Science Sunday: Is Tornado Alley Shifting East?

If you’ve lived in the Tennessee Valley for any length of time, especially over these last few years, you’d know firsthand that this portion of the country is no stranger to severe weather. Per the local NWS statistics dating back several decades, the combined warning areas of the Huntsville and Nashville NWS offices has seen 1,000+ tornadoes since records began – with numbers like this, you may be asking yourself why we’re never considered traditionally a part of “Tornado Alley”. But with new research over the last several years done by Victor Gensini and collaborators at Northern Illinois University, the old notions of where that so-called Alley truly lies is changing fast.

Throughout much of this countries history (and indeed through much of my own life), you’d typically find that most people consider the Great Plains to be the heart of “Tornado Alley”. As a kid in Oklahoma, some of the defining features of life in Oklahoma were the Wednesday siren tests, the school fundraisers for storm shelters, and watching Gary England or Mike Morgan for warnings when severe weather came knocking. By all accounts, this answer to the question of where “Tornado Alley” is worked for the longest time – after all, in the last 25 years, Oklahoma has seen several F5/EF5 rated tornadoes, and the gorgeous dancing rope-like tornado photos that make headlines almost always stem from places like Kansas, Oklahoma or Texas. But in those same recent years, some of the deadliest and most damaging tornado events have occurred in a portion of the country that typically has been excluded from this so called Alley – the Southeastern US.

All it takes is looking back 12 years to see the most recent morbid example of this. There is a good reason that many Alabamians shiver when they hear “April 27th, 2011” in conversation. In one day, the state experienced 62 tornadoes – 140% more than the state would usually see in an entire year, on average – and unfortunately lost 252 men, women, and children to eight EF4s and three EF5 tornadoes throughout the afternoon. This outbreak is often considered one of, if not the worst outbreak in recorded history. The only reason it isn’t is due to another outbreak – one that took place in almost all of the exact same places – 37 years prior in 1974. The southeast being host to essentially all of the largest tornado outbreaks in history may on it’s own be a reasonable (if slightly morbid) cause for inclusion when discussing “Tornado Alley”, but recent tornado numbers and climate trends may be indicating that the old notions of where the greatest tornado threats lie are fading fast.

Since the beginning of the 1990s, it has been found that “tornado days”, or days which see 1 or more reported tornado in a given area, have trended higher east of the Mississippi River and into the Tennessee Valley and have actually trended downwards across much of the traditional “Tornado Alley”. Moreover, days with high “Significant Tornado Parameter” values – a tool used in forecasting to help diagnose the likelihood of significant tornadoes – have increased in the Tennessee Valley and MS Delta region, and once again have trended downwards across portions of Oklahoma, Kansas, and Texas. While this doesn’t mean the old “Tornado Alley” should be excluded from it’s traditional geographic classification, the implications of these statistics paint a concerning picture, and for more than one reason. For one, consider the fact that, in our region, tornado season can broadly be considered to be November – April; in contrast, the plains have a several month maxima throughout the Spring and Summer months. This may seem like an innocuous distinction at first, but keep in mind how little daylight we see in this time frame, and that the most common hours for tornadoes are well past sunset in the Southeastern United States.

Frequency trends from 1989 - 2019. Credit: Gensini/Brooks, 2018.

Likewise consider the standards of living – compared to the Plains, the Southeastern United States on average has triple or more the amount of residential mobile homes in comparison to site-built, foundation-laid homes. You may hear it often from our own Fred Gossage during tornado coverage – mobile homes make fantastic affordable housing and he himself lived in one for a large part of his life – but are recipes for disaster in severe weather. Studies show that a typical mobile home can only withstand anywhere from 1/3 to sometimes as low as 1/5th the wind loads as a regular, site-built home of similar dimensions! Combine this with the fact that the density of housing in our region is several times higher than that of the sprawling, open plains, and the old notions, and the danger posed by even seemingly “regular” tornadoes (if you could even say there is such a thing) is exacerbated exponentially.

At the end of the day, all of this information exists for one main reason – to ensure that the relevant parties can warn as many people as possible, and are equipped with the right tools to do so. The National Weather Service and us in the Media do everything we can to ensure your safety, but when it comes down to the wire, the decisions YOU make are what will keep you and your family safe. Always be sure you and your loved ones know exactly what you all will do when a warning is issued – and be sure you have a reliable method of receiving them. One of the best places to be when tornado warnings are issued is underground, but this part of the country doesn’t have great topsoil for basements, so know where to go – ideally, a tornado shelter or certified safe room, or if unavailable, the lowest floor of your house, away from windows and doors, and away from outside walls. In an overwhelming majority of cases, this alone is enough to ensure your safety; so don’t hesitate. Stay tuned to Tennessee Valley Weather, and if a warning comes across… join us live and do what you need to do to stay safe. It’s not too difficult, and may just save your life.

1 thought on “Science Sunday: Is Tornado Alley Shifting East?”

  1. Bobby Hollingsworth

    Excellent article Bryan Chase Wilson.

    You always provide clear and concise information. And you have the heart of a lion when it comes to your interest in keeping the public informed and safe.

    We need more like you. And I’m sure there are many out there who will strive to follow in your footsteps.

    God bless you for your love of God, People, and Country!!!

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