Tornado's

Outline for Informative Speech

Your name

Tornadoes

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

I. Introduction

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.

II. Body

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 tornadoes

1. 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 tornadoes

i. Account for 69% of all tornadoes.

ii. Winds are less than 110mph.

b. Strong tornadoes

i. Account for 29% of all tornadoes.

ii. Winds range from 110 to 205 mph.

c. Violent tornadoes

i. 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 Oddities

1. Stories of strange events are typical in the wake of the damage caused by tornadoes. Indeed,