Explainer: What are the trends with tornado occurrence and strength?

Published: Apr. 7, 2021 at 5:50 PM EDT
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TALLAHASSEE, Fla. (WCTV) - The last few years have been busy with severe weather and tornadoes in the Big Bend and South Georgia. Examples include the tornado outbreak on April 23, 2020 where a tornado hit northern Tallahassee, and another outbreak spawned a twister in Cairo, Ga. on March 3, 2019.

Is there a trend with tornado frequency and strength in not just the viewing area but also the United States?

For frequency, it appears that there hasn’t been a noticeable change in the U.S. since 1950 according to data pulled by Carbon Brief.

But research published in 2014 found that there are more clustered tornado events. In other words, there were more tornadoes in one particular day instead of spread out over time.

Research also found that there may be an increase in tornado power. A study published in 2019 from the Florida State University Department of Geography found that the power of tornadoes has increased 5.5% per year since 1994. Dr. James Elsner and the FSU coauthors also found that the higher power occurred during La Niña phases, from November through April and during the overnight hours.

It’s important to note that “power” used in the Elsner et al. study is not the same as the Enhanced Fujita (EF) scale. The EF scale is used to determine a tornado’s strength based solely on damage that a tornado produces. But there has been a slight uptick with higher-damage-producing tornadoes in the viewing area.

The graph shows significant (EF-2+) and sub-significant (EF-0 to EF-1) tornadoes in the...
The graph shows significant (EF-2+) and sub-significant (EF-0 to EF-1) tornadoes in the Tallahassee television market (plus Liberty and Franklin counties) between 1996 and 2019.(Charles Roop / WCTV)

Since 1996, there has been a slight increase in EF-2 and stronger tornadoes in the WCTV viewing area while a slight decrease in weaker tornadoes according to data pulled from NOAA’s Storm Events Database. Tornado events from 2020 were not included since that year’s database was incomplete as of Monday. Tornadoes prior to 1996 were not included since research has found discrepancies with tornadoes reported before and after the use of Doppler radar - specifically with tornado-spawned tornadoes in Florida.

It’s worth noting that the tornado the above graph only covers just over two decades, and twisters before 2007 were rated on the old Fujita scale.

There is difficulty with getting a good scope on longer trends with tornado activity - especially with the subject of climate change. Since there is still a lot of learning left to do with tornadoes, confidence in attributing trends with climate change is low - for now. The below tweet featured in a piece from meteorology professor Dr. Marshall Shepherd pointed out that issue.

But there is the potential of more convective energy as the world warms according to a few studies (such as this one).

There has been a notable geographic shift of tornadoes in the United States in recent decades, according to research published in 2018. Places like Texas and Oklahoma have seen fewer tornadoes between 1979 and 2017, but more have formed in the Deep South. There was also a statistically significant shift to parts of the Florida Panhandle and South Georgia during the winter months.

Whatever the trends are over time, it’s important to be have a way to be warned and know what to do when tornadoes threaten the area.

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