Monday, February 18, 2013

11 Reasons why Mid-South tornadoes are so insidious

While Tornado Alley may be the Hollywood backdrop for storm-chasing worthy tornado action, those of us living in the south know that Tornado Alley's redneck cousin, Dixie Alley, is where the real action is when it comes to deadly tornadoes!  In fact, statistics show that Dixie Alley is where the majority of killer events occur.  

The graphics below show that, while the frequency of tornadoes is highest across the Plains from the Corn Belt to north Texas, killer tornadoes are most likely in the Mid-South and Tennessee Valley.  In fact, the highest frequency of significant (EF-2+) tornadoes stretches from a peak in the Red River Valley east into the mid-lower Mississippi Valley, including the Mid-South.


In light of the statistics above, here are 11 reasons why Dixie Alley tornadoes, as compared to those in Tornado Alley, are more insidious (in no particular order).

1. High frequency overall - While Tornado Alley boasts the greatest number of overall tornadoes in the nation, and perhaps the world, the south is no slouch. And in fact, when considering "significant tornadoes" (EF-2+), Dixie Alley and the Mid-South in particular are just behind Oklahoma and the Red River Valley and exceed most of the Plain states. The average annual number of tornadoes in Dixie Alley per 10,000 square miles is 6-9+, rivaling just about any other area in the nation.


2. Frequency of nocturnal tornadoes - Just about anyone living in Dixie Alley for any length of time can tell you that the sound of tornado sirens wailing or Weather Radios screeching in the middle of the night is enough to either frighten or frustrate nearly everyone, especially when it occurs on a relatively frequent basis. In fact, AR, TN, MS, and AL all have 50% or more of their tornado deaths at night, with TN at 73.3%! Due to the likelihood of more tornadoes in transitions seasons (more in #3 below) than other areas, more tornadoes also occur after dark. When is the most likely time to die in a tornado?  When you can't see it coming or are sleeping through a warning (at least until it's too late).


3. No well-defined tornado season - Alluded to above, unlike Tornado Alley when tornadoes are generally concentrated during "tornado season" from roughly April-June, Dixie Alley sees an abundance of tornadic storms in the "cool" or transitions seasons.  In fact, there is a notable severe weather peak (albeit lower than spring time) in November and early December in the South that exists nowhere else in the U.S. However, it is not unusual (despite post-storm media reports to the contrary) to see tornadoes in winter and even summer (one of the best "off-season" examples being the Super Tuesday Outbreak of February 2008).  When tornado season is spread out over the course of the year, preparedness and awareness tend to be low.  In Tornado Alley, the preparedness level in the spring is at an all-time high.

Comparison of strong & violent tornadoes by month for Tornado Alley (red) and Dixie Alley (green). Gagan  et al, 2010.

4. Fast storm motion - Because of the nature of Dixie Alley storms to occur more often in the spring and fall, the storms that develop tend to be pushed by a stronger jet stream than in the late spring/summer when jet streams are typically less vivacious. A stronger jet results in faster moving storms. Faster moving storms mean A) less time for forecasters to react and warn the public (though southern meteorologists take this into account and by and large do a fantastic job at providing excellent lead time) and B) less time for the public to process the threat and respond accordingly. When a tornado is moving at 40-50+ mph, it doesn't take long to cross the typical county and residents must be ready to take cover when the warning is issued. Some of the videos of Dixie Alley tornadoes appear to be time-lapsed when in reality the funnels really are moving THAT fast!

5.  Rain-wrapped funnels - This refers to the nature of southern tornadoes to tend to be less "visible" to the public due to having rain surrounding the funnel.  In Tornado Alley, moisture is often not nearly as abundant as in the South, where southerly wind off the generous Gulf of Mexico provides ample moisture for heavy rainfall.  In addition, higher low level humidity also means lower cloud bases.  These factors result in tornadoes in the Plains that are "picturesque," with their funnels easily identifiable from a long distance, while in Dixie Alley, what appears to be a heavy shower could actually be masking a deadly swirl of air lurking inside. 

Where's the tornado?  (Hint: where the transformer is blowing.) Photo credit: Dr. William T. Hark.
6. Terrain / trees - The South loves it's trees. They're everywhere and they make for great scenery, ample lumber, and cool shade in unbearably hot and humid summers.  Hilly terrain (at least moreso than the Plains - outside of the Mississippi Delta region) also provides for scenic Sunday drives and interesting local effects on the weather.  However, vegetation and terrain also make for a great game of hide-and-seek with tornadoes.  Visibility, as in #5, significantly affects the ability to survive a twister.

Nearby tornado hidden by trees, Photo credit in image.
7.  High population density - While it may seem that there are lots of rural areas in the South, when compared to the miles upon miles of deserted farm and pasture land of the Plains, the population density of Dixie Alley is actually much higher than in Tornado Alley.  If a tornado touches down in the middle of nowhere in Kansas and no chasers are there to record it, does it even count?  Try doing that in the South.  If it's not brushing up against a mid-size or larger city, there are likely at least 2-3 hamlets or single-stoplight towns in the path. Bottom line: nearly every tornado in Dixie Alley will affect SOMEBODY.

8. Low quality construction - Hate to say it, but it's a fact. Housing stock in the southeast U.S. is, on average, poorer than the Plains.  In particular, the abundance of mobile homes, manufactured homes, or trailers (or whatever you want to call them), means that even the weakest tornadoes can wreak havoc on the occupants of one of these dwellings. Here are the facts: from 2001-2005,  nearly 57% of all tornado fatalities occurred in non-permanent housing and the number has consistently been rising. Stick-built, or permanent, houses accounted for just over 25% of tornado deaths. In AR, AL, GA, MS, and TN from 1985-2005, 52% of all tornado deaths occurred in mobile homes. Add to that that the southeast U.S. has the highest percentage of mobile homes east of the Rockies and you have a recipe for disaster. More mobile homes = more death.

Mobile home park after a tornado. Photo credit: http://thetornadoallie.blogspot.com.
9. Lack of basements and storm shelters - Anecdotally, we know that there are very few underground places of shelter in the southeast.  Due primarily to construction costs among other factors, basements are very rare.  In addition, storm shelters are also rare, likely due to their relatively high cost as compared to demographics.  In Tornado Alley, a large percentage of the population has either a basement or a storm shelter. Some tornadoes are only survivable if you are underground, plain and simple.  Even the most well-constructed homes are Lincoln Logs to an EF-4/5. 

Germantown, TN tornado, originally posted on the MWN Blog. Photo credit: Edgar Babian.
10. Demographics - It is what it is.  The "social vulnerability" of those living in Dixie Alley is higher than in other tornado-prone areas of the country. Poverty is higher (which likely factors into #8 above) and the age of the populace is higher.  Both likely contribute to the fatality rate. In fact, the percentage of tornado fatalities of those over age 50 is higher than the percent of the population of that age, suggesting that older people are more vulnerable.  On the other hand, the percentage of tornado deaths of those under 30 is much lower than the percentage of the population in those age brackets, meaning younger people tend to do a better job of heeding the storms and sheltering appropriately.

Percentage of tornado fatalities vs general population by age.  Ashley 2007.

11. Apathy - Perhaps the hardest, and easiest, reason to understand, there's no getting the fact that we tend to be apathetic. "It'll never happen to me." "The sirens are always sounding." "Tornadoes don't happen at this time of year/day."  Helen Keller said, "Science may have found a cure for most evils; but it has found no remedy for the worst of them all - the apathy of human beings."  True, the false alarm rate for tornado warnings is high - but which would you rather have, a few extra warnings or one that truly does his "without warning?"  The science is improving and false alarms are decreasing, but we have to counter apathy with education and information.

The bottom line

Mississippi, Alabama, and Tennessee lead the nation in terms of tornado deaths per square kilometer AND killer tornadoes per square kilometer. Most of the other states in Dixie Alley also have averages well above the rest of the nation. While we don't see as many tornadoes by sheer number, Dixie Alley is the most vulnerable part of the nation when it comes to severe weather, due to all of the factors described above.  Most of these factors won't change, but an apathetic populace is inexcusable. The National Weather Service offices across the south know exactly what they are dealing with and do a fantastic job warning the public when severe weather is possible, sometimes days in advance.

Every home must have a NOAA Weather Radio programmed for the county in which it resides. We need to stop relying on outdoor sirens to be the sole warning of impending storms. Technology now allows us to reduce apathy by targeting warnings to those in the path of the storm. Our mission at MemphisWeather.net and Cirrus Weather Solutions is to do whatever we can to get the body count down and the awareness up. Whether you use our services, or someone else's makes no difference to us. But the information is there. It's time to put on your big boy/girl pants and make sure that you survive the next tornado!

References:

Ashley, W., 2007: Spatial and Temporal Analysis of Tornado Fatalities in the United States: 1880-2005. Weather & Forecasting, 22, 1214-1228. Available online at http://journals.ametsoc.org/doi/pdf/10.1175/2007WAF2007004.1

Gagan, John, et al, 2010: A Historical and Statistical Comparison of "Tornado Alley" to "Dixie Alley." National Weather Digest, 34, 145-155. Available online at http://www.nwas.org/digest/papers/2010/Vol34No2/Pg145-Gagan-etal.pdf

Husted, R., 2012: Mid-South Severe Weather Climatology. Available online at http://www.srh.noaa.gov/images/meg/Mid-SouthSevereClimatologyStudySummary2012.pdf

National Climatic Data Center, 2012: U.S. Tornado Climatology. Available online at http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html

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7 comments:

DanTheCigarMan said...

Excellent Information!

Chuck Doswell said...

The notion that a high water table prohibits construction of basements is a total myth! The builders like to build homes quickly and it takes more time to add a basement.

MWN/Erik said...

Thanks for your comment, Mr. Doswell. I have actually just learned that recently - you are correct. Cost and pace of construction have a great deal to do with it, much moreso than water table. I had neglected to go back and correct this and will do so now.

Thanks for taking the time to read and comment! Always enjoy reading your work and listening to what you have to say. I heard you speak at the MS State Severe Weather Symposium a couple of years ago and thoroughly enjoyed it, while learning a great deal as well!

--Erik, Meteorologist, MemphisWeather.net

Anonymous said...

So all those times I thought I went through a tornado (sound, odd air change just before the winds go crazy, extreme storms, extreme damage) I probably did go through one. I've always written things off as 'well it sounded like one and there was a warning or watch but I didn't see a funnel so it must've just been a really powerful storm.' It is a scary realization to know I was writing off storms/tornadoes that way. Everything you've mentioned from the crazy night time storms that sometimes rip through quickly and cause major damage to the rain cover and tree cover makes perfect sense. I hope more people in TN and the South take note. We've been writing off things as just 'big storms' and putting ourselves at risk.

Hima Dev said...

Most of the tornadoes that have happened recently has been highly destructive especially the nocturnal ones. They give immense destruction to life and buildings.

Anonymous said...

It's a shame that in-ground shelters are so expensive. I'm sure they would sell a lot of them if they were more affordable but as it is, they probably sell very few of them. I know no one that has been able to afford one.

MWN/Erik said...

We are closely affiliated with one such shelter company, Take Cover Storm Shelters, and theirs are about as inexpensive as you can find given the cost of materials and labor. It is no small task to assemble the steel into an approved shelter and then spend a day installing, including use of heavy equipment. For about $4000, it's a good investment in peace of mind. They actually stay very busy in the Memphis/Mid-South area. They are not cheap, but they are within the range of affordability for many people.

--Erik