Tracking down tornadoes
Be prepared, not paranoid
By Greg Botelho
CNN
(CNN) -- In a blizzard, two feet of snow won't fall at your house while your neighbor gets a dusting. Hurricanes rarely pummel one part of town and totally skirt another, nor does an earthquake rattle one building and leave one next-door unshaken.
But equality often flies out the window with tornadoes.
Randomness is a key feature of twisters, in which 300 mph-plus winds might devastate one community but spare another nearby. Yet weather experts have become increasingly adept at understanding tornadoes, especially in the twister-prone swath of the Midwest known as Tornado Alley.
Twenty years ago, warnings would only be issued if a "spotter" reported a twister touching down. But thanks to technology like Doppler radar, satellites, weather balloons, computer modeling and climatic and historical studies, authorities now can send out a cascading set of watches and warnings indicating when, where and how strong a tornado will strike.
"In the last five years, we have started honing in on things that help us distinguish tornado-producing conditions," said Harold Brooks, a top researcher at the National Severe Storms Laboratory.
"Putting in Doppler radars and warning systems has reduced the number of fatalities by 40 percent," he noted. "That's 40 lives a year."
Yet tornadoes still command fear, observers note. Some of this stems from true stories, like tossed cars, mattresses flying 40 miles or personal checks floating 125 miles. Fictional tales of twister power -- from movies to local legends to since discredited official pronouncements -- fuel public apprehension.
Based on both history and science, experts say people should be prepared but not paranoid.
"Some time between now and the middle of June, an absolute random choice of town can be ripped to shreds," said Tom Grazulis, director of the Tornado Project, a company that compiles and distributes data about tornadoes. "You have to be ready, even though it's extremely rare -- once in 10,000 years will a tornado hit your neighborhood."
Forecasting challenge
 Twisters can rip apart communities, like this area outside Kansas City, Missouri, after a May 2003 tornado. |  |
To understand tornadoes, one must first understand the thunderstorms that spawn them.
The latter needs warm, moist air at low atmospheric levels, colder temperatures higher up, and something to lift the warm air. Tornadoes arise out of super-cells -- a thunderstorm that rotates, explains Brooks -- which require converging and increasingly strong winds as well as a range of temperatures and moisture on different atmospheric levels.
About 10 percent of the 10,000 or so thunderstorms in the United States each year produce tornadoes, and only 100 to 200 of those are severe -- F2 or greater on the Fujita Scale, which is used to chart twister strength. (A F2 or greater twister causes considerable damage with winds of at least 113 mph.)
"We have tornadoes [nationwide] 180 days a year, every other day, and we have significant tornadoes probably about 60 days a year," said Brooks. "It requires a fairly delicate balance: Even if you have a thunderstorm, you don't necessarily have a tornado."
A tornado's tenuous mix of ingredients, plus its short life span (a few minutes, on average), make it difficult to predict accurately more than a few hours in advance.
Experts rely heavily on "vertical profiling" -- getting data for multiple atmospheric levels, up to 30,000 feet -- to chart the possibility and strength of twisters. Computer modeling, pattern recognition and forecasting experience also come into play.
"Computer models are like a model car: Sometimes they're perfect and work well, but some models don't get it right," said CNN meteorologist Chad Myers, who used to work in Oklahoma City. "Forecasting is both an art and a science, just like medicine isn't an exact science."
Action in the alley
|  A November 2002 tornado in Van Wert, Ohio, tore the roof off a theater and tossed cars into its seats. |
The 2003 tornado season proved just how tricky tornado forecasting can be. After very little activity through late April, usually an indication that the entire year will be fairly calm, a rash of storms made May the busiest month since record-keeping began in 1950 -- 516 tornadoes, shattering the previous mark of 399 set in June 1992.
While tornadoes can strike anywhere and at any time, studies have given meteorologists a good idea of where and when to look for twisters.
"Will every state eventually get a tornado? Yes," said Myers, noting tornadoes also touch down in places like England and Holland. "But certain areas are more prone than others."
An area known as Tornado Alley -- from Louisiana and Texas north to North Dakota and east to Ohio -- regularly has more twisters than anywhere in the world. Mountains to the west, warm moist air from the Gulf of Mexico and cold air from Canada produce conditions ripe for thunderstorms and, thus, tornadoes.
The region from Oklahoma north to the Dakotas tends to have a well-defined tornado season, with most twisters coming on late spring afternoons. In the more southern states, tornadoes more likely arrive on winter mornings.
"If you see a thunderstorm in early May in Nebraska, say, your immediate reaction is the possibility of a tornado," said Brooks, who works in Norman, Oklahoma. "Elsewhere, the seasonal cycle falls apart quickly. It never goes to zero threat, but never gets all that high either."
Myths and reality
A wealth of both information and misinformation exists about tornadoes.
The concept that tornadoes seek out trailer parks but avoid major cities or other areas for geographical or spiritual reasons has no scientific basis.
 A home in Rineyville, Kentucky, sits in a shambles after a powerful May 2003 twister. | |
Some beliefs were once seen as fact, only to be later refuted. For instance, experts once urged residents to open their windows -- to equalize air pressure and minimize damage -- and huddle in the southwest corner of the basement when a twister approached. This was recommended because most twisters move from southwest to northeast.
Both tips have since proven to be misguided.
"More people are killed getting hit by debris than ever get picked up by tornadoes, like Toto in the 'Wizard of Oz'," said Myers. "The best thing you can do is get to a safe zone, as quickly as possible."
While movies like "Twister" have made tornadoes more exciting for some, producing a new wave of storm chasers, others remain "unnecessarily paranoid," said Grazulis.
"You're more likely to be bit by a rattlesnake or killed at a railroad crossing, but those are accepted risks," he said. "Tornadoes are not an accepted risk -- you know where the snakes live or where the railroad crossing is, but you don't know where the tornado will strike."
Even in Tornado Alley, Brooks said, the chances of a twister striking your town are remote all but a few days each year.
"I don't expect people to pay undying attention ... all the time," said Brooks. "But if today is a day when the threat is higher, that's do-able. Then you start to put extra effort into finding out what's going on."
