TORNADO ALLEY

Carl Miller

Preview of Main Ideas

Tornadoes, often devastating and sometimes deadly, are violent rotating columns of air that descend to the earth during severe thunderstorms activity. Twisters, as tornadoes are often called, occur in various countries around the world; but no other country in the world receives more tornadoes than the United States. States in the south central area of the United States experience the greatest number of tornadoes, thus the name “Tornado Alley.”  Conditions for the violent windstorms in this region are often time ideal. When cool, dry air from the north meets warm, moist air from the Gulf of Mexico, tornadoes are frequently the result of this meeting. Texas, with an annual average of approximately 130 tornadoes, is an example of what can happen when the two distinct air masses collide.

Classification with the Curriculum

This activity can be used in a geography or science class.

Teaching level: Grades 5-8.

Objectives Classification Outline (Also see objectives classification matrix below.)

Objective #1: The student will describe the conditions necessary for the formation of a tornado.

Essential Element: Physical Systems.

Standard #7: The physical processes that shape the patterns of the Earth’s surface.

Knowledge statement #2: How Earth-Sun relationships affect physical processes and patterns on Earth.

Skill Set #1: Asking geographic questions.

Skill #2: Plan how to answer geographic questions.

Theme: Place.

Objective #2: The student will be able to identify the region of the United States known as Tornado Alley.

Essential Element: Places and Regions.

Standard #4: The physical and human characteristics of places.

Knowledge Statement #1: How different physical processes shape places.

Skill Set #4: Analyze Geographic Information.

Skill #1: Interpret information obtained from maps, aerial photographs, satellite-produced images, and geographic information systems.

Theme: Region.

Objective #3: The student will be able to construct a choropleth map from a given set of data.

Essential Element: The world in spatial terms.

Standard #1: How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information from a spatial perspective.

Knowledge Statement #2: How to make and use maps, globes, graphs, charts, models, and databases to analyze spatial distribution and patterns.

Skill Set #4: Organize geographic information.

Skill #1: Prepare various forms of maps as a means of organizing geographic information.

Theme: Location.

Materials

Outline map of the United States.

Set of four markers (preferably brown, red, orange, and yellow).

Atlas.

Tornado Occurrence data sheet.

Instructions for creating a choropleth map.

Suggestions for Teaching the Lesson

Opening the Lesson

1. Begin the lesson by discussing with the students the factors that are responsible for the formation of tornadoes. Tell the class that certain regions of the United States are much more likely to have tornadoes than are other regions. Discuss with the students ways in which they might be able to identify the regions having the greatest number. Introduce the concept of choropleth maps and ability of the map to display certain information.

2. Divide the class into groups of 2 or 3 students.

3. Distribute to the different groups a blank outline map of the United States, a set of markers, and the Tornado Occurrence data sheet.

Developing the Lesson

1. Discuss with the students the procedure for dividing the tornado data into class intervals. Refer to the choropleth mapping sheet included with this lesson.

2. Assign colors to the different intervals: highest group, brown; second group, red; third group, orange; fourth group, yellow. Choose colors that range from dark for highest values to light for lower values

3. Complete the maps by coloring the states on the map with the appropriate colors. Encourage the students groups to be alert for certain color patterns that may occur on their maps as they complete the coloring process.

4. After the coloring process is complete, students should be encouraged to add the essential elements to the map, i.e., title, legend, author, date, and source information.

5. Identify the large brown area of the map as the region known as Tornado Alley.

6. Discuss with students the reasons for the large number of tornadoes that occur in this area of the United States. At this point, the relative location of the region should be discussed. The fact that the region’s weather is influenced by the warm, moist air from the Gulf of Mexico to the south and the cool, dry air from the north is crucial to the weather patterns of the region. These two factors are the most influential in causing the many tornadoes that occur in the region.

Concluding the Lesson

1. Ask students to identify ways in which the lives of the residents from this Tornado Alley region might be different from those of people in other regions of the United States.

2. Discuss what precautions might be taken by the residents of the area in order to prevent loss of life and extreme property damage. Suggestions might possibly include tornado safety drills while at school, identifying a safe shelter somewhere in their home, and methods to make mobile homes tornado-proof such as anchoring the home to the ground.

3. Display the students’ maps in an area of the room or school where they may be seen by other classes.

Extending the Lesson

Students could investigate and map other significant weather phenomena, e.g., snowfall and hurricanes. Explanations for increased frequencies and amounts can be discussed.

Assessing Student Learning

1. Student maps will be examined for completeness and accuracy.

2. Have students describe in writing the causes for the formation of a tornado and list the region of the United States that is most tornado prone and those regions that are least likely to experience a tornado.

GEOGRAPHY STANDARDS CLASSIFICATION MATRIX – GRADES           5-8   

Title:          Tornado Alley          Author:     Carl Miller

Note:  See also Objectives Classification Outline in the lesson.

Handouts

Handout A

CHOROPLETH MAPPING

The following procedure is recommended for constructing a choropleth map.  It can be used with any data that ranges in value and can be associated with geographic regions, e.g. counties, states, countries.

1. Determine class intervals by first finding the range of the data.  Select the number of classes to be used for your map and calculate the interval of each class.  Here is one method for determining class intervals.
   a.    Inspect your data sheet to identify extreme values, such as the number of tornadoes in Texas.
   b.    Eliminate extreme values for purposes of calculating range in the data.
   c.    To calculate range, determine the highest and lowest values in the data.
   d.    Subtract these two numbers in order to calculate the range for the data.  Be sure to exclude data for Texas
          before calculating ranges, but include it in the highest group for mapping.
   e.    Divide the range by the number of classes planned for your map.  Three to seven mapping classes will be
          adequate for most data sets.  Experiment with three and four intervals for the tornado data to determine which
          one provides the most useful mapped patterns.  The number produced by the division will be the range for each
          class.  (Note:  The best number of classes to use is the one that gives you the most useful information.  Generally,
          between three and seven works best.  If too few classes are used, important details may be lost.  Too many
          classes mean that the map gets cluttered with too much detail.)
          Example of class intervals:

                  The map maker may choose to adjust the classes if there are outliers or clusters of information that become
                   hidden in the process outlined above.
            f.    Often the highest and lowest classes will contain a larger interval because the range does not divide evenly.
                  Construct classes so that the numbers in one class do not overlap those in adjacent classes.

2. Arrange a color code or shading pattern for each class.  Colors or patterns should increase from light to dark, from lowest to highest class.

3. Identify the proper class interval for each country or region and color or shade the state on an outline map.  Title the map, place a legend on the page, and include the source for the data displayed.

4. If other data sets (e.g., precipitation amounts) are mapped to find relationships, students should consider the following as they complete their analysis.
   a.    Describe the patterns observed on the maps.
   b.    What accounts for the variation?
   c.    Discuss the factors that could lead to the range of outcomes within the distribution.
   d.    Discuss the relationships between the regional patterns.  Is the relationship positive or negative?  (Are the states
          with the highest rate of one variable the same states with the highest rate of the other variable?  If so, there is a
          positive correlation.  if the states that are highest in one variable are lowest in another, the correlation is
          negative.)
   e.    Discuss whether or not the factors that contribute to the patterns in one variable affect the patterns of another.

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Handout B

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Handout C

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