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Officials cite drought for tornado decline

October 4, 2005

BY JAN DENNIS ASSOCIATED PRESS

Fewer than half of Illinois' usual number of tornadoes have touched down so far this year, held back by a lingering drought that eased last month after remnants of Hurricane Rita helped shower much of the state with above-average rainfall, weather officials say.

Only 16 tornadoes were reported through September, which would make 2005 the sixth-slowest year for twisters since 1975 if none spin up during the typically quieter last three months of the year, said Chris Miller, a meteorologist with the National Weather Service in Lincoln.

More:
http://www.suntimes.com/output/news/tornado04.html
 
Ahem....well below normal precipitation was the story of the summer for much of Wisconsin as well:

stoughton-c.jpg


Contrast that with the spring/summer of 2004 which was extremely wet with many flooding problems, and that year also produced a way above average number of tornadoes.

Now I'm REALLY confused about the relationship between tornadoes/other svr wx and rainfall amounts.
 
Just a caution... This may be a chicken or egg issue here. I mean, if there's very limited convection, rainfall amounts over some time will likely be limited as well. So in that respect, it may be a lack of convection that led to the drought. On the other hand, dry conditions (drought) may have resulted in lower-than-climo surface dewpoints (owing to less evapotranspiration and regular evaporation I suppose), which can feed back into limiting convection. Regardless, there is some interaction issue between convection and drought conditions. Of course, I'm making a huge assumption here, in that if you have more convection, you'll have more tornadoes. Of course this is a very crude assumption, but it's likely valid enough over the time range of 4+ months. Note also that I'm holding location constant (so I'm not assuming FL should have more tornadoes than IL because they have more "thunderstorm days", but rather that IL has fewer tornadoes when they have fewer thunderstorm days / more tornadoes when they have more thunderstorm days). Granted, it's also important to remember that one single outbreak (freakish or not) can easily "make or break" the tornado count.
 
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