Article on tornado trends showing decrease for the plains and increase for midwest and southeast

May 18, 2013
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I case you had trouble with the link Bill posted like I did, here is another one to the Gensini and Brooks paper on "Spatial trends in United States tornado frequency": https://www.nature.com/articles/s41612-018-0048-2

Here is the abstract of that paper:
"Severe thunderstorms accompanied by tornadoes, hail, and damaging winds cause an average of 5.4 billion dollars of damage each year across the United States, and 10 billion-dollar events are no longer uncommon. This overall economic and casualty risk—with over 600 severe thunderstorm related deaths in 2011—has prompted public and scientific inquiries about the impact of climate change on tornadoes. We show that national annual frequencies of tornado reports have remained relatively constant, but significant spatially-varying temporal trends in tornado frequency have occurred since 1979. Negative tendencies of tornado occurrence have been noted in portions of the central and southern Great Plains, while robust positive trends have been documented in portions of the Midwest and Southeast United States. In addition, the significant tornado parameter is used as an environmental covariate to increase confidence in the tornado report results."

USA Today also published a story on this paper today: https://www.usatoday.com/story/weather/2018/10/17/tornado-alley-shifting-east/1660803002/
 

rdale

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My concern is the media equating "trends in STP" to "trends in tornadoes." My joke about Michigan is part of it - showing that we get more STP in the summer months than before, therefore concluding that Michigan gets more tornadoes, doesn't match actual tornado counts. And I totally get the concern with the changing patterns, and the history of tornado counts, but 14 of the last 20 years have been below normal in Michigan. And the ones that have occurred are often in areas that were NOT counted before (rural spots in northern Michigan have been the hotbed lately,) Concluding that actual tornadoes are moving where STP moves is strange.
 
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My concern is the media equating "trends in STP" to "trends in tornadoes." My joke about Michigan is part of it - showing that we get more STP in the summer months than before, therefore concluding that Michigan gets more tornadoes, doesn't match actual tornado counts. And I totally get the concern with the changing patterns, and the history of tornado counts, but 14 of the last 20 years have been below normal in Michigan. And the ones that have occurred are often in areas that were NOT counted before (rural spots in northern Michigan have been the hotbed lately,) Concluding that actual tornadoes are moving where STP moves is strange.
The research article does have data for both STP and tornado reports, so it does not rely entirely on STP. Also it makes the point that the incidence of tornadoes remains higher in some of the Great Plains area where the trend is down than the incidence of tornadoes farther east where it is rising. Of course some of this gets lost in the media coverage.
 

Jeff Duda

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I agree that I'm not fully sold that you can use the "annual sum of daily max STP" as a true covariate for tornado occurrence. The correlation coefficient values in the paper were disappointingly low overall (annual STP vs. annual tornadoes was only 0.44; the highest monthly correlation between summed daily max STP and tornado count was 0.65 in February and the correlation of the big 3 months ranged from 0.39 to 0.54; with the exception of the 0.65, these are pretty weak correlations, even if the positive slope is statistically significant).

It's good that they included Fig. 5, which is pretty much the most believable highlight of the paper. It shows that tornado report trends are indeed increasing east of the Mississippi, with a local maximum near the Miss./Ohio River valley intersection. There are also scattered areas of decreases in Texas, NE Colorado, and parts of the upper Midwest.

I'm not saying I don't think there is a change in the spatial distribution of yearly tornadoes. However, I'm not 100% sure that the environmental metric they used (annual sum of daily max STP) is the best one available to correlate with tornado occurrence.
 
Jun 18, 2017
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Tennessee
As someone living in the South, I thought that is interesting to consider, and I’d like to see how it unfold in next decade or so. While it’s a concerning study for a Southerner, I’d still take it with a grain of salt.
 
Aug 22, 2015
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Hastings, Nebraska
When doctor Greg Forbes spoke at my college I asked him about this issue and he believes that this increase in climatic temp overall is driving more cases of nocturnal acceleration of the LLJ as well as higher moisture
 
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