forbes said. "We can't let our guard down."
Tornadoes, which happen worldwide but mostly in the U.S., require complementary temperatures, winds and moisture combinations. When those elements come together in the right mix, one or more funnels can form.
The state's worst tornadoes in recent years came in 2006, when 34 people died and 259 people were injured in Sumner, Davidson, Warren and other counties. In 2008, 31 people died and 152 were injured in Sumner, Macon and Trousdale counties and elsewhere.
A key to the tornadoes' strength is the increasing rotation of winds inside a storm cell - like when a spinning ballerina raises her arms above her head and speeds up almost to a blur.
Cooling of air from rain evaporating around an updraft in a storm cell can make the air denser and the twister faster and more powerful.
Statistics for Tennessee show a large increase in tornadoes since the 1950s - from under 100 to almost 300. But Bobby Boyd with the National Weather Service in Old Hickory believes the numbers are misleading.
"The apparent increases come from improvements in weather radar such as the Doppler radars that were commissioned here in Tennessee back in the 1990s," he said. "It also comes from public awareness, and the proliferation of digital and video cameras, which means that many more small tornadoes are now sighted and tracked."
Tornadoes generally kill more people than hurricanes each year in the U.S, but exceptions happen, as when Katrina hit.
Harold Brooks, research meteorologist with NOAA's National Severe Storms Laboratory in Norman, Okla., doesn't believe El Nino is a harbinger of more tornadoes.
While the phenomenon can bring more heavy rains, particularly on the West Coast, tornadoes are too unpredictable in the grand climate scheme, Brooks said. "It's not possible to foresee anything," he said of ballparking the level of twister activity in future months.
Even the projected effects of climate change don't provide many clues about whether tornadoes or their ferocity might increase in the years to come.
"There may be some hints we're starting to see, but it's not a big enough signal to be confident that anything is happening," Brooks said. "The effect on tornadoes overall is really hard to predict."
A warming planet might be more likely to brew up thunderstorms, but other factors, such as the North and South Poles warming faster than the equator, could reduce the chances of a strong rotation that's the backbone of a twister, Brooks said.
High winds and hail that pelted parts of Nashville briefly on Thursday were a preview of what could come, with May being the month with the highest number of tornadoes nationally, although they can crop up any month.
Spring is Tennessee's prime tornado season, with another burst possible in November.
Metro Nashville spent more than $1 million adding 71 warning sirens since a young man died in Centennial Park when a tree fell on him during a 1998 tornado. Williamson County has 61 sirens and Wilson County 13.
On Feb. 5, 2008, Heather and Charles Bandy and their two sons, age 19 and 20 at the time, crowded behind a staircase in their Lafayette home as a tornado destroyed their residence and killed six people on their road.
Their house is rebuilt, but this time the basement has a tornado shelter.
"It's good to know you've got a place to go," Heather Bandy said. "We could be in the path of it again."
In Gallatin, Jim Hercik's new, three-level home includes a small basement room with 15-inch concrete walls and steel door. The old house belonging to him and his wife had to be torn down after severe damage in the April 7, 2006, tornado that scoured parts of Sumner County.
The shelter, which they've used a couple of times, provides some peace of mind, but there are still questions. "Are we going to have enough warning to use it?" he wondered.
They, like the Bandys, have a weather radio to alert them.
But Heather Bandy has other concerns, too, saying a trailer park across the street and others around the state need shelters on site.
"They should have to have some kind of place to go where they can get out of it," she said.
Trailers tend to be among the most vulnerable structures in the face of high winds that can toss them around like playing cards.
Winds in the strongest twisters can reach 300 miles per hour, and few above ground are safe then.
"If it strikes a location, you're going to almost have to be underground to survive," meteorologist Boyd said.
As Tennessee grows more populated and tornadoes do increasing damage, businesses have been starting up here to build shelters, including reinforced basement rooms, steel safe rooms bolted to concrete slabs and underground burrows. The prices range from about $4,000 up.
Cumberland Garage Builders of Brush Creek, Tenn., is building a 20-room shelter among others in the coming weeks, and has even more calls and orders after tornadoes hit.
Jeff Turner with National Storm Shelters in Smyrna said shelters seem to "sell themselves."
"People are really interested in these things," he said.