By Boris Konon, Meteorologist and Storm Chaser
Here are the most recent U.S. tornado statistics from the Storm Prediction Center (SPC).
October U.S. tornado count average is 61 (69 preliminary) and November averages is 58 (27 preliminary). Preliminary number for December so far is 29 and average is 24. That essentially appears to be it for the year. The 29 preliminary count this month is about 10 less for a final count when you remove duplicate reports from 12/23. Yearly U.S. average is 1253.
I estimate the final count for 2014 will be ~835. That is an extraordinary deviation from the mean. 67% of average, 6% lower than 2013 and 8% lower than 2012! This is the lowest count since 1988 when 702 tornadoes occurred. 1989 is second with 856.
Here is a graphic that shows “detrended” tornado counts over the years. This helps to account for the better detection and documentation of tornadoes over time. Not perfect, but better than just the raw numbers. Look at 2014...about two standard deviations below average!
In the last 15 years, we see more well below than well above average years. Another way of looking at it, there are more wild swings in the past 15 years. True, but the door swings both ways and unlike say precipitation (too wet or too dry) the lack of tornadoes is a good extreme regardless of how you look at it. So with tornadoes, the more wild swing hypothesis due to climate change cancels things out more or less in the long run. Yes, there will be big years and devastating outbreaks, but that is part of normal climatic variation. As we have seen, for some reason the very occurrence even a single tornado is somehow “unusual” and makes national headlines routinely, even if it hits nothing or does minor damage with no harm to anyone. When about 1250 tornadoes occur in the U.S. a year, a tornado is quite a typical event, not unusual.
Another item, this is the third year in a row where U.S. tornado fatalities have decreased. It is not just regression to the mean either due to the very high toll in 2011. In the last three years, the numbers have been 70, 55, and 46. This has more due to with random chance than climate, as we know all it takes is one badly placed intense tornado to make it a well above average year (i.e.
Joplin), but to level the playing field on an argumentative and prevailing public mindset level, a decrease is a decrease, and that is a good thing. Contrast if it went up 2012-2014, then the klaxons would probably be sounding and this would be utilized as “proof” the weather/climate is getting worse, even though as I said, this is random chance, either way! Mesoscale event placement is so far below mean large scale climate it is basically irrelevant to the issue. Another way of looking at it is that fatalities have resumed the typical in the last 3 years to what has been
occurring in most years going back to 1975.
Two main things at work here,
1) watches/warnings for tornadoes has improved considerably in the last 40 years, and
2) the number of people in this country has increased considerably, from about 216 million in 1975 to 316 million in 2014. So you have one item that decreases the risk of fatalities and one item increasing the risk of fatalities. You can crunch the numbers all you want here, but overall it at worst appears to be status quo in the long term mean.
One more item, although the number of total tornadoes per year is going up overall (and that is more a better detection/documentation fact than anything), the number of F3/EF3+ has shown a slight decrease in trend. These are the ones that do the most damage and cause the most fatalities, and what we should be most concerned with.
Bottom line there is reasonable evidence currently that tornadoes in this country both from a meteorological and fatality point of view are not getting worse. The U.S. represents only 6.6% of the land on the globe, but is the tornado capital of the world, and has a very extensive tornado database, so looking at tornado trends here is better than anything else we currently have to measure
overall activity.