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Conditions for Frequent Tornado Events
Name: Susan
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Thank you for all of your support! I had asked you
questions in the past and you were so timely and helpful. Why do
tornadoes happen more in the Midwest of the United States? Students
came up with it is because the land is flatter. Thought I should
check it with the experts.
Replies:
Susan,
Tornadoes occur mostly in the plains states east of the Rocky
Mountains and in the early Spring they occur primarily in
association with cold fronts moving through the southeastern
United States. Most people do not realize that the center
of activity for early Spring thunderstorms and tornadoes is the
southeast. Later, the center of activity moves to the
southern plains states and in late Spring and early summer
it moves to the central, northern, and eastern plains states
(Midwest - Iowa, Illinois, Minnesota, Michigan, Ohio).
The reason for this is, primarily, the position of the
jet stream and associated warm and cold fronts. As Spring
progresses, the jet stream moves westward and northward in
response to surface warming that starts in the south and
progresses westward and northward.
The convection that feeds severe thunderstorms is most easily
started in flatter terrain. More hilly or mountainous terrain
disrupts the convective process, but it is not the
most important factor in the development of severe
thunderstorms and tornadoes. Vertical wind shear, which the
jet stream provides in abundance, is needed to spawn
a tornado.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012
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