Is There A Tornado Cycle?

[Glen Romine]

Originally posted by Bryce Stone
The most compelling argument for a cycle is the fact that there are years (1988, 2002, etc.) when tornado activity is unusally low. There are also years when the numbers are very high.

This itself isn't evidence of a cycle, but variability. It is easy to confuse climatology with giving what the "normal" number of something should be. For instance, the climatological high temperature might be 92 degrees for today somewhere, so maybe you would expect the high to be 92 - anything else suggesting some abnormal weather pattern ongoing. But the actual high is no more likely to be 92 as any other value within a given range of expected values. Same thing with tornadoes - except the data fed in the statistics are of far poorer quality than that of temperature, so the range of normality is less defined. Only once the range of typical variability from year to year is established, and some would argue it is far from there yet, then we can attempt to ascertain whether one year's high or low count is within or outside of the range of expected values, indicative of some 'external' forcing. Otherwise, you could probably just make any correlation you want - such as a tornado drought is more likely when a republican is president.

Glen

 

[Mike Johnston]

Glen wrote:

It is easy to confuse climatology with giving what the \"normal\" number of something should be.

Yes, we've been through this confusion over the term "normal" a few times before on the board, but once again here is a link to an excellent article by C. Doswell on the subject:

http://www.cimms.ou.edu/~doswell/Normals/normal.html

 

[Bryce Stone]

Oops. Obviously I didn't know what I was talking about. I read the entire article, and found it quite enlightening. Thank you.

So after reading his essay, I can't help but wonder how we can say for sure that there even is a hurricane cycle. The researchers in the article seem to be going off only about 100 years of data collection. Not to hijack the thread, but is the idea of a hurricane cycle widely accepted in the scientific community?

 

[Bill Tabor]

Still not sure if you folks are totally getting what I am trying to describe. Maybe you are to some degree. I'm not saying that the synoptic or global scale is causing the tornadoes. As Glen and Aaron stated the creation of supercells, and tornadoes is usually governed on the meso/mico scales including possible local features such as cap rock, outflow boundaries, shortwaves, meso lows, etc. But what I am saying is the difference between a record year of tornadoes and a tornado drought may be the position of the jets, the type and location of flow, etc. These factors may (and should) be related in a global sense (like in hurricane forecasting to some degree) to what I believe are "weather makers" or at least weather creating variables such as ocean temperatures, surface glaciation, ocean current flow patterns, etc. Since the synoptic longwave pattern to some degree dictates where shortwaves will pass within the flow then, if these global / synoptic features are altered from year to year, or decade to decade, or even century to century then for periods of time I would think that would affect things like the number of tornadoes that occur in the US in a period of time, along with the geographic distribution of those events. Not sure if it would affect strength but it is possible. Now, what I am not sure of is if these year to year differences would show up as 'cycles' in time. Perhaps other things in the year to year tornado cycle affect these fluctuations and make it difficult to tell. Certainly no study has determined this yet, but we have to remember that science is still going forward and tomorrow may find something new.

An example of what I am talking about perhaps would be why is Texas not the prolific tornado producer it once was? I think there is big reporting in Tx keeping the number of tornadoes up, and probably a lot of false positives, but I think most chasers agree that Tx and probably even Tx & Ok for the most part are not as good to chase as they used to be say ~ 10 to 30 years ago. (To some degree this was a little better this year though IMO (as I had a good year :lol: ).) For over 5 or 6 years chasers have been regularly going to SD, MN, IA, etc to chase tornadoes and sometimes even in the early season when you'd expect tornadoes in TX and OK. This has to do with jet placement, location of ridges, blocking, and flow overall in order to create a totally separate geographic distribution.

Maybe what's really happening is there is a cycle but it is only a year to year cycle. Still this doesn't explain why north has been better during summer over periods of years then it used to be. Then again, that can be part of it too. The chart we were looking at earlier was overall total US tornadoes, and not US tornadoes by region. Perhaps any cycle longer than a year affects regional numbers and not US wide tornado counts which may remain about the same. This shift to the northern areas is also curious as for if that has not occurred in the past then maybe it is some latent sign of meteorological effects of global warming (assuming nothing else explains it) whether man made or not.

To my knowledge of course right now this is only speculation. Until a study finds some linkage or cycle then there is not much to discuss. However this might make a great paper, or study for you met students in school. I guess the biggest problem we have though is the length of time data has been collected, along with the quality of that data. Early on there weren't many resources to report or observe severe weather with and not many people were knowledgeable, combined with a smaller population and geographic distribution of people in the US. Today, although we have the tools, and people some think this leads to over reporting. I think it would be tough to reconcile these issues but maybe it can be done to some degree. Someone would have to study and learn of the approximate accuracy of these numbers in some way.

 

[Bill Tabor]

As for cycle versus variability I would think in the most straightfoward definition variability is an observance of values without a reason and possibly recording them. A cycle on the other hand is something that has been studied, and identified about a set regarding repetition. A statistical pattern set can vary and that doesn't necessarily mean a cycle without further data, but it is also true that the variance can and may be caused by a cycle of values, or some relationship. This cycle then would lead to the observance of variance.

So whereas temperatures or tornado values may vary, and not necessarily due to a cycle, this does not exclude the possibility that a cycle is taking place.

 

[Bill Tabor]

Ok continuing along here...sorry three posts in a row - LOL! After reading all the thread over again and Doswells paper on weather and normality here are my comments:

Basically I think it is still plausible (theoretically) there could be such a thing as cycles for tornado activity, and this may not just be random variability about a distribution; however the data set may be questionable as to quality over the years being studied, and there may not be enough of a data set (in years) to yet determine a cycle either for the entire US or regionally unless the cycle only repeated every few years or so. Probably the data set would also be too small to tell if it was truly a regular cycle repeating "many" times or just a recently manifested cycle as well.

Perhaps if it was broken down regionally some repetition could be noted. I think it was tough to tell any pattern necessarily from the entire US study.

 

[Mike Johnston]

Bill, yes, I see your point regarding broad synoptic patterns influencing, or, we may even go so far as to say, determining, overall tornado activity for a given area. From looking at the data that is available, as limited and subject to flaw as it is, it just seems like the inter-annual variability is so great that it is difficult to derive any conclusion about long-term cyclical patterns. Now, just because there is great inter-annual variability does not necessarily mean that such variability is due to random factors. I think common sense tells us that long wave patterns during the climatological tornado season is of supreme importance to tornadic activity. So, it seems before we can reach any conclusions on long-term cyclicality, the first step is development of a methodology to forecast tornado activity for a given season. Why isn't this being done? Well, I'm not certain, but I would speculate that the tornado is still viewed, historically, as such a random and localized event, that it might be difficult to justify a social expenditure in pursuit of such information. However, if you think about it deeper, I'm not so convinced that it wouldn't be worthwhile. After all, you're basically talking about a 3-month long-term forecast. Seems to me that existing resources within NSSL and SPC could be effectively leveraged, with perhaps only modest incremental expenditure. The social benefits? Well, if a particular geographic area is highlighted for a probability of greater than average tornadic activity for a season, emergency preparedness and public safety awareness initiatives would be heightened. True, perhaps harder to justify as solidly as a seasonal hurricane forecast, but just might have some merit nontheless.

Hopefully, this topic will generate some more discussion. If nothing else, it's fascinating to consider.

 

[Sarah Berling]

That's a really interesting idea, Bill. I hadn't considered it before...but I'm inclined to agree with Aaron, that tornado formation is a bit random. They're just too small for there to be a cycle, I think, sort of the same way they're too small for the coreolis effect to really affect them. (The correllation makes sense in my mind, at least.) Just my two cents, for what they're worth...

Sarah

 

[Bill Tabor]

Here's how Mr. T. and "Chuck" see it:

See some of Mr. T.'s chase school:
http://www.stormtrack.org/humor/mrt

 

[Jason McIntosh]

I feel that tornadoes are random. Just because you have all the ingrediants doesn't guarantee a tornado outbreak. I also feel that active years and not so active years are random. Weather itself is random. Thats the beauty of it all. It would also be hard to prove the theory of a cycle because of the advancement in tornado forcasting over the past 50 years. 200 years ago there may have been 3,000 or more tornadoes in a year. We didn't have the resources or technology to record tornadoes back then. :roll:

 

[Mark Farnik]

I've also been pondering the existence of a tornado cycle, and reading this thread has given me great insight into the many possible factors that would influence such a cycle. Bill, your speculation on the reason for the significant shift of tornadic activity to more northern areas of the Great Plains is very interesting and warrants further discussion/study. Unfortunatley, even with the majority of tornadic activity shifting north, Colorado has seen no significant increase in tornadic activity. If anything, the last couple years (aside from May 10 2004) tornadic activity in the Centennial State has gone down . There are a couple of reasons I think we don't get nearly as many tornadoes as our neighbors a hundred miles to the east in western Kansas or Nebraska do. One of them is that we are so close to the mountains that any front approaching from the west is torn apart. Further east the fronts coming from the north have room to turn southeast/east. Also, the dryline tends to form in very far eastern Colorado on days when we have the potential for tornadic storms and then move east into western Kansas by early afternoon, triggering all the action out there. Also, the infamous lee side lows tend to form over us and then strengthen as they move east, leaving us with a thick stratus deck and spawning tornadic supercells in north central KS/south central NE. Only rarely (May 17 2000) do we get a strong lee side low producing multiple tornadic storms over the northeastern plains of Colorado. Also, our high elevation and semi-arid air makes it much harder for decent moisture to advect from the east. About the highest dewpoints we ever get are near 60 degrees; the really juicy 60/70 TD's never make it past the KS/NE border. It is almost impossible for the jet stream to be oriented favorably for tornadic storms out here in the far western High Plains. Being less than a hundred miles from the Rocky Mountains really screws up the tornadic potential of the local storms. :evil:
Sorry about getting off topic, but I thought it was interesting that while Kansas/Nebraska/Iowa/North and South Dakota have seen the number of tornadoes annually and the frequency of outbreaks increase, Colorado has been left out of the action.

 

[Bill Tabor]

Sorry about getting off topic, but I thought it was interesting that while Kansas/Nebraska/Iowa/North and South Dakota have seen the number of tornadoes annually and the frequency of outbreaks increase, Colorado has been left out of the action.

Well, as I recall Colorado has been in a bit of a drought for a number of years. That could be a symptom too.

 

[Kevin Bowman]

more hurricanes mean more tornadoes a lot of the time, i know this is common sense

 

[Mark Farnik]

Yeah, Bill, Colorado has been in the grips of an especially severe drought off and on since 2000. 2002 was the worst, but we are yet to see any consistently normal/above normal precip for more than a month or two at a time. The drought has also caused us to lose or have very low yields on many of our crops (my father is a farmer) and has left us some $70,000 + in debt. It's very very depressing. The drought has forced a lot of the smaller farmers in the area to pack up and leave. My dad is about the only 1000 acres or less farmer left in the county (we have a grand total of 800 acres; whoop de doo, as they say. To make a profit farming where I live and justify the expenses of farm equipment, seed and chemical purposes, you need 1500 acres or more. My dad has no money to buy land, so we have no chance of ever making money off of our farm. He's looking for a job right now. The drought has killed his dream of farming, as well as passing it on to me; I'm going for an English/Journalism major. I'm staying out of agriculture. My dad is the third generation of our family to farm on our homestead, and sadly it will be the last generation.

 

[Bill Tabor]

Yeah, Bill, Colorado has been in the grips of an especially severe drought off and on since 2000. 2002 was the worst, but we are yet to see any consistently normal/above normal precip for more than a month or two at a time. The drought has also caused us to lose or have very low yields on many of our crops (my father is a farmer) and has left us some $70,000 + in debt. It's very very depressing. The drought has forced a lot of the smaller farmers in the area to pack up and leave. My dad is about the only 1000 acres or less farmer left in the county (we have a grand total of 800 acres; whoop de doo, as they say. To make a profit farming where I live and justify the expenses of farm equipment, seed and chemical purposes, you need 1500 acres or more. My dad has no money to buy land, so we have no chance of ever making money off of our farm. He's looking for a job right now. The drought has killed his dream of farming, as well as passing it on to me; I'm going for an English/Journalism major. I'm staying out of agriculture. My dad is the third generation of our family to farm on our homestead, and sadly it will be the last generation.

Wow man that sucks. Sorry to hear about it. The other day I was watching Megaweather or something like that and it was on El Nino. It was a 2005 production I believe. Anyway it talked about El Nino and how it causes such devasting crop failure, drought, disease, flooding in all these places. They discussed something called a Mega El Nino that doesn't happen very often but may last up to 100 years at a time. Apparently there was some great civilization in western South America I believe that was thriving until one day they were just gone. They theorize it was a Mega El Nino that wiped them out.

I'm not suggesting that what happened with Colorado was El Nino the tornado cycle is, but was just thinking of the parallels of how weather gone bad can affect us and how any of these cycles can occur at any time.