Guest essay by Alberto Z. Comendador
Temperatures in the USA have generally increased since the 1950s. Of course, anything that mostly increases over time will have a positive correlation with everything else that also increases; in the USA this includes tornado counts. And of course most correlations are utterly meaningless and devoid of causation. For a hilarious take on the issue, see spurious correlations.
The problem , as NOAA itself says, is that there is a bias: just because we observe more tornadoes than before, doesn’t mean their number has actually increased.
‘With increased National Doppler radar coverage, increasing population, and greater attention to tornado reporting, there has been an increase in the number of tornado reports over the past several decades. This can create a misleading appearance of an increasing trend in tornado frequency.’
They illustrate this by excluding the weakest tornadoes (the F-0 category), which is the one most affected by this observation bias. If one does so, there doesn’t seem to be a long-term increase.
From the NOAA Storm Prediction Center:
And if you look only at strong tornadoes, F3 and up, they’ve actually declined.
Today I want to look at the issue from another angle: changes in temperature. I have seldom seen this kind of analysis in climate and it seems to me temperature provides a good opportunity, because the yearly changes are so large compared to the long-term trend. By contrast, any observation bias has to be small. The population of states, coverage of Doppler radar, etc. are virtually identical from one year to the next.
NOAAs’ temperature data page shows this:
Temperature swings from one year to the next are sometimes in excess of 1ºC. In fact, that’s about as much as total warming since 1979.
Now, there are some aspects of climate for which yearly temperature swings are not very relevant; for instance, glacial melting depends mostly on the absolute temperature, not the change from the year before. Sea level rise depends both on water expansion (through heat accumulation) and additional water mass (through glacial melting). So it shouldn’t surprise us if we don’t see any correlation between temperature swings and sea level rise.
Still, I wanted to see if there’s something about tornadoes that makes them increase or decrease when temperatures go up. We’re always hearing about the 2ºC target, so I figure changes of over 1ºC should be enough to cause some change in the tornado count.
How I counted
NOAA’s storm database is here. As of this writing, at least the files for 2015 and 2016 have a new weird format that apparently removes the ‘event type’ column (and a lot of other things); I haven’t looked at all the files, for obvious reasons, but fortunately I downloaded the data a few months ago and those do indicate the event type (tornado, hail, etc).
So the files and R-Code I actually used are stored here. The link is only missing the data for 2016, which I got from Wikipedia. If anyone knows of a more ‘official’ answer I can plug it in – though honestly it wouldn’t change the results. In the Dropbox link you’ll also find my R-code and the temperatures for 1951-2016.
The 1951-2016 period has 66 years, but since we’re looking at changes, there are 65 ‘points’. And as you can guess looking at the chart…
…the correlation is 1.5%, which is to say effectively zero.
The problem with using changes in temperature is that, obviously, absolute temperature also plays a role. Perhaps going from 14ºC to 15ºC has no effect on tornadoes, but moving from 15ºC to 16ºC does cause an increase. To test this I checked only the years since 2000: an increase in temperature from that baseline leads to higher absolute values than one from earlier dates.
In that case the correlation is -33%. I don’t think this really means there is a negative relationship between tornadoes and temperature – it’s just that with so few points you will get skewed results.
What this doesn’t mean
This simply shows there is no correlation between tornado change and temperature change. Of course, in reality any change in temperature will affect tornadoes somehow; perhaps the changes that increase this count are offset by others that decrease it, or perhaps the influence of temperature is simply too small and gets lost in the noise of variability. To probe deeper, one could also look at trends depending on regional temperatures, or comparing day time with night time and so on.
For now that is beyond my means, in terms of both skill and free time. I hope you enjoyed this post – feel free to tinker with the data and code provided in the references.
References:
Tornado Climatology: https://www.ncdc.noaa.gov/climate-information/extreme-events/us-tornado-climatology/trends
NOAA/NCEI Storm event data: https://www1.ncdc.noaa.gov/pub/data/swdi/stormevents/csvfiles/
NOAA USA Temperature Data: https://www.ncdc.noaa.gov/cag/time-series/us/110/0/tavg/ytd/12/1951-2017?base_prd=true&firstbaseyear=1951&lastbaseyear=2016
Data files and R-code used to make counts: https://www.dropbox.com/sh/lb69l5isa25guc2/AAC4-gYr3N6TVDxEGzBB8fJVa?dl=0
R graphical language (free): https://www.r-project.org/
People think of heat as energy. Thus the warmer things are, the more energetic the system.
Not quite. The ability to do work, which drives weather systems, is not a function of temperature but of temperature gradient — that is, of spatial differences in temperature.
Thus one should not immediately assume the rising temperatures produces more energetic weather systems.
And that’s partly due to the fact that the thermodynamic temperature is the geometric mean of a defined sample of matter’s internal kinetic energy *and* nothing else. The thermodynamic temperature, by itself, tells you next to nothing without the other relevant information, other than the constituents of the sample at the higher one are generally moving faster than they are at a lower thermodynamic temperature. The temperature tells you a little bit about the total energy within the sample.
So why do most tornadoes occur in the US? Why doesn’t the rest of the world get some of this action?
I can’t see temperatures causing these things less or more when they occur over a wide temperature band.
Well if you know nothing of what causes them, that is not a very surprising result.
“So why do most tornadoes occur in the US? Why doesn’t the rest of the world get some of this action?”
I think it is a matter of topography.
The U.S. is a big, wide area, and a lot of moisture available to certain parts of it during the spring and fall.
A strong cold front comes into the northwest U.S., and causes a lot of rain but few if any tornadoes because the temperature differential isn’t large enough in that area. As the cold front passes through Arizona and New Mexico there is a bigger heat differential but still no tornadoes because there is no moisture to work with. Then as the cold front passes over the Rocky Mountains and enters the Great Plains, it starts running into warm, moist air, and the warmer moist air is usually located in Texas, Oklahoma, Arkansas, Kansas, Missouri, and Nebraska as the cold front pumps moisture and warm air up from the Gulf as part of the process. And all these forces meet right in Tornado Alley. As the season gets closer to summer the focus of tornado activity moves east from Tornado Alley, because there is usually a big high pressure system forming over the center of the nation. Then the heat of summer sets in and that’s the end of tornadoes until the heat breaks.
Very well put. You should take over for B Nye, last I heard him speaking about this very question he mangled it all to hell.
We have a potential tornado maker of a weather front coming into Tornado Alley now, although, right now, it looks like the storm fronts are pushing south to north along the front, which means they won’t have as much potential for big tornadoes. If the Storm Fronts were moving from southwest to northeast along the weather front (the jet stream), then the potential for large tornadoes is much greater. The angle the jet stream takes makes a lot of difference in the strength of these storms.
The wind has been blowing fairly hard here for the last two days, but not as hard as the weather front that went through here a couple of weeks ago which clobbered the east and northeast U.S. Those winds were “howling”. Not so much this time.
Here’s the weather radar map I use:
http://content.wdtinc.com/clients/koln/map2.php?MAPID=14116
B Nye seems to mangle all things science. Bill is very confused.
When my son was young he watched the early B Nye videos for kids, they were OK, then he expanded into AGW advocacy and you could really see the difference. Still have a couple of VHS tapes of his elementary school type shows, stuck to basic science at kid level, fun experiments and such. Then BANG, loony tune time. Makes me wonder what, medically, happened? Early onset Alzheimer’s? Traumatic brain injury? Some sort of chemical imbalance? Something happened.
And thanks for that active weather map link! Put it right below AccuWeather in my book marks.
BTW thanks to Sr. Comendador for archiving and sharing this data. We were warned that data would start disappearing when Trump was elected.
I pointed out that it would not be Trump which was behind but the alarmist, activist scientists.
What is the direction of the “rotational spin”, …… clockwise or counterclockwise, …. of a tornado and a “dust devil”?
Are they the same or opposite?
Is the “rotational spin” reversed for tornadoes or “dust devils” that form in the Southern Hemisphere?
The tornadoes that I’ve seen rotate counterclockwise, but could rotate either way, depending on local conditions. Dust devils definitely may be seen rotating either clockwise or counterclockwise; but once a rotation direction is established, it maintains it until it dissipates.
Thanks for your response, cd, …… I was curious if there was a specific rotational direction because I had never researched it or ever heard/read anyone say anything about it,
Anyway, I was just wondering if their rotational direction was in any way related to or determined by the N/S hemisphere in which they formed, …… like the rotational direction of water flowing down a drain.
I don’t think that there is a preferred direction, either, for drains. I’ve seen them rotate either way. I’m in the Southeastern US of A. I would say that, since there isn’t enough of a differential in the local Coriolis force for such small areas, that it is the local factors that give the initial direction. For large circulations, such as hurricanes/cyclones or mid-latitude baroclinic systems, which span 500 to 1000 miles, there would be enough of a differential in the northern and southern ends to make them have a preferred rotation dependent on the bulk pressure differential. So high pressure areas have winds that change direction in a clockwise fashion and low pressure systems have the inverse direction.
[youtube https://www.youtube.com/watch?v=_xCssYxvcsY&w=560&h=315%5D