Cause for Geographic Tornado Distribution
Why do so many tornados form in the midwest United States?
(vs. not many in Europe for example).
The middle part of the US is just right for tornados.
It is flat.
It gets very hot.
It has very fast changing weather.
Europe is too far north to get hot enough. If you look at a globe you will see how
far north compared to say, Kansas or Oklahoma. Actually, Europe can get tornados,
but they are so rare no one worries about them. Russia which is flat enough doesn't
get hot enough, just like Europe.
There are a couple of answers on the Ask-A-Scientist site
that can provide more detailed reasons, but basically,
the reason is primarily the unique geography of the central
United States of America. The Rocky Mountains form a very long
north-south barrier to air flowing from west to east (which causes
the air to dry as it drops water within the Rockies and warms
as it descends from the eastern edge of the mountains),
the Plains states east of the Rockies provide a strong heat
(and sometimes moisture) source, the normal wind direction
pattern in Spring and Summer brings moist air at mid-levels
of the atmosphere from the Gulf of Mexico into the central
part of the country, and the jet stream typically aligns itself
from southwest to northeast in the Plains states. These
characteristics are not necessarily completely independent of
each other, but they combine to provide the right conditions
to produce strong squall lines with embedded thunderstorms,
as well as isolated supercell thunderstorms.
You may notice one of my answers in Ask-A-Scientist that
explains the strong thunderstorm activity in the Southeast
during early to late Spring, whereas the strongest thunderstorm
activity in the Plains states occurs in late Spring and early
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012