Getting Geographic: Martha’s Study Corner April 19, 2011 Tracking Violent Storms Vol. 1: #16

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 Courtesy NOAA National Severe Storms Laboratory with an eastward moving cold front. These storms often produce strong winds, damaging hail, and b) Next, distribute blank U.S. maps [available at even tornadoes. A is a rapidly rotating education.nationalgeographic.com/education/ma column of air that extends from the base of a pping/outline-map/?map=USA]. Have students thunderstorm to the ground. A tornado’s construct choropleth maps showing the characteristic funnel shape is visible because of frequency of tornadoes by state in the U.S. water droplets, dust, and other debris that are caught up in the swirling air. c) Explain to students that areas with a high occurrence of tornadoes have been given Measuring the Force of a Tornado the nicknames of “” and “ Alley.” Have them refer to their maps to The force of a tornado is measured using the locate these two regions that experience Fujita Scale, which ranks tornadoes based on the many tornadoes each year. level of damage caused by the storm. The scale ranges from F-0 for a storm that causes light Extending the Activity damage to F-5 for a storm that leaves incredible damage. Divide the class into three groups and assign each group one of the following research topics. Mapping Tornado Frequency in the U.S. When students have completed their research, have each group report back to the class. a) Distribute to students copies of Activity 16 – Handout #1. Have student examine the data i. Structure of a tornado in the handout to identify which states ii. Fujita Scale average the highest number of tornadoes iii. Tornado Alley/Dixie Alley

each year. See the NOAA Severe Storm web site and the Tornado Project for more information.

Activity #16 – Handout 1

Average Number of Tornadoes in the United States, by State, 1953-2004

Average Number of Average Number of State State Tornadoes per Year Tornadoes per Year 25 Nebraska 45 Alaska 0 Nevada 1 Arizona 4 New Hampshire 2 25 New Jersey 3 California 5 New Mexico 9 Colorado 22 New York 7 Connecticut 1 19 Delaware 1 North Dakota 22 Florida 55 Ohio 15 22 Oklahoma 57 Hawaii 1 Oregon 2 Idaho 3 Pennsylvania 12 Illinois 35 Rhode Island 1 Indiana 22 14 Iowa 37 South Dakota 29 55 15 12 139 27 Utah 2 Maine 2 Vermont 1 Maryland 6 Virginia 10 Massachusetts 3 Washington 2 Michigan 17 West Virginia 2 Minnesota 25 Wisconsin 20 27 Wyoming 11 30 Montana 7

Source: NOAA/National Climatic Data Center, available at http://www.ncdc.noaa.gov/img/climate/research/tornado/avgt5304.gif