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Are tornadoes becoming more frequent, or are they just easier to spot?

4:11 PM, Sep 10, 2013   |    comments
The EF5 tornado that ripped through Moore, OK is probably the defining moment of what has otherwise been a fairly calm year for severe weather.
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So far, 2013 has been a pretty calm year for tornadoes. It might not seem that way, because of the disasters in the Oklahoma City area in May, and our own tornado outbreak in the DMV back in June. But, surprisingly, this year's tornado count is actually below average. This is illustrated in the graph below, which I got from the Storm Prediction Center's website. 

Tornado counts, based on local storm reports from weather offices around the country

As you can see, the tornado count is below normal, and it's also way below the count for 2011, which was arguably the worst year for tornadoes in American history. Here's a map of the tornado reports for 2011: 

2011 tornado reports, courtesy of NOAA. Triangles are color-coded for a tornado's 

strength; lines indicate long-track tornadoes.

In comparison, the tornado reports were a lot sparser 50 years earlier. 

1961 tornado reports, courtesy of NOAA. Triangles are color-coded for a tornado's

strength; lines indicate long-track tornadoes.

Tornadoes are reported via eyewitness accounts by trained storm spotters, and/or through rotation signatures on Doppler radar. Tornadoes are then confirmed via damage assessments, relying on a path of destruction to determine if a funnel touched down. So here's the problem-- how do we know that 2011 was the worst year for tornadoes? There are a few factors that should be taken into consideration. 

Not as many people lived in the Midwest and the Plains states in 1961 than in 2011, so there were fewer people who could potentially see a developing funnel. More people means more buildings, so it's also possible that it's easier to see and assess tornado damage now than it was 50 years ago, simply because there are more buildings and structures that could be damaged by the storm's winds. 

Technology improvements are a big factor. In 1961, the weather radar was primitive compared to the tools we have today, and 1961 also happens to be the year when the first weather satellite was launched into space. Before then, we could not look at storm systems from above. (I can't even comprehend what it was like to make a forecast without looking at satellite data!) 

Finally, it has occurred to me that the "interest factor" should not be ignored! As technology has improved and weather coverage has expanded in the media, people's interest in the weather has skyrocketed. The phenomenon of the storm chaser is not new, but its recent popularity has led to a huge increase in the number of storm spotters and other people who follow thunderstorms in anticipation of a developing funnel. The increased number of tornadoes could be partially attributed to a larger number of trained storm spotters, amateur weather watchers, and everyone in between!