Once upon a time, some people thought cities might be relatively immune from a tornado's terrors due to the obstructions thrown up by tall buildings, or the microclimates created by urban heat islands — but no more.
The widespread devastation suffered in Joplin, Mo., over the weekend served as ample evidence that those urban legends are mere legends. Meteorologists say that human-made structures — whether they're skyscrapers or mobile homes in a trailer park — are not a determining factor in dictating the path of a violent storm. If it seemed as if tornadoes rarely hit the downtown areas of cities in the Southern, Midwest and Plains states, that was merely because those urbanized areas were so small compared with the open spaces in those regions.
However, that situation is changing. As the population grows and cities spread out wider, that provides bigger targets for tornadoes to hit. "We have people where there used to be farmland," AccuWeather meteorologist Mark Paquette told Reuters.
Paquette said the huge toll from the Joplin tornado was due to bad luck — or, to put it another way, an unfortunate spike in the statistical distribution of storms. "Sometimes you have tornadoes that hit in the cornfields of Kansas or Nebraska or Iowa, and the only person affected is that farmer and it doesn't even hit his house. But here we have a tornado that hit a hospital," he said.
Howard Bluestein, a meteorology professor at the University of Oklahoma, told MSNBC that "it's very unusual for these storms to go through a heavily populated area like Joplin."
"It's a real tragedy that the tornado just didn't go right outside and skirt the city," he said.
Bluestein said population growth, with its accompanying suburban sprawl, has created more areas where tornadoes could cause serious damage. "Cities and suburbs have expanded," he noted, "and there's a higher probability that people will actually get struck."
Joshua Wurman, president of the Colorado-based Center for Severe Weather Research, told Reuters that the tornado could have been worse if it hit an even more populated urban area, such as the Chicago suburbs.
"A tornado doesn't really care what's underneath it," Wurman said.
Meteorologists at the National Oceanic and Atmospheric Administration's Storm Prediction Center keep up a list of selected urban tornadoes going back more than a century. Based on the current fatality figures, the Joplin tornado ranks No. 3 — behind the 1953 tornado that tore through downtown Waco, Texas (114 deaths) and an 1896 St. Louis twister (255 deaths).
One of the center's meteorologists, Roger Edwards, says in an online Q&A about tornadoes that a storm outbreak in the Dallas-Fort Worth metropolitan area during rush hour could result in "staggering death tolls in the hundreds or thousands, and overwhelmed emergency services."
The good news is that tornado prediction methods are improving, even as the potential targets are getting bigger. Thirty years ago, forecasters could provide an average of only three minutes of warning before a tornado hit, Wurman told Reuters. Now the average is 13 minutes.
"We'd like to get that up to 30 or 40 minutes," Wurman said. He said he'd also like to reduce the false-alarm rate for tornado warnings from its current 70 to 75 percent.
And what about climate change? Could global warming affect the frequency or severity of tornadoes? Meteorologists are reluctant to make a connection between tornadoes and long-term, worldwide climate trends, but they do note that this year's La Nina weather pattern in the eastern Pacific could be contributing to the woes in the tornado zone. For more about that, check out this report from Miguel Llanos, my colleague at msnbc.com.
More on tornadoes:
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