Effects of Above Average Temperatures on Tornado Intensity and Frequency
By: Nicholas Colona
Thesis
Carthage College
Department of Geography and Earth Science
Adviser: Dr. Matt Zorn
April 15, 2011
Abstract
The heart of America is best known for its tornadoes, that is why it is called tornado
alley. Previous research has been done about global warming and how possibly the warming of
the earth’s overall temperature could have an effect on our storms, specifically tornadoes.
Twenty five states in the central United States over a 60 year period from 1950 to 2009 were
studied. The factors that were studied were whether when the temperatures were above normal
temperatures, the intensity and frequency of F3 or higher tornadoes would be greater than if the
temperature was normal or below normal. The data was analyzed both statistically and spatially.
When the temperatures were not normal it was found that there were some statistically higher
chances for F3 or higher tornadoes to occur. Also looking at the different aspect of what makes
up a tornado it was found that indeed when the temperature were not normal there was a better
chance that tornadoes would be more intense. It was also determined that tornadoes do seem to
mainly cluster in the tornado alley region in the central United States, with small clusters
scattered around the surrounding areas. In future studies it was recommended to simply keep the
study going as global warming continues to be an issue, and possibly shrink the study area to
look at the heart of tornado alley and to compare more aspects of tornadoes as we become more
knowledgeable about how they form and react.
2
Table of Contents
Page #
List of Figures
4
List of Tables
5
Introduction
6
Methods
13
Data Acquisition
13
Spatial Analysis
14
GIS Analysis
14
Results
15
Discussion
26
Conclusion
30
Recommendations
31
Acknowledgements
32
References
33
3
List of Figures
1. Study Area
13
2. Above Normal Temperatures
16
3. Normal Temperatures
16
4. Below Normal Temperatures
17
5. Above Normal Tornado Tracks
18
6. Normal Tornado Tracks
18
7. Below Normal Tornado Tracks
19
8. Above Normal Mean Center
22
9. Normal Mean Center
22
10. Below Normal Mean Center
23
11. Above Normal Density
24
12. Normal Density
24
13. Below Normal Density
25
4
List of Tables
1. The years for the three temperature groups
15
2. Average Number of Tornadoes Per Year
15
3. All three temperature groups with F3 and higher averages and percent
19
4. Above Normal Temp Tornadoes
20
5. Normal Temp Tornadoes
21
6. Below Normal Temp Tornadoes
21
5
I. Introduction
Temperature is just one of the many aspects that affects how and why a tornado develops.
This thesis takes a look at the effects that temperature has on tornadoes, and more specifically
their intensity and frequency. I hypothesize that the warmer the temperature is, the more intense
the tornadoes will become, and the frequency at which these tornadoes occur will be greater as
well.
One of the most terrifying and well known natural disasters is the tornado. Even though it is
well known, especially if you live in what is known as “tornado alley”, you will probably never
see a tornado in your life (Douglas 2005). Tornado alley consists of much of the entire central
United States. It mainly consists of Oklahoma, Kansa, Nebraska, Missouri, Arkansas, the panhandle of Texas, and the tip of Louisiana (Douglas 2005). But what is a tornado and how is it
formed? A tornado by definition is a narrow funnel of intense wind that typically has a rapid
counterclockwise rotation and is in contact with the ground (Hyndman 2009). They usually form
underneath a cumulonimbus cloud or a thunderstorm.
How a tornado is formed is actually a very lengthy process. Tornadoes derive their energy
from the latent heat that is released with water vapor in the atmosphere and condenses to form
raindrops (Hyndman 2009). When cold polar air meets with warm tropical air it creates a great
instability in the air, resulting in the formation of a supercell. The great instability is caused by
the warm air rising over the more dense colder air. A squall line, or narrow zone of
cumulonimbus clouds forms, which will also create a wall cloud from which the tornado will
eventually come. The wall cloud will usually form on the southwestern part of the storm due to
6
the fact that this is where the warm moist air is blowing into the storm from the updraft. This
wall cloud will then start to rotate due to the updraft and the wind shear that comes from the
instability of the air. Soon after, the easiest recognizable part of the tornado, the funnel, will start
to descend from the base of the cloud. In actuality, it does not descend, but rather the pressure
within the cloud drops due to the increasing wind speeds. This is known as Bernoulli's principle.
As the pressure drops, it causes moisture in the air to condense. This action continues down the
spiral, giving the impression that the funnel is descending from the cloud base. The tornado is
not actually made up of cloud, but rather just dust and debris that gets picked up from the intense
high winds swirling around on the ground. The result is a tornado (Williams 2009).
Tornadoes are one of the most deadly forces in the world. They can strike at any time and
there is much that is still unknown about these natural killers. However, someone had to come up
with a way to rate them. That man was Ted Fujita, and he came up with the Fujita scale for rating
tornadoes. Tornadoes are rated according to four different criteria: their wind speed, the width of
the tornado, the length of the path, and the damage that was caused by the tornado (Douglas
2005). There are currently six ratings in the Fujita scale: F0 to F5. For the purpose of this thesis,
I am going to be looking at intense tornadoes with which I am going to classify as F3 or higher.
An F3 tornado has winds of 158 to 206 mph, it has to be between 176 to 556 yards wide, and it
has to last at least 10 to 30 miles as well as cause severe damage to the affected area. An F4
tornado has to have winds of 207 to 260 mph, it has to be between .34 to .9 miles wide, and has
to last for at least 32 to 99 miles causing devastating damage to the affected area. Finally, an F5
tornado has to have winds of 261 to 318 mph, it has to be 1 to 3 miles wide, and it has to last at
least 100 to 315 miles causing incredible amount of damage to the area affected, usually these
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tornadoes will take out an entire town if it passes through one. Also to note, there is an F6 scale
but there technically has never been an F6 tornado recorded. The winds would have to be greater
than 319 mph and the width and length is currently unknown as well as the damage it would
cause would be beyond our comprehension (Douglas 2005). Then you have the enhanced Fujita
scale. The only difference it has from the original scale is that the wind speeds for each F0 to F5
are greater, with F3 ending at 267, F4 at 318, and F5 at 374 mph. The width, the length, and the
damage assessments are the same for each level (Hyndman 2009). Along with the Fujita scale,
which includes length, width, and damage, I am going to be comparing the number of injuries or
deaths and the location of each tornado that I look at in my study.
Just like with most things, tornadoes do have a season in which they are most likely to occur
in. In the United States, the tornado season is generally in the spring, with tornadoes being more
prevalent from April through July, with May and June being the peak months, yet tornadoes can
form any time of the year (Williams 2009). For my thesis I am going to be looking at the months
March through September so I can get a wider range of tornadoes and temperature data. I also
chose this so I could have seven months, because with seven months there would be a better
average for the temperature. As with a longer period, it will give me more of an average
temperature for the season.
One of the reasons I am doing this study is because of the idea of Global Warming that is
currently making its way through the scientific community. There are some researchers that say
global warming is upon us, and then there are of course others that just say global warming is a
just a natural trend that the planet goes through and will eventually correct itself. Nonetheless it
is a pretty well-known fact that the average temperature of the earth, as a whole, has increased by
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almost an entire degree over the past years. What is global warming? Well it is a rather simple
process. In short, radiation from the sun comes into the atmosphere and it is either absorbed or
reflected. The absorbed radiation will eventually be reradiated out from the earth’s surface back
into the atmosphere, and some of this leaves and goes out into space. This is where global
warming starts to come into effect. Greenhouse gases are naturally in the atmosphere, carbon
dioxide being one of the major gases. Recently the world has been releasing tons and tons of this
gas into the atmosphere changing the composition of the upper atmosphere. Now these
greenhouse gases are what keep the earth at its stable temperature, trapping some of this
radiation in as heat, but if we add more greenhouse gases to the air, then these gases are going to
trap more radiation in the earth’s atmosphere, thereby making the earth warmer, and this is
basically what global warming is (Christopherson 2006). The IPCC is forecasting for the
temperatures in the 21st century to rise by about 5.6 degrees F, with the highest possible being
10.4 degrees F and lowest being 2.5 degrees F (Christopherson 2006). There are going to be
many consequences of global warming. It will affect the world food supply which will in turn
affect the economy which will in turn have a snowball effect and it will just keep leading to more
and more things. Another major affect it is going to have is very well known, it is going to
impact the rise of sea levels around the world. And this could have devastating consequences for
the world, as a majority of the world’s population lives near a coastal area. Major cities would be
flooded and a lot of land would be lost, which would make other cities more crowded and again
it would just have a snowball effect and just continue to cause problems. And the last fear that
many people have is that this warming temperatures are going to lead to more intense storms, all
over the planet (Christopherson 2006).
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If the average temperatures are rising for the earth, then I believe that this will have an effect
on tornado activity. Because I believe that warmer than normal temperatures will in fact make
tornadoes more intense and more frequent, and perhaps one day we might actually get an F6
tornado to touch down somewhere. There was a study done by the University of Stanford in
2008 on this exact topic, “Does Global Warming Influence Tornado Activity”. One thing they
found was that severe thunderstorms that spawn tornadoes arise in a larger-scale environment
characterized by large vertical wind shear and convective available potential energy (CAPE),
among other conditions and in general, global warming is expected to increase CAPE by
increasing temperature and humidity within the atmospheric boundary layer (Diffenbaugh et al.
2008). So with this we will maybe see a rise in tornado activity or intensity in the future as global
warming continues. They also found that along with the CAPE increase, the wind shear could
possibly decrease, or just perhaps move northward. And with this many things could occur;
temperatures could become colder and therefore push back the tornado season a bit, or it could
possibly move where the tornadoes occur, most likely to the north, but it’s all really unknown
right now just because this is all predictions of what might happen (Diffenbaugh et. al. 2008).
And they go on to say that currently right now it is very difficult to say whether or not global
warming will have any effect on tornado activity in the future. There is simple too much that is
not known right now about tornadoes and how they form to get an accurate prediction in future
models. They are very hard to put into a long term climate model because of this, because long
term climate models tend to be very simple, with few aspects in them, and tornadoes are too
complex to put into that model (Diffenbaugh et. al. 2008). So all in all, global warming will have
some effect on tornadoes in the future, this is for sure known, but what that effect will be, I hope
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to show that it will increase frequency and intensity of tornadoes, but right now based off models
and predictions, it is largely unknown.
My study area for this thesis is going to be all of central United States. I choose this for a
couple of reason, one is that this is where the most tornadoes in the world occur, we live in the
perfect place for tornadoes to happen, and I chose to expand it outside of just tornado alley so
hopefully we can see a better trend in the results and more data would be able to be used. I
examined a study done by NOAA and the National Climatic Data Center and they looked at
global warming in the United States. This study was done in 1995 which is quite a ways back but
what they wanted to achieve was to set a model that could predict future climates. They came up
with the Climate Extremes Index and the Greenhouse Climate Response Index (Karl et. al.
1995). These models started off very basic and since they came out they have continued to add
other indices into them to make them more reliable. Over the past five decades or so
temperatures have been on the rise in the United States, and most believe that this is closely
related to global warming. So global warming is happening in the United States and I hope to
show this in my study.
Tornadoes are a very powerful force of nature. They can occur anywhere and anytime, as
long as conditions are favorable for them. I think one of the reasons these storms are still so
deadly is just by the fact that there is still so much we do not know about them. Like on May 4,
2007, there was an F5 tornado that touched down in Greensburg Kansas. The national weather
service was able to provide a 50 minute tornado warning to the area that was affected and also
they were able to give a 10-15 minute warning with tornado sirens after they predicted is precise
path it would take. Despite all of these efforts, nine people still sadly were killed, and the entire
11
town was destroyed in minutes. Only 1600 people lived in this town but still the damage totals
reached 153 million dollars (Hydnman2009). It is hard to imagine what would have happened if
this tornado would of hit a more populated area, the damages and death toll would have been
extremely higher. And I know that my study will not do anything to help prevent the destruction
that tornadoes like this will cause, but instead the reason I am doing this study is because I wish
to be able to show a trend that when temperatures are above average, there is a greater chance
that more intense deadly tornadoes like the May 4th tornado will strike. And in turn if we can
show that the temperature is in fact warming as a whole and that if we can establish exactly what
effects global warming will have on tornadoes we can make the research into tornadoes more
main stream, and start looking into finding materials that we can use to build buildings and
houses to help saves lives and help give some people that live in tornado alley a since of comfort,
in that even if a tornado does indeed hit their house, they will not lose everything they have, and
their lives will be safe.
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II. Methods
Data Acquisition
My study for this thesis is going to be all of the Central United States. I choose this
because this is the best place in the world for tornadoes to occur, and there is a lot of data for this
region. All of my tornado data that I will be working with came from the National Weather
Service in Sullivan, WI (http://www.crh.noaa.gov/mkx/). I was in contact with them and I was
able to receive from them a CD with GIS plotted data of tornado tracks for every tornado that has
occurred in the United States starting in the year 1950. There are a number of different variables
that came on the CD. These include: the F-rating of the tornado, the length it was on the ground,
latitude/longitude of where the tornado took place, the width of each tornado, and the date and
time the tornado occurred. For this thesis I will also be using temperature data for the years 1950
to 2009, more specifically the months March to September during those years. I am getting this
data from the NOAA website. On their website they have a program that all I will have to do is
just plug in the area and time that I want to get data and it give me a graph that has each year on
it with the average temperature for the month I asked for and it also gives me the average
temperature for that month over the entire sixty year period. I plan on doing this for each month
and for each state that is in my study area and then just combining the same years together and
then getting an overall temperature for the sixty years and for each year as well.
Figure 1: Study Area Map
13
Statistical Analysis
First I am going to take the average of every month, March to September, for the years
1950 to 2009. And then I will be taking the standard deviation of this to get a set of three groups:
Above average, average, and below average. Each of these groups will represent different years
where the temperature was either warmer or colder or just average. Then I will just be comparing
all three of these groups against each other, and looking to see what the tornadoes were like
during the years that fall into the different groups. I plan on just basically comparing the F-scale
of each tornado, but also I will look at the other aspects that the tornado had such as damage or
injuries or any of the aspects I mentioned above.
GIS Analysis
I plan on mapping out my three different temperature groups, to show where it was colder
and where it was warmer over my study area. I am going to make maps also of the tornadoes that
occurred during my three different year periods. And with this I hope to show the trend that
when it is warmer that not only there more tornadoes, but the F-scale of those tornadoes are
statistically higher than in the average temperature years and below average temperature years. I
also plan on doing some spatial mapping of my study area and with the tornado tracks and
temperature data but I am going to wait until after I run the data and see where I can go with that.
14
III. Results
After finding all of the temperature averages for each state in my study area I found that
there was an overall average of 63.2oF with a standard deviation of 1. Then after adding and
subtracting 1 from the overall mean I had my limits for my three temperature groups; above
normal is from 64.2 and up, normal was from 62.3 to 64.1, and below normal was from 62.2 and
down. Going through each year and assigning a different group for each I found that during my
sixty year period I had 14 above normal years, 36 normal years, and 10 below normal years
(Table1).
Table 1: The years for the three temperature groups (AN-14, N-36, BN-10)
Above Normal Temperatures
Normal Temperatures
Below Normal Temperatures
1954, 1955, 1963, 1977, 1980, 1986,
1952, 1953, 1956, 1957, 1958, 1959,
1950, 1951, 1965, 1967, 1974, 1975,
1987, 1988, 1990, 1991, 1998, 2000,
1960, 1961, 1962, 1964, 1966, 1968,
1984, 1992, 1993, 1996
2005, 2007
1969, 1970, 1971, 1972, 1973, 1976,
1978, 1979, 1981, 1982, 1983, 1985,
1989, 1994, 1995, 1997, 1999, 2001,
2002, 2003, 2004, 2006, 2008, 2009
Table 1: Average Number of Tornadoes per Year
Above Normal Temps
14 Years
3066 Tornadoes
219 Tornadoes / Year
Normal Temps
36 Years
8326 Tornadoes
231.2 Tornadoes/Year
Below Normal Temps
10 Years
1783 Tornadoes
178.3 Tornadoes/Year
I then mapped out the three different years to show the spatial differences of the
temperatures in each group. I did this just to show what the temperature ranges were for each of
the three groups and also to give an idea of how the temperatures were throughout my study area.
Here are the three different maps starting with the above normal temperatures and I tried to make
the colors go along with what the map was representing, brighter colors for above normal and
colder colors for below normal temperatures.
15
Figure 2: Above Normal Temperatures
Figure 3: Normal Temperatures
16
Figure 4: Below Normal Temperatures
I then needed to find the tornado tracks for the three different groups for the area of my
study, using ArcMap I used the select by location and came up with the next three maps for
tornado tracks for each of the groups. In the above normal map there are a total of 3066 tracks,
for the normal map there are 8326 tracks, and finally for the below normal map there was 1783
tracks. And in these for the above normal group there is a total of 363 F3 tornadoes and higher,
for normal there were 1157 tornadoes, and for the below normal group there was 407 and F3 and
higher tornadoes.
17
Figure 5: Above Normal Tornado Tracks
Figure 6: Normal Tornado Tracks
18
Figure 7: Below Normal Tornado Tracks
I found that for these three periods, that the below normal temperature group was
statistically more likely to have an F3 or higher tornado occur, so tornadoes during the below
normal years F3 or higher occurred more frequently. As during these years an F5 had a .953% of
occurring, an F4 occurred 6.89% of the time, and an F3 occurred 14.97% of the time out of all
the tornadoes. Comparing these statistics to the other two years they were higher on all three F5,
F4 and F3 tornado occurrences (Table 2).
Table 2: All three temperature groups with F3 and higher averages and percent
F5
F4
F3
Length
Width
Injuries
Deaths
Above
Normal
Temps
Normal
Temps
.456%
2.48%
8.90%
20.06
Miles
531.1
Yards
14.83 1.42
$400+
People People Million
.396%
3.11%
Below
Normal
Temps
.953%
6.89%
10.34% 20.78
Miles
14.97% 21.4
Miles
435.16
Yards
398.2
Yards
25.16
People
37.69
People
1.75
People
2.34
Deaths
Damage
$40+
Million
$450+
Thousand
19
With (Table 2) you can see all of the averages for each category for each of the three
groups; with length, width, injuries, deaths, and amount of damage. For these the averages are
only for the tornadoes with an EF rating of F3 or higher. All three length averages seemed to be
roughly the same. With the widths, there were some differences, with the below normal and
normal temps both being right at or smaller then the above normal groups average width by
about a good 100 yards or so. With the injuries it was the opposite of that, with above normal
and normal both having less injuries occur per tornado compared to below normal with 37.69
people getting injured per tornado. Deaths were the same as injuries, with below normal having
the highest average, with 2.34 deaths per tornado. Finally looking at the average damage caused
by every tornado per group, you can see that when the temperatures are above normal, an F3 or
higher tornado is going to cause way more significant damage than any other time with the
average damage being $400 million plus per tornado, and then next highest was normal with
only $40 million plus per tornado. With these averages it was hard to tell which group had the
most intense tornadoes. So I decided to look at each group individually and show the averages
for F3, F4, and F5 tornadoes (Table 3, Table 4, Table 5).
Table 3: Above Normal Temp Tornadoes
F3 – 273 Tornadoes
Length – 17.18 Miles
Width – 478.7 Yards
Injuries – 6.7 People
Deaths - .3 People
Damage - $450,000,000+
F4 – 76 Tornadoes
Length – 28.21 Miles
Width – 609.5 Yards
Injuries – 17.4 People
Deaths – 1.3 People
Damage - $600,000,000+
F5 – 14
Length – 31.8 Miles
Width – 1126.4 Yards
Injuries – 159.2 People
Deaths – 22.6 People
Damage - $1+ Billion
20
Table 4: Normal Temp Tornadoes
F3 – 861 Tornadoes
Length – 18.3 Miles
Width – 388.6 Yards
Injuries – 10.3 People
Deaths - .4 People
Damage - $500,000+
F4 – 259 Tornadoes
Length – 26.25 Miles
Width – 559.56 Yards
Injuries – 51.1 People
Deaths – 3.5 People
Damage - $500,000,000+
F5 – 33
Length – 41.68 Miles
Width – 672.6 Yards
Injuries – 209.7 People
Deaths – 20.8 People
Damage - $1+ Billion
Table 5: Below Normal Temp Tornadoes
F3 – 267 Tornadoes
Length – 17.43 Miles
Width – 366.7 Yards
Injuries – 11.2 People
Deaths - .5 People
Damage - $400,000+
F4 – 123 Tornadoes
Length – 28.6 Miles
Width – 449.3 Yards
Injuries – 73.1 People
Deaths – 4.9 People
Damage - $600,000+
F5 – 17
Length – 32.69 Miles
Width – 522.6 Yards
Injuries – 197.8 People
Deaths – 12.2 People
Damage - $300,000+
Looking at these tables it is a little clearer but there still really is not definite group that
seems to be more intense than another. Breaking down each group’s separate categories we
could say that the above normal group has a significantly higher average of damage per year,
with the smallest only being at $450,000,000 per tornado. Other than that all of the averages for
each category seem to roughly be the same, with only a few outliers and that being above normal
F5 width at 1126.4 yards and also the injuries during the above normal years seemed to be less
than the other groups.
To see if there were any changes or directional change in where these tornadoes touched
down I found the mean center for each of the three groups and also the directional distribution
ellipse for all three groups. All three of the groups had their mean center land in the western
21
region of Missouri and within 75 miles of each other with the below normal mean center being
the farthest north away from the other two.
Figure 8: Above Normal Mean Center
Figure 9: Normal Mean Center
22
Figure 10: Below Normal Mean Center
After seeing hardly any change with their mean centers, I decided to make a density map
to see where the tornadoes were most dense throughout my study area for my three different
groups. For the above normal years the tornadoes seemed to cluster in mainly Kansas and a little
bit in eastern Iowa and western Wisconsin. For the normal years the tornadoes seemed to cluster
in a circle around the Midwest with a hole in Missouri which would be the area of the Ozarks.
Finally for the below normal years the tornadoes seem to cluster mainly in eastern Nebraska with
mini clusters elsewhere.
23
Figure 11: Above Normal Density
Figure 12: Normal Density
24
Figure 13: Below Normal Density
25
IV. Discussion
The results of this thesis were rather surprising after all of the data analysis was done. My
original hypothesis was that I believed that when the temperatures were above normal for my
study area, that the frequency and the intensity of F3 or higher tornados would be greater. As for
the frequency part of those F3 and higher tornadoes, it seems as though I was incorrect in my
hypothesis. As we can see form Table 2 that the F3 and higher tornadoes, although not by much,
did happen at a greater percent then the other two groups, and also the above normal groups
percents were the lowest with the exception of F5 being .1% higher than the normal’s F5
percentage. After seeing this result come up, I tried to figure out why. Perhaps this is because the
number of years in each group, with less years possible the percent would be higher because the
amount of overall tornadoes would be less. As the below normal group only covered 10 years of
data, where the above normal group covered 14 and the normal group had 36 years of data. I
think though that this result is true, because for F5 tornadoes there were 17 that occurred in the
10 years for the below normal group. With four more years of tornadoes for the above normal
group, only 14 F5 tornadoes occurred and with almost four times as much data the normal group
still had not even double the amount the below normal group had with only 33 F5 tornadoes. For
F4 and F3 tornadoes, the number of tornadoes differs but we see more F4 tornadoes for below
normal, with 123, than above normal, with 76, and the F3 tornadoes for these groups are almost
the same.
To determine which groups tornadoes were more intense is more difficult. It mainly
depends on how you would classify as an intense. You could say the wider and longer could be
more intense, the more people that got injured or died could mean more intense, or you could say
that tornadoes that caused more damage would be more intense. It could be any of the options or
26
even a combination of those options, but for the purpose of my thesis and for trying to give an
answer to my hypothesis, I am going to try and combine all of the elements and then see which
group could be having the more intense tornadoes. To do this I will first break down each of the
categories and go through them individually and try to find a clear winner for each, then total up
the score and see which group came out on top.
Length
Starting with the length of the tornadoes, as we can see from Table 2, the average lengths
for the three groups are pretty much close to the same, with below normal having the highest by
about a mile or so with an average of 21.4 miles per tornado. So from that table it is hard to tell
which group would come out on top, so we have to look closer and that would be with Tables 3,
4 and 5. From these tables we can see that the length of the tornado tracks for the F3 and F4
tornadoes are all roughly the same, they only differ from a mile to a couple miles from each
other, which would not be that significant. For the F5 tornado tracks we can see a bigger change,
both the below normal and above normal groups had an average of around 32 miles, were as the
normal group had an average of 10 miles greater with 42 miles. That 10 miles although may not
seem that significant, when you plot out 10 miles on a map that could be the difference between
an F5 tornado hitting a town and destroying it or a tornado lifting early and sparing the town.
With these results for the length of tornadoes when the temperature is above or below normal we
can say that the intensity of the lengths of the tornado tracks are going to be smaller in miles
compared to when the temperature is just normal.
Width
At first glance we can see that when it comes to the width category for these groups there
is a definite difference in these tornadoes. It is clear that when the temperature is above normal
27
you are going to have tornadoes on average with a width of 50 to 100 yards bigger than the other
two groups and with the F5 tornadoes they are going to be almost double the other two groups
with an average of about 1126 yards per tornado. It hard to say what could be the possible cause
of this, as tornadoes are so complex in the way they are formed. If I was going to base the
intensity of tornadoes solely off of the size of them, the clear winner in this category would be
above normal, as the size of these tornadoes were much larger on average compared to the other
two groups.
Injuries and Death
Overall, on average the below normal group had more injuries and deaths per tornado
than the other two groups. I think this is because of when the below normal years happened, as
with only three years in the 90’s, the rest of the seven years happened before 1984. Which back
then we did not really know much about tornadoes and our radar for detecting them and our
warning systems that we would give to the impacted people were not as advanced as they
became in the 90’s and what they are today. Taking that into account I think we can say that even
though during those years the average number of injuries and deaths per tornado were higher,
due to the lack of radar and warning systems we can say that these numbers are not that
significant. Along with that we can also say that since most of the years in all three groups minus
the last decade fall within the time when we had a lack of advanced radar and warning systems
that we cannot use the injuries and deaths in determining the intensity of tornadoes.
Damage
Part of how a tornado is classified is by looking at the amount of damage that it cause to
the area it passed over. Again looking at the data, we can clearly see that there is a winner in this
category, and that winner is the above normal group. As the smallest amount of damage that this
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group cause is $450 million and with F5’s causing on average over $1 billion dollars in damage
we can say that this group causes more damage than the other two groups. We can also see that
the below normal group has a significantly lower amount of damage per tornado than the other
two groups, with the highest being only $600,000. One thing to also not for the damage is also
the change in the value of a dollar, as in 1960 the dollar is going to be much less that what it
would be in 2005, so for the damage we also have to keep this fact in mind.
After going over all of the categories and we can see that the length and the injuries and
death are either closer enough to be the same or we cannot use them in our intensity equation
because of other factors, which leaves us with the width and the damage. Both of these
categories were won by the above normal temperature group. So from this I can say that that part
of my original hypothesis, that warmer than normal temperatures would cause tornadoes to be
more intense, is indeed correct. That whenever the average temperature is going to be above the
normal average, tornadoes on average are going to be greater in size, cause significant amounts
of damage and therefore be more intense.
The density of these different groups really did not change much; the biggest cluster was
either in Nebraska or Kansas, the heart of tornado alley. For the above normal group there
seemed to be a bit more clustering of tornadoes throughout the study area but mainly just to the
north and also right in the heart of tornado alley. For the normal group there seemed to be a big
circle of clusters with the center being in the middle of Missouri, but again the major clustering
was in the heart of tornado alley. Finally the below normal group did not have much clustering,
only one real big cluster, which was again in the heart of tornado alley. I would expect all of
these maps to show what they did, as tornado alley should have the majority of the tornadoes as
this is the best place in the world for tornadoes to occur.
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V. Conclusion
It is apparent that through this study we can come to a couple conclusions. We can
conclude that when the temperature is above normal F3 or higher tornadoes are not going to
happen more frequently, but rather when the temperature is below normal F3 or higher tornadoes
will happen more frequently. We can conclude that when the temperature is above normal the
intensity for F3 or higher tornadoes is going to be more intense and on average the size of the
tornadoes will be larger and the damage will be much more significant. With a lot still unknown
about tornadoes and how they form and react to the environment, I cannot fully say that the
results from this study will continue to hold as each year passes, or at least until we have a better
understanding of tornadoes themselves.
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VI. Recommendations
If future research were to be done it would be recommended to maybe use a smaller study
area, and just look at the true tornado season. Also as our knowledge of tornadoes progresses, it
would be recommended to expand what aspects to look at for each tornado and to come up with
a new way to figure out how to calculate the intensity of a tornado.
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VII. Acknowledgements
First I would like to thank my thesis advisor Dr Matt Zorn. Next I would like to thank Dr
Joy Mast for helping me with the proposal of my thesis. I would also like to thank Prof Wenjie
Sun for all her help with the GIS part of my thesis. Next I would like to thank all of my
classmates with their input and help during the beginning process of my thesis. Finally I would
like to thank my friends and family for all their support they gave me during the process of
writing up my thesis. Thank you all.
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References
Christopherson, Robert W. Geosystems: an Introduction to Physical Geography. Upper Saddle River, NJ:
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Diffenbaugh, N. S., R. J. Trapp, and H. Brooks. "Does Global Warming Influence Tornado
Activity?" EOS 89.53 (2008): 553-60. Print.
Douglas, Paul. Restless Skies: the Ultimate Weather Book. New York: Sterling Pub., 2005. Print.
Hyndman, Donald W., and David W. Hyndman. Natural Hazards and Disasters. Australia:
Brooks/Cole, 2009. Print.
Karl, Thomas R., Richard W. Knight, David E. Easterling, and Robert G. Quayle. "INDICES OF
CLIMATE CHANGE FOR THE UNITED STATE." Bulletin of the American
Williams, Jack. The AMS Weather Book: the Ultimate Guide to America's Weather. Chicago:
University of Chicago, 2009. Print.
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