Tornadoes Per 100 Square Miles Per County, 1950-2010

I used the NCDC Storm Events database and Severeplot 3.0 to construct this map. Since each county varies in size, we have to try to level the playing field.  To that end, I did some calculations to find the number of tornadoes per 100 square miles per county from 1950-2010.  Here is what I found:

Not surprisingly, population bias is pretty noticeable.  It's not a perfect relationship but there is a general tendency for higher populated counties to report more tornadoes which makes sense.  More people=greater chance of someone seeing it.

Here are the top 5 counties in terms of tornadoes per 100 square miles:

Marion - 10.35
Tippecanoe - 8.40
Vanderburgh - 7.67
Shelby - 7.03
Elkhart - 6.90


Here are counties ranked by population. Notice that 4 of the above listed counties appear in the top 8 (out of 92) in terms of population. Curiously, Shelby county ranks much farther down on this list.

1. Marion
2. Lake
3. Allen
4. Hamilton
5. St. Joseph
6. Elkhart
7. Vanderburgh
8. Tippecanoe
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32. Shelby