Research Indicates that the Significant Tornado Threat is Shifting Eastward - Away From “Tornado Alley”
LAWTON, Okla. (TNN) -
“Tornado Alley” is a staple reference during Spring as severe weather and tornadoes frequent the central United States. There are many different definitions of “Tornado Alley” as a location descriptor, which primarily stem from a personal perspective (Gagan et al., 2010). The term is loosely used to describe the general region in which an above-average occurrence of tornadoes lies, generally describing the Central Great Plains and Southern Great Plains including states like Oklahoma, Texas, Kansas, and Nebraska. Its cousin, “Dixie Alley”, is less notorious and is referenced infrequently in comparison. It includes most of the Southeastern United States, not including southern Florida.
The locations in which tornadoes are frequently observed is a matter of climatological research in which the patterns and frequency of severe weather events are recorded and the trends analyzed. “Tornado Alley” is what most people would argue to be the hot spot for tornado development in the United States, but research acknowledges the shift in this pattern. Most meteorological research does not reference a solidified “Tornado Alley”. It defines the region in the United States where tornado occurrence is increased to be a broad sheath in the Central US from the northern Midwest through the Southeast, including the traditional “Tornado Alley” and “Dixie Alley”. Comparison research between the two regions shows that “Tornado Alley” has a far higher frequency of tornadoes than “Dixie Alley”, living up to its name. Recent evidence has shown that the trend of tornado frequency in “Dixie Alley” is on the rise (Gensini, 2018). Not only is the number of tornadoes increasing, but the parameters for strong and violent tornadoes in the Southeast show that the occurrence of strong tornadoes is comparable to that of “Tornado Alley”, which is alarming considering the lower frequency of tornadoes. While still paling in comparison to the statistics of “Tornado Alley”, there is considerable danger in the current trend in the Southeast.
The nick-names of these regions are a primary source of the misleading nature of their tornadic conditions. The name “Tornado Alley” is blatant and explanatory to the region, whose residents are well aware of the dangers and possibility for frequent tornadoes when arriving due to the notoriety of the region. This is a good thing in that awareness of severe weather occurrence is prevalent and therefore safety preparations are made beforehand. This is problematic for areas in the Southeast as they are not as well known for the tornadic activity that occurs in the region which can be misleading and give way to false security, especially considering the recent trend of increasing tornado production. It is important to note the impact of stereotyping on sociological motivation in emergency management situations. Most people feel as though they are over prepared for disaster, although it is suggested people often overestimate their preparedness (Donahue, 2014). Generalizing the safety of a region can impact this even further due to preconceived security.
There is considerable danger in the increase of tornado frequency when the magnitude and strength of “Dixie Alley” tornadoes is taken into consideration. Studies show that the number of strong and violent tornadoes in “Dixie Alley” is 89 compared to 70 per 10,000 miles, a significant comparison given the lower tornado count in the Southeast (Gagan et al., 2010). This means that although the occurrence of tornadoes is lower, the probability of the tornadoes that do occur being violent and deadly is much higher. This is important when quantifying the increasing frequency of tornadic activity because along with more tornadoes, there will be more strong and violent tornadoes. Threats to major population centers are also increased in the Southeast as compared to the Southern Plains due to the population of the region. Areas like Tennessee, Georgia, and Alabama have much higher population densities than Oklahoma and Kansas, which leads to deadlier tornado outbreaks. One of the other issues that need to be considered is the availability of atmospheric energy in the Southeast as compared to the Plains. The shift moves the tornadic potential into a region that has significant moisture and convective potential. The ingredients that produce supercells and tornadic activity are mainly moisture, warm air, frontal boundaries, instability, and wind shear. These ingredients depend heavily on the location of opposing air masses, which are largely driven by the jet stream. This is where it is crucial to take into account the impacts of climate change on the shifting of tornadic frequency and strength.
Impacts of climate change are subtle but lead to impactful weather events. Climate change has been linked to the variation and weakening in the jet stream, which leads to an increase in significant weather events (Nunez, 2021). One of the impacts from this is a shifting jet stream and wavering polar vortex, or the rotations around the poles, giving way to low dips in the jetstream over the United States. The jet stream provides many of the frontal boundaries that are weather producers, so a southerly dip creates a more southeastward shift in frontal boundary production and subsequently an increase in significant weather events in areas of “Dixie Alley”. The other result of climate change is the strength of the jet stream. With a weaker jet stream, frontal boundaries are not pushed across the United States as quickly, leading to tighter temperature and pressure gradients that provide lift in storm generation. The fronts not only move slower but are stronger and produce enhanced severe weather ingredients.
Tornado frequency in “Dixie Alley” has many different consequences that must be considered. The safety education of the population located in this area is important so that emergency management and storm preparedness can prevent loss of life. The terrain in “Dixie Alley” is also significantly contrasted to the Great Plains. This could contribute to the notoriety of “Tornado Alley”, where large picturesque supercells roll over the flat fields and country. The abundance of trees and hills in the Southeast leads to a precarious situation for rain-wrapped and low visibility tornadoes. Nighttime tornadoes are a common occurrence for severe weather events due to the slow progression of fronts, giving ample time for daytime heating to break the “cap”, a contributing parameter to severe weather (NOAA, 2019). Warning systems are of the utmost importance in these locations, especially given the high population density. The density of mobile homes in the Southeast increases fatality rates, as mobile homes are seen as one of the most dangerous locations in the event of a deadly tornado. The tornado fatality rate is far higher in the Southeastern United States due to these conditions and should be acknowledged with the trend of increasing tornadic activity. The two deadliest tornado outbreaks in recorded history, taking over 200 lives each, were recorded in the Southeastern United States (World Meteorological Organization). Research suggests that tornado frequency will continue to increase in this region, and it is critical that measures are taken to prepare and educate the population.
Donahue, Amy K., et al. “Ready or Not? How Citizens and Public Officials Perceive Risk and Preparedness.” The American Review of Public Administration, vol. 44, no. 4_suppl, July 2014, pp. 89S-111S, doi:10.1177/0275074013506517.
Gagan, John P, et al. “A Historical and Statistical Comparison of ‘Tornado Alley’ to ‘Dixie Alley.’” National Weather Digest, vol. 34, no. 2, Dec. 2010.
Gensini, Vittorio A., and Harold E. Brooks. “Spatial Trends in United States Tornado Frequency.” Npj Climate and Atmospheric Science, vol. 1, no. 1, 2018, doi:10.1038/s41612-018-0048-2.
Nunez, Christina. “Jet Stream Facts and Information.” Environment, National Geographic, 10 Feb. 2021, www.nationalgeographic.com/environment/article/jet-stream#:~:text=Climate%20change%20and%20the%20jet%20stream&text=Slower%2C%20weaker%20jet%20streams%20have,place%2C%20stalling%20them%20over%20regions.
US Department of Commerce, NOAA. “Weather Glossary: C’s.” NWS JetStream, NOAA’s National Weather Service, 14 Aug. 2019, www.weather.gov/jetstream/glossary_c.
World Meteorological Organization. Tornado: Largest Tornado Outbreak | ASU World Meteorological Organization, web.archive.org/web/20130926235427/wmo.asu.edu/tornado-largest-tornado-outbreak.
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