A few weeks ago, I visited two small towns that hold unwanted places in the annals of bad weather: Greensburg, Kansas, devastated by an EF5 tornado on May 4, 2007, and Moore, Oklahoma, hit by another EF5 tornado on May 20, 2013.
Both towns lie in what is called Tornado Alley, a sprawling region of the Great Plains of North America, where more tornadoes are spawned than anywhere else on the planet. The meteorological ingredients there are just right for such storms, for there cold air moving south from the Arctic meets warm, moist air swirling up the east flank of the Rocky Mountains from the Gulf of Mexico, producing violent clashes of air masses that engender large raindrops, what seem to be a necessary ingredient for tornadoes. Not all of these storms, of course, are of the EF5 category, whose members involve air movement of more than 200 miles an hour, but enough of them are that in tornado season, especially in late spring, weather watchers keep an anxious eye out on the skies over Kansas, Oklahoma, and northern Texas.
It’s a little surprising, perhaps, that more supercell storms visit the Denver metropolitan area than elsewhere on the Plains, while Florida and the Mississippi River delta, which also lie outside Tornado Alley, rank higher than Oklahoma City in the likelihood of the supercell storms that spawn tornadoes. Yet the storms that run in a broad belt that includes such population centers as Wichita, Kansas City, Oklahoma City, and Dallas seem to be causing more destruction than ever these days, in part because those storms may be intensifying overall, and in part because older buildings and infrastructure cannot stand up to them, in which case people are all too often injured or killed.
Our knowledge of tornadoes is improving, as well as our ability to predict them, thanks in good part to research at the National Weather Service Storm Prediction Center, headquartered in Norman, Oklahoma, just a few miles from Moore. Even so, because such storms are dynamic and quick to develop even under predictable conditions, tornadoes often arrive with only a few minutes’ warning.
It’s for that reason that people who live in areas of danger are encouraged to build and maintain strong storm shelters, typically of reinforced concrete. Many new homes in the area come with such structures, and they figure prominently in the remade cityscape of Greensburg. Other measures can be taken in the event that a person is caught in a storm without access to such a shelter. Stay away from windows, keep low to the ground, and protect your head if possible.
Tornadoes are hardly confined to Tornado Alley; indeed, at one time or another, every one of the American states and most Canadian provinces have seen tornadic activity, and tornadoes have been seen on every continent save Antarctica. Even so, obviously, some places are more dangerous than others. The United States sees more than 1,000 a year, but nearly half of the country sees tornadoes only once every five years, if at all. Only a small portion of the country, including much of the region of Tornado Alley, is statistically likely to see two or more tornadoes in any given year—but that small portion of the country suffers disproportionately.
Greensburg and Moore were unfortunate victims, along with recent scenes of devastation such as Joplin, Missouri, and El Reno, Oklahoma, where three well-known “stormchasers” were recently killed. All those places are slowly returning to normal—with the understanding, always, that the skies above can become dangerous at any moment.