Outline for Informative Speech
Purpose: To inform the audience about tornadoes.
Thesis: In order to better understand tornadoes, it is important to explore what causes tornadoes to develop, how researchers classify types of tornadoes, and odd occurrences that may be associated with tornadoes.
Organizational Pattern: Topical
A. Attention Getter: What can hurdle automobiles through the air, rip ordinary homes to shreds, defeather chickens, and travel at speeds over 60 mph?
B. Relevance: Illinois rests on the boundary of what tornado researchers call tornado alley. This is the area of the country that receives the most tornadoes every year. According to a 1995 brochure distributed by the National Oceanic and Atmospheric Administration (NOAA), Illinois averages 27 tornadoes a year. Also, nearly 5 people die every year in Illinois as a result of tornadoes [ AID]. In fact, according to Tornado Project Online!, a website hosted by a company that gathers tornado information for tornado re searchers, the deadliest tornado in U.S. recorded history occurred in Murphysboro, Illinois. In 1925 a violent tornado killed 234 people in this Southern Illinois town.
C. Credibility: I grew up in the heart of tornado alley and have been interested in this weather phenomenon for a very long time. Also, I am a trained weather spotter for the Bloomington/Normal civil defense agency.
D. Thesis: In order to better understand tornadoes, it is important to explore what causes tornadoes to develop, how researchers classify types of tornadoes, and odd occurrences that may be associated with tornadoes.
E. Preview: So, let's crash through the causes of tornadoes, twist around the types of tornadoes, and blow through some of the oddities associated with tornadoes.
Transition: Initially, I'll crash through the causes of tornadoes.
A. What causes tornadoes?1. According to the USA Today Tornado Information website, a tornado is a "violently rotating column of air in contact with the ground and pendant from a thunderstorm." Therefore, thunderstorms are the first step in the creation of a tornado.
2. The USA Today Tornado Information site also indicates that there are three key conditions for thunderstorms to form.a. First, moisture in the lower to mid levels of the atmosphere.
b. Second, unstable air. This is air that will continue rising once it begins rising from near the ground.
c. The finial condition for the formation of tornado-producing thunderstorms is a lifting force. A lifting force is a mechanism that cause the air to begin rising. The most common lifting force is heating of the air (which is why we experience so many thunderstorms in the spring as the air begins to warm).
3. The same source indicates that the strongest thunderstorms typically form in warm, humid air that's east or south of advancing cold air.
4. I mentioned in the introduction that Illinois sees its fair share of tornadoes. The following graph, adapted from the USA Today Tornado Information web site, illustrates areas in the U.S. that receive the greatest number of tornadoes (tornado alley). Thunderstorm-producing tornadoes are likely to form in this area as cold air from the west and north clashes violently with warm air from the Gulf of Mexico [AID].
Transition: Now that we have crashed through the causes of tornadoes, let's twist around the types of tornadoes.
B. Types of tornadoes1. According to renowned weather historian Dr. David Ludlum, author of the 1997 edition of the National Audubon Societies Field Guide to North American Weather, tornado researchers use a scale, known as the Fujita-Pearson Tornado Intensity Scale (named after its creators) to rate the intensity of tornadoes [ AID].
2. Tornado statistics from NOAA (cited above) [ AID]a. Weak tornadoesi. Account for 69% of all tornadoes.
ii. Winds are less than 110mph.
b. Strong tornadoesi. Account for 29% of all tornadoes.
ii. Winds range from 110 to 205 mph.
c. Violent tornadoesi. Represent only 2% of all tornadoes.
ii. Winds exceed 205 mph.
iii. According to Tornado Project Online!, although violent tornadoes account for only 2% of all tornadoes, they are responsible for 67% of all deaths in tornadoes [ AID].
iv. In addition, astrogeophysicist Dr. Robert Davies-Jones notes in a 1995 edition of Scientific American that most tornadoes have damage paths 150 feet wide, move at about 30 miles per hour and last only a few minutes. However, extremely violent tornadoes, like the one that ripped through Murphysboro,
d. Illinois, may be over a mile wide, travel at 60 mils per hour and may stay on the ground for more than one hour.
Transition: Now that we have a better understanding of the causes and types of tornadoes, I'll blow through some of the oddities associated with tornadoes.
C. Tornado Oddities1. Stories of strange events are typical in the wake of the damage caused by tornadoes. Indeed, much of what makes stories of tornadoes unusual is irony. Consider the following story from the 1996 Weather Guide Calendar. In a 1984 Kansas tornado a man, apparently thinking that his mobile home would be destroyed, ran to shelter in another building, only to have that building destroyed (killing the man), while his trailer survived just fine.
2. As noted by Tornado Project Online!, the Great Bend, Kansas tornado of November 1915 is a tornado which seems to have the greatest number of oddities associated with it.a. At Grant Jones' store, the south wall was blown down and scattered, but shelves and canned goods that stood against the wall were not moved.
b. The Riverside Steam Laundry, build of stone and cement block, was completely destroyed, yet two nearby wooden shacks were untouched.
c. A canceled check from Great Bend was found in a corn field, one mile outside of Palmyra, Nebraska.. .305 miles to the northeast. This is the longest know distance that debris has ever been carried.
3. Tornado Project Online! also reports that the "plucked chicken" remains today as perhaps the most talked about tornado oddity [ AID]. Indeed, this oddity has been associated with many Illinois torn a- does.a. Within the damage descriptions of rural tornadoes, there are often stories of a chicken "stripped clean of every feather."
b. It has long been thought that the feathers explode off the bird in the tornado's low pressure.
c. The most likely explanation for the defeathering of a chicken is the protective response called "flight molt." As noted by Tornado Project Online!, "chickens are not stripped clean, but in actuality they lose a large percentage of their feathers under stress in this flight molt process." In short, when the chickens become scared their feathers become loose and are simply blown off.
A. Thesis/Summary: In this speech I have explored the key factors that cause tornadoes to develop, how re searchers classify types of tornadoes, and odd occurrences that may be associated with tornadoes.
B. Memorable Close: So the next time you see a Ferrari flying through the air, your college dorm being dismantled floor by floor, or a chicken without wings, take cover because tornado season is here.
Davies-Jones, R. (1995). Tornadoes: The storms that spawn twisters are now largely understood, but mysteries still remain about how these violent vortices form. Scientific American. 273(2) 48-58.
Grazulis, T. (1995). Chasing tornado oddities. In L. Sessions (Ed.), 1996 Weather Guide Calendar with Phenomenal Weather Events Denver, CO: Accord Publishing.
Ludlum, D. M. (1997). National Audubon Society field guide to North American weather New York: Chanticleer Press.
National Oceanic and Atmospheric Administration. (1995). Tornadoes: Nature's most violent storms [ Washington, DC: National Weather Service.
Tornado Project Online. (2000, June 19). The top ten U.S. killer tornadoes [ Available: http:// www.tornadooroject.com]
USA Today Tornado Information. (2000, June 20). Understanding tornadoes [ Available: http:// www.usatoday.cornJweather/tomado/wtwistp.h
Contributed by Dr. Cheri Simonds & Dr. Stephen Hunt, Illinois State University