Photo: Infared satellite image of hurricane Rita

Infrared satellite image of hurricane Rita

Satellite image courtesy of NOAA

Download this activity as a PDF.

Springtime may bring the promise of April showers and May flowers. But it also brings the possibility of extreme weather, including violent thunder-storms and tornadoes.

Most countries experience tornadoes, but they occur more frequently in the United States, east of the Rocky Mountains, than anywhere else on Earth. On average, almost 1000 tornadoes touch down in the U.S. each year, leaving in their wake destruction and sometimes death.

How Tornadoes Form

Thunderstorms form when warm, moist air collides with an eastward moving cold front. These storms often produce strong winds, damaging hail, and even tornadoes. A tornado is a rapidly rotating column of air that extends from the base of a thunderstorm to the ground. A tornado’s characteristic funnel shape is visible because of water droplets, dust, and other debris that are caught up in the swirling air.

Measuring the Force of a Tornado

The force of a tornado is measured using the Fujita Scale, which ranks tornadoes based on the level of damage caused by the storm. The scale ranges from F-0 for a storm that causes light damage to F-5 for a storm that leaves incredible damage.

Mapping Tornado Frequency in the U.S.

a)  Distribute to students copies of the handout. Have student examine the data in the handout to identify which states average the highest number of tornadoes each year.

b)    Next, distribute blank U.S. maps. Have students construct choropleth maps showing the frequency of tornadoes by state in the U.S.

c)    Explain to students that areas with a high occurrence of tornadoes have been given the nicknames of “Tornado Alley” and “Dixie Alley.” Have them refer to their maps to locate these two regions that experience many tornadoes each year.

Extending the Activity

Divide the class into three groups and assign each group one of the following research topics. When students have completed their research, have each group report back to the class.

i. Structure of a tornado

ii. Fujita Scale

iii. Tornado Alley/Dixie Alley

See the NOAA National Severe Storms Laboratory and the Tornado Project for more information.


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