#Growing Figs in Central Oklahoma

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"Growing Figs in Central Oklahoma" from OklahomaGardening

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Dixie Alley: The New Tornado Alley

Here is a paper I wrote back in May of 2016 about tornadoes and their trends based on location over the past decades. The main goal of this paper is to explain why we need to move on from the term “Tornado Alley”, as well as start constructing better homes in the Southeastern US.

Dixie Alley: The New Tornado Alley

 The area stretching from North Texas to South Dakota has commonly been referred to as “Tornado Alley.” Although the Great Plains do have a tornado season from mid-March to the end of May in which more tornadoes spin up than anywhere else on Earth, Dixie Alley has more tornado related fatalities in nine of eleven months out of the year, largely due to the population density. May and June the only months where the Plains Tornado Alley has more fatalities than Dixie, with July being the least active month for both areas. The winter months are a concern for the Southeast unlike the Great Plains. Moisture off the Gulf of Mexico can combat cold fronts out of the west, and if conditions are right, tornadoes can spawn. Warmer temperatures and higher dew points can create an unstable atmosphere ¾ of the year. The summer months are not as active because the horizontal temperature gradient is extended northward. While most buildings or residences in the Great Plains have basements or storm shelters, much of the Southeast is vulnerable because a lot of buildings do not have nearby shelters or basements. The objective of this paper is to explain why the Southeast needs a better preparedness system for future storms to come.

To make an argument about which tornado alley is the true tornado alley is wrong. Both areas produce many tornadoes every year, however Dixie Tornado Alley (DTA) is believed to be the most dangerous area to live in because of tornadoes. The Plains Tornado Alley (PTA) is significant because of its very active spring season. When comparing the two, many methods are gathered by using recorded data.

           The National Oceanic and Atmospheric Administration (NOAA) provides data dating back to 1800’s, but proper tornado recordings didn’t appear until the 1950’s. NOAA created the Storm Prediction Center, which has provided organized data that has benefited numerous weather-related research teams. The database provides physical attributes of tornadoes, for instance the Fujita damage scale, the width, the path length, and its’ location, as well as tornado related injuries or fatalities.

           To obtain specific comparisons between the two alleys, the alleys needed to be separated by location. Nebraska, Kansas, Oklahoma, and Texas all fall in the PTA, while Arkansas, Louisiana, Tennessee, Mississippi, Alabama, and Georgia comprise the DTA. It’s important to note that the PTA has larger total area than the DTA, but the DTA has 7,000,000 more people than the PTA. Then the overall number of tornadoes by each alley can be obtained and compared between the two. F2/EF2 or higher rated tornadoes are considered violent tornadoes. Mississippi has the most counties that have seen at least eight or more tornadoes rated F3 to F5 per 1,000 square miles from 1880 to 2003, which is nearly 3000 more square miles than state with the 2nd most, Oklahoma (Broyles, 3).  When first reviewing the data, there were substantially more tornadoes (3000+) in PTA compared to DTA, but there was an average of only 400 more ‘violent’ tornadoes in the PTA. Since there is so much data on numerous tornadoes, and most of them are EF1 or lower, the EF2 or higher tornadoes will be compared due to the significance of the rating, because they do substantial damage. Many comparisons can be made, like comparing the alleys based on the average number of violent tornadoes by month. The frequency of tornadoes can be obtained by number of tornadoes per a certain number of square miles. Most tornadoes occur in the afternoon or evening, and time of day can be compared between the two alleys. More nighttime violent tornadoes could mean more injuries or fatalities, because a lot of people would be asleep. The DTA has technically two tornado seasons, one in late fall through early winter, and the other in the late spring, but the PTA has a very active spring, so it will be interesting to see how things change throughout a typical year. Another comparison to make is on the number of tornado related injuries or deaths. An issue with this is the population density of the DTA. To properly make comparisons, a sample size will need to be used.

           Research on tornadoes dates back to 1950 when records began. The Dixie Tornado Alley (DTA) and the Plains Tornado Alley (PTA) are the main areas in the United States where the most tornadoes occur. More tornadoes occur in the PTA every year, mainly due to the peak season of May being the perfect time for tornadoes to spawn across the Central US. However, 80% of tornadoes that occur are EF0 or EF1. EF2 tornadoes and higher are less common, but are more significant due to the amount of damage they can produce. EF2 is defined by having 111-135 mph winds, meaning significant or considerable damage. Weather teams including the National Weather Service survey the damage done by a tornado the day after the event. Since wind speeds cannot currently measure wind speeds, the NWS assess the damage and comes up with a conclusion based on structural signs, trees, and power lines. An EF2 rating is determined when roofs are ripped off their homes, some exterior walls may have collapsed, vehicles can be lifted off the ground, mobile homes being totally destroyed, or tress snapping or up-rooted. Anything worse than this would be considered higher on the Enhanced Fujita scale. For this research, EF2 or higher will be considered as strong or violent tornadoes, and therefore this will be the focus of the research. The Fujita scale changed in 1973 to the Enhanced Fujita scale. They did this because often times, ratings were recorded higher than they should have been, so they implemented a guideline the NWS follows when going out to survey the damage the next day. Figure 1 highlights this change in the graphic below. After 1973, the number of significant tornadoes decreased as expected, at a rate of 1.5 per year (Schaefer). The overall reported tornadoes in the US have been increasing each year ever since recordings began. This is because population was less dense, so a lot of tornadoes went unnoticed. On average, 15 more tornadoes occur each year compared to the previous year (Schaefer). With the development of radar technology, meteorologists can notice where the tornado signatures like a “hook echo” or a strong coupling of changing winds. Survey teams can then pinpoint exactly where all the tornadoes tracked. Storm spotter networks have continuously expanded since the 1990’s (McCarthy). Figure 2 is a breakdown of Figure 1 based on location. The Great Plains has had a large drop in significant tornadoes since 1972. The Southeast has had fewer significant tornadoes since 1972, but the average has not decreased that much. There are more peaks in the Southeast, indicating the DTA has more significant tornado outbreak years than the PTA.

 (Fig. 1): a) Overall trend of reported tornadoes since 1950, b) Significant tornadoes by year

(Fig. 2): a) and b) show EF0 and EF1 rated tornadoes for the Great Plains and Southeast respectively; c) and d) show EF2 or higher rated tornadoes for the same areas.

             Using data from NOAA’s Storm Events Database, all tornadoes can be assessed and the information can be gathered easily based on the state. Adding up the number of EF2 tornadoes in Alabama, Tennessee, Mississippi, Arkansas, Georgia, and Louisiana, 916 strong tornadoes have occurred in the DTA, from the years 2000-2015. In the PTA, Nebraska, Kansas, Oklahoma, and Texas have accounted for 542 strong tornadoes for the same time period (NCDC). This is interesting because the PTA usually has more tornadoes annually, but this includes EF0 or EF1 ratings. The PTA spans roughly more than 400,000 square miles, compared to DTA’s 275,000 square miles. However, data gathered from the government’s census page shows that 32,270,000 people live in DTA and 35,700,000 live in PTA. This is pretty close, even with though Texas accounts for 27,000,000 of the 35,700,000 people. Obviously, the population density is much higher in the DTA. Rural areas make up most of the Central Plains, while suburbs and growing cities are more common in the Southeast. From this we can expect more deaths to occur in the DTA due to more strong/violent tornadoes and a higher population density. DTA had 627 fatalities from tornadoes over the past 15 years, while the PTA has had just 150 (NCDC). This is determined by adding up all the fatalities by state from NOAA’s Storm Events Database.

           Overall frequency of tornadoes is much higher in the PTA with roughly 13,500 tornadoes reported since 1950. The DTA has had around 7,500 since records began. By averaging the number of strong tornadoes annually based on month, we can determine when these violent tornadoes will likely occur. The PTA has only one tornado season and it lasts only a few months (April-June), nearly 76% of strong tornadoes occur in this time frame (Gerard, 148). The DTA however has recorded many strong tornadoes occurring between November and May, and only 40% of these tornadoes occur in the spring months. The time of day is very important as well. Overnight tornadoes are less common, but are very important because most people are asleep. By using the data, we can determine the frequency of when strong tornadoes occur. Since NOAA’s page has everything from population, to tornado width and length, to duration, and much more, many comparisons can be made. Most tornadoes occur in the late afternoon to evening hours, but the DTA has a 50% greater risk for overnight strong tornadoes than the PTA (Gerard, 154). The PTA has a shorter time frame for tornadoes, 3pm -8pm. Roughly 1/3 of deaths by tornadoes in the DTA occur at night, compared to 1/5 in PTA (Gerard, 153).

Topography is much different between the two areas. The Southeast has more hills and trees, making it difficult to see an oncoming tornado. This and many other factors likely increase the number of fatalities seen in the DTA.  Alabama has had more strong tornadoes than Texas over the past 15 years, but Texas has had substantially more since 1985. April 27, 2011 was a major severe weather outbreak day across the Southeast; this abnormal event can skew average data. An event like this occurs roughly every 25 years. NOAA’s page has many variables that can be assessed. Other variables can then be compared like damage costs to rebuild or even comparing the duration of strong tornadoes between the alleys. Figure 3 shows the average annual number of significant tornadoes passing within 25 miles of a point between 1973 and 2010 (Dixon). The graphic changed drastically after 2011 due to the outbreak in late April, as seen in Figure 4.

Fig. 3) Average annual number of significant tornadoes from 1972 to 2010

Fig. 4) Average annual number of significant tornadoes from 1972-2011

Fig. 5) Average annual number of tornadoes with a path length >10 miles from 1972-2010

The pathlength of a tornado is also important. The longer they stay on the ground, the more destructive they can be. Figure 5 highlights where the longest-lived tornadoes typically occur. Central Mississippi up to Northern Alabama could see nine long-tracked tornadoes every year.

The data and comparisons have been made between the Dixie Tornado Alley and the Plains Tornado Alley. The PTA has been known to be the true tornado alley in the past, but with this research it has come apparent that the DTA is the most dangerous area when it comes to tornadoes. Although the PTA has the most tornadoes annually, most of these tornadoes are weaker tornadoes (EF0, EF1), and their tornado season only spans a few months in the spring. The DTA has technically two tornado seasons: September to December and February to May. This is because of how the systems set up during the spring and fall months. The DTA experiences tornadoes in the fall because the Gulf of Mexico is warmer than in the springtime because water takes longer to warm up and cool down. After the summer months, the water is warmer; therefore higher dew points seep into the Southeastern states. High dew points, or a high relative humidity is a major ingredient in the formation of tornadoes. Tornadoes also need lift, or convergence of winds at the surface, instability in the atmosphere, a large angle between surface winds and winds aloft, and a high CAPE, or convective area of potential energy. In the springtime, a dry line sets up in the Plains, and when a low-pressure system moves through the area, sever weather breaks out. The PTA in May has the most tornadoes out of any month in both locations. Since the PTA does not have source of moisture as well as the DTA does with the Gulf, the PTA relies on daytime heating to create instability in the atmosphere. When the Sun heats the ground, latent heat is release, which adds water vapor and instability in the atmosphere. Overnight this boundary level lowers and cools due to the lack of sunlight causing warmth in the air. As a result, the PTA sees substantially less overnight tornadoes than the DTA does. The DTA still has access to the abundant moisture off the Gulf of Mexico at night. Therefore, the DTA has a 50% greater risk of strong tornadoes during the overnight hours than the PTA. Although more tornadoes occur in the PTA annually, the DTA has more strong/ violent tornadoes annually. The PTA has a high-risk peak season compared to a more moderate risk longer season the DTA has. Over the pass 30 years, 75% of tornado fatalities in the US have occurred in the DTA. The population density of the DTA is much higher than the PTA, so there’s a higher chance for a tornado to hit a building in the Southeast than in the Plains. The PTA is very rural, and a lot of the tornadoes that touch down go unreported because no one sees them. Even if there is a tornado signature on Doppler radar, a tornado may go unrecorded, which could skew research. In the PTA, topography is flat, so people can see the storm coming from a few miles away. In the DTA however, there are more hills, valleys, and trees, and a lot of tornadoes “sneak” up on people who cannot see them. In conclusion, the DTA is more dangerous than the PTA for all the reasons stated. There’s a longer season for a chance of a tornado outbreak, but the PTA does have more tornadoes, even if most of them are weaker ones. Both areas have the most tornadoes in the world, so they are both dangerous areas to live in. The PTA has been known to have more shelters than the DTA. Most houses built in the Plains have basements or storms shelters, unlike the Southeast. Perhaps in the past when they built the houses, it was less common to see dangerous tornadoes in the Southeast and more in the Plains.

Today the Southeast faces a greater risk of a tornado threat than in the Great Plains. The Southeast needs to better construct homes to have a shelter, or communities should just build more storm shelters. Mainly, people in the Southeast need to be aware of the risks of living in the DTA. Apathy has been a concern for the Southeast in the past, but after April 27, 2011, a lot people recognized the importance of taking these tornadoes seriously. With the ever-increasing population, expansion of urban areas, and therefore the expansion of suburbs around the cities, chances of a tornado hitting a populated community can only increase. The assumption of tornadoes being more dangerous in the tornado alley (PTA) is no longer true. Although the most dangerous alley is the South, including Oklahoma and Texas, all the way to Georgia, and south of Kentucky to Northern Alabama.

 References:

·               Gerard, Alan, The National Weather Service: National Weather Digest, Jackson, MS. December 2010

http://www.nwas.org/digest/papers/2010/Vol34No2/Pg145-Gagan-etal.pdf

·               Dixon, P. Grady, Mississippi State University, Mississippi State, MS; Coleman, Timothy, University of Alabama Huntsville, An Objective Analysis of Tornado Risk in the United States. American Meteorological Society.

http://journals.ametsoc.org/doi/full/10.1175/WAF-D-13-00057.1

(Where all the figure came from)

·               McCarthy, D. W., and J. T. Schaefer, 2004: Tornado trends over the past 30 years, 14th Conference of Applied Climatology, Seattle, WA, American Meteorological Society, 3.4

https://ams.confex.com/ams/84Annual/techprogram/paper_72089.htm

·               Dolce, Chris, The Weather Channel, March 2015: How Many Tornadoes Has Your City Seen Since 1950?

https://weather.com/storms/tornado/news/tornadoes-by-month-cities

·               Schaefer, Joseph T., Norman, OK: The SPC Tornado/Severe Thunderstorm Database

https://ams.confex.com/ams/99annual/abstracts/1360.htm

·               Broyles, Chris and Crosbie, Casey, Storm Prediction Center, 2004: Evidence of Smaller Tornado Alleys Across the United States Based on Long Track F3 to F5 Tornado Climatology Study from 1880 to 2003.

http://www.spc.noaa.gov/publications/broyles/longtrak.pdf

·               https://www.census.gov/popest/data/maps/2011/PopDensity_11.pdf

·               http://www.esrl.noaa.gov/psd/data/

·               http://www.ncdc.noaa.gov/stormevents/

·               http://w2.weather.gov/climate/index.php?wfo=lsx

If you have any questions or concerns, please comment below!

Thanks for reading!

Merritt Turner