What’s Behind 2011’s Deadly Tornado Season?
Is the frequency of tornadoes increasing?
April certainly had historic tornado tallies, Brooks says, but May does not stand out when you look at the number of tornadoes. Tornado outbreaks on May 24 and 25 have brought the month’s total close to average levels, but “until then, May was one of the slowest months on record,” he says.
What stands out most about this year’s twisters is the number of deaths. But Brooks says there’s no evidence that in the long term, tornadoes are becoming more frequent. Our perception of the frequency of tornadoes is skewed, he notes, because we naturally focus only on storms that have a large human impact. For example, the tornado that touched down in Joplin, Mo., on Sunday, killing at least 125 people, wasn’t a statistical outlier. In fact, it came on a day with fewer-than-average tornadoes.
“If that tornado was five miles north or five miles south, no one outside the meteorological community would have noticed,” Brooks says.
It seems like urban areas are being hit especially hard this year. Is this part of a trend?
Birmingham, Ala., Tuscaloosa, Ala., and Joplin were all hit this year. But that’s not evidence that tornadoes are becoming more common in cities, Brooks says. A tornado struck downtown Nashville, Tenn., in 1998, another Oklahoma City in 1999. Most major cities in tornado-prone states have seen some tornado activity over the past century.
“We tend to have a short-term memory,” Brooks says. Current tragedies loom larger than historic events.