For those not aware...the following link from NOAA's Storm Prediction 
Center has some
climatology on Severe Wx/Tornado across the US.
http://www.spc.noaa.gov/climo/

If you go through the links within this page, you'll find some very 
interesting data available.

Enjoy,
Scott

-- 
Scott L. Whittier
Senior Meteorologist               DOC/NOAA/National Weather Service
[log in to unmask]            Burlington Intl Airport
802-862-2475 x239                  1200 Airport Drive
www.weather.gov/btv                S. Burlington VT 05403-6028
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The contents of this message are mine personally and do not
necessarily reflect any position of the Government or the National
Oceanic and Atmospheric Administration.