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The Day the Sky Roared Shortly after daybreak on April 3, 1974, thunder began to rumble through the dark skies that covered much of the midwestern United States. Lightning struck areas from the Gulf Coast states to the Canadian bor- der. By the predawn hours of the next day, the affected region of around 490,000 acres was devastated by over 100 tornadoes. This “ super outbreak ” was responsible for the deaths of over 300 people in 11 states. More than 6100 people were injured by the storms, with approximately 27,500 families suffering some kind of loss. The total cost attributed to the disaster was more than $600 million. Amazingly, the storm resulted in six Category 5 tornadoes with wind speeds exceeding 261 miles per hour. To put this figure in perspective, the region endured about one decade ’ s worth of Category 5 tornadoes in a single 24-hour period! CASE STUDY Fujita Wind Damage Scale F-Scale Wind Speed Damage Tornado Duration Times for Outbreak of April 3 – 4, 1974 F-Scale Tornado Duration (minutes) Structural engineers and meteorologists are interested in understand- ing catastrophic events such as this tornado outbreak. Variables such as tor- nado intensity (as described by the F-Scale), tornado duration (time spent by the tornado in contact with the ground), and death demographics can provide insights into these events and their impact upon the human popula- tion. The following data list the duration time and F-Scale for each tornado in the April 1974 Super Outbreak: F-0 Up to 72 mph Light F-1 73 to 112 mph Moderate F-2 113 to 157 mph Considerable F-3 158 to 206 mph Severe F-4 207 to 260 mph Devastating F-5 Above 260 mph Incredible F-0 1,1,5,1,1,6,4,10,5,4,1,1,1,1,1,1,1,1,1,30,1,9 F-1 16,13,9,8,13,10,15,1,17,23,10,8,12,5,20,31,12,5,30,13,7,1,5,13,1,2,5,10, 1,20,5 F-2 7,15,2,10,23,10,7,12,8,1,8,19,5,10,15,20,10,13,20,15,13,14,1,4,2,15,30, 91,11,5 F-3 9,20,8,16,26,36,10,20,50,17,26,31,21,30,23,28,23,18,35,35,15,25,30,15, 22,18,58,19,23,31,13,26,40,14,11 F-4 120,23,23,42,47,25,22,22,34,50,38,28,39,29,28,25,34,16,40,55,124,30, 30,31 F-5 37,69,23,52,61,122 SullStatCH02_Fpp50-109 11/20/02 10:17 AM Page 106 Create a report that graphically displays and discusses the tornado- related data. Your report should include the following: 1. A bar graph or pie chart (or both) that depicts the number of tornadoes by F-Scale. Generally, only a little more than 1 percent of all tornadoes exceed F-3 on the Fujita Wind Damage Scale. How does the frequency of the most severe tornadoes of the April 3 – 4, 1974, outbreak compare with normal tornado formation? 2. A single histogram that displays the distribution of tornado duration for all of the tornadoes. 3. Six histograms displaying tornado duration for each of the F-Scale categories. Does there appear to be a relationship between du- ration and intensity? If so, describe this relationship. 4. A bar chart that shows the relationship between the number of deaths and tornado intensity. Ordinarily, the most severe tornadoes (F-4 and F-5) account for more than 70 percent of deaths. Is the death distribu- tion of this outbreak consistent with this observation? 5. A bar chart that shows the relationship between the number of deaths and community size. Include a discussion describing the number of deaths as a function of community size. 6. A general summary of your findings and conclusions. Data Source: Abbey, Robert F. and T. Theodore Fujita. “ Tornadoes: The Tornado Outbreak of 3 – 4 April 1974. ” In The Thunderstorm in Human Affairs , 2nd ed, edited by Edwin Kessler, 37 – 66. Norman, OK: University of Oklahoma Press, 1983. The death figures presented in this case study are based on approximations made from charts by Abbey and Fujita. Additional de- scriptions of events and normal tornado statistics are derived from Jack Williams ’ s The Weath- er Book . (New York: Vintage Books, 1992.) 107 Deaths as a Function of F-Scale for April 3 – 4, 1974, Tornadoes F-Scale Deaths F-0 0 F-1 0 F-2 14 F-3 32 F-4 129 F-5 130 The following tables present the number of deaths as a function of F-Scale and community size: Deaths as a Function of Community Size for Tornado Super Outbreak of April 3 – 4, 1974 Community Size Deaths Rural areas 99 Small communities 77 Small cities 63 Medium cities 56 Large cities 10 SullStatCH02_Fpp50-109 11/20/02 10:17 AM Page 107
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The data can be also shown in the pie chart below;



In the tornado outbreak of April 3-4, 1974 the most severe tornadoes overpass the normal tornado f