Is There A Tornado Cycle?

I was just reflecting and considering the Hurricane Cycle that supposedly cycles every 20 to 30 years and is supposed to be associated with maximums and minimums in hurricane activity such as in the Atlantic. Last I heard we started a new cycle of increased activity back in 95 so we should see increased Hurricane activity in the Atlantic for some time.

My thoughts though are based around tornadoes. If hurricane activity and development is based on ocean temperature, African droughts, and various air circulations - basically weather makers then might not these same maximums and minimums create tornado activity cycles as well?

Guess I need to look up the details of exactly what these cycles are. Perhaps they only affect the Atlantic. If so then maybe it doesn't have as much affect on tornadoes because the Pacific probably plays a bigger role in west to east US weather than the Atlantic. However if both the Atlantic and Pacific are involved then I would think there could be a "tornado cycle". I wonder if anyone has ever looked at the historical data and trends and tried to determine this or tried to relate tornado activity and supercell production with hurricane cycle activity?

Edit:
Here's a link that discusses the hurricane cycle I found:
http://www.post-gazette.com/pg/04277/388989.stm
 
You can get somewhat of a long-term snapshot on Figure 1 in the following article of annual significant tornado days, and outbreaks:

http://www.spc.noaa.gov/publications/schne...do%20Outbreaks'

Because of the sharp inter-annual variability of tornado occurence, it is kind of a challenge to derive a cyclical pattern from this. Suppose you could construct some kind of exponential moving average line to attempt. The only observation I could feintly make out was perhaps a cyclical maximum from the mid 1950's to the late 1970's, declining since then based on lower highs and lower lows. Complicating this data, however, would be the secular increase on observational capacity over time - perhaps offset by improvements in structural integrity which may have made the "significant" threshhold higher over time since it is based on F-scale.

As for conjecture on what factors might explain any cyclicality, I suppose a starting point might be pattern shifts in the upper level jet - although factors which would, in turn, induce any such shifts would be beyond my pay grade to even attempt to guess at. Unlike hurricane patterns, which seem to be based more on "raw material" of the ocean and atmosphere, seems that tornadogensis is more related to a confluence of several specific factors. Notice there is no attempt each season for any professional forecast of tornado frequency, probably because there is no equivalent to something like the ACE index (ie - raw materials) used in seasonal hurricane forecasting.

Interesting speculation, but would be quite a challenge to establish data correlations, and even tougher to put forth causal explanations.
 
First and foremost, the right ingredients have to be in place to even intiate torndo-producing storms. If the circulation patterns are set up just right preventing any S/W troughs, abundant moisture, vertical wind fields, etc. from establishing themselves, then that can do it. This would be associated more with the long-term circulations and climatology. Of course, it all boils down to the fact that we don't really have long enough records of observations (not to mention how obs of tornadoes are skewed lately since reporting and spotting has improved) to really make any determinations.

Hurricanes are one thing. They are large enough and are drivien by few primary mechanisms. Tornadoes are such small-scale phenomena it may well be impossible to nail down all of the climatological variables.

First, we've got to figure out what exacty makes Storm-A produce a tornado when Storm-B doesn't even though they appear identical. This is why I will always be able to find a job somewhere.
 
First and foremost, the right ingredients have to be in place to even intiate torndo-producing storms. If the circulation patterns are set up just right preventing any S/W troughs, abundant moisture, vertical wind fields, etc. from establishing themselves, then that can do it. This would be associated more with the long-term circulations and climatology.

Yep... pretty much. The problem with tornadoes is their parent supercells are often a biproduct of the meso/microscale. Features such as outflow boundaries, cloud cover, etc. can't be determined by climatology.

Now consider how often we rate a season by big events. If just one or two significant events occur, many times, our whole perception of the season is changed. Well how many plains tornado outbreaks are governed by just the synoptic scale? I know I can think of a couple outbreaks/busts that were determined due to mesoscale features.

Aaron
 
There are some who believe tornado peak occurence coincides with an 11-year sunspot cycle. I've heard and read theories that both support and disallow this idea.
 
Originally posted by Aaron Kennedy
Yep... pretty much. The problem with tornadoes is their parent supercells are often a biproduct of the meso/microscale. Features such as outflow boundaries, cloud cover, etc. can't be determined by climatology.

Now consider how often we rate a season by big events. If just one or two significant events occur, many times, our whole perception of the season is changed. Well how many plains tornado outbreaks are governed by just the synoptic scale? I know I can think of a couple outbreaks/busts that were determined due to mesoscale features.
Aaron

I don't think I really agree. It's probably true that there can be exceptions, but I'd say on a whole that the synoptic and long wave pattern that sets up across the US combined with any blocking factors (which may affect high pressure placement), and jet placement are what set up the stage for the meso and micro scale to do their thing. Whereas it may be true that tornadoes are a smaller scale phenomenon primarily based in the meso and micro scale, I don't think these scales would play the role they do if the overall pattern wasn't strong. This is why things such as good SW flow are important. This is why I am thinking that seasonal or even longer range "decadal" tornado activity may be strongly influenced by the overall global patterns, wind flows, and moisture placement.

Imagine what the southern plains would be like if we continually throughout the year had sw flow, a strong upper jet overhead with good mid level flow as well bringing in low pressure short waves. With the Gulf opened up we'd be chasing constantly. One reason chasing down south has sucked for so many years lately is because the jet placement has gone north, and stayed north early on. That is synoptic scale.

Nice article listed by Mike Johnston by the way. Cool that it goes back so far, but it makes you wonder how reliable the data set is. Still it seems to show an increased period of tornadic activity starting about the 1920's, peaking between 1950 and 1970, and then on the decline to the present day. That seems kind of amazing because everyone always seems quick to jump on the bandwagon that global warming is causing increased tornadic activity with stronger tornadoes than in the past; however it appears that isn't true. From the '20's to 2005...that's like an 85 year cycle. It would be interesting if there was such a widespread cycle. Then again I am just now thinking too that any "cycle" may only be momentary as the Earth is in a constant state of flux. Things such as volcanic activity can affect the weather patterns and may interfere with the "cycle". Anyway...something to ponder.
 
Originally posted by Bill Tabor

I don't think I really agree.

I do. Storms don't care what the synoptic conditions are like - they only sense the immediate atmospheric conditions around them. If the local environment for the storm is favorable, it will thrive regardless of the larger scale actions. Synoptic patterns affect broad regional priming of the atmosphere, in either positive or negative ways. While you could probably tie synoptic pattern activity to global patterns, which do appear to have some influence from long period climate oscillations, numerous studies have attempted to find correlations and none have found anything substantial above the statistical noise level that I'm aware of.

Glen
 
Originally posted by Glen Romine
I do. Storms don't care what the synoptic conditions are like - they only sense the immediate atmospheric conditions around them. If the local environment for the storm is favorable, it will thrive regardless of the larger scale actions. Synoptic patterns affect broad regional priming of the atmosphere, in either positive or negative ways. While you could probably tie synoptic pattern activity to global patterns, which do appear to have some influence from long period climate oscillations, numerous studies have attempted to find correlations and none have found anything substantial above the statistical noise level that I'm aware of.
Glen

Just imagine the micro and meso scale without a synoptic pattern in place...there would be no background to set up and cause the meso / micro. All global weather is related as it is a closed system.
 
Originally posted by Bill Tabor

Just imagine the micro and meso scale without a synoptic pattern in place...there would be no background to set up and cause the meso / micro. All global weather is related as it is a closed system.

Energy in the atmopshere doesn't all flow down hill to the smallest scales from the the global pattern. When you walk outside and feel a gust of wind, that wasn't caused by a positive North Atlantic Oscillation index.

Glen
 
That arguement goes both ways... just imagine a synoptic setup without mesoscale processes occuring.

One example is the low level jet (a mesoscale process) which is often the primary transport mechanism for adequate moisture return off the gulf.

I'm not saying the synoptic pattern isn't important; it certainly is, but a tornadic cycle based off synoptic pattern will be much more noisy due to mesoscale events.

Aaron
 
My point is they are both related. Tornadoes aren't caused solely by synoptic or global scale, but they aren't created in a vacume on the meso / micro scale either. They are interrelated / and intertwined. It is the ultimate 'big' picture as the Sun is the ultimate weather maker on Earth which drives every other process. Because they are interrelated is why I wonder if there could be trends or long term cyclical patterns. Perhaps no one has determined what that cycle or pattern is, maybe the data set isn't big enough yet or no one has done that study yet. It may be there are enough negative feedback mechanisms to cancel any long term cycles. I'm not positive there is a cycle, but I don't think anyone is sure there isn't yet either though.

Anyway, I'll let this sit awhile and see what others opinions are.
 
Originally posted by Chris Nuttall
Hurricanes are one thing. They are large enough and are drivien by few primary mechanisms. Tornadoes are such small-scale phenomena it may well be impossible to nail down all of the climatological variables.

I totally think that any tornado cycle is a combination of synoptic and mesoscale setups/interactions. Like I said before though, our data set is just now large enough, nor do we fully understand all of the variables at play, to really make any kind of climatological determinations.

The mesoscale is often in such a dynamic flux that it is prone to quick changes and very difficult to observe.
 
The problem is that stats to help verify any kind of cycle are tainted due to the fact that many more tornados are spotted and reported now than 30 years ago due to chasers, spotters and technology. So even if there is a cycle we wouldnt be able to tell by the data available.

Are there more tornados than 30 years ago or just more people reporting them??? I say the latter.
 
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. While there are any number of contributing factors to offical tornado stats for any given year, it is a fact that some years (even recent years) go far above or far below the average (2002 and 2004 come to mind).

The fact that years can vary greatly from the average shows that storms are influenced by more than just the local environment, and would tend to support the idea that there is some kind of cycle. However, I don't see any evidence of an extended (20+ year) cycle, and I don't think we have enough accurate long-term data to be able to detect any long-term cycle yet.
 
The most compelling argument for a cycle is the fact that there are years (1988, 2002, etc.) when tornado activity is unusally low.

Well... statistics dictate that just because you have below/above average numbers of tornadoes in a year, you don't neccesarily have a cycle. It is possible to have the years spread out in a random distrubution.

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

p15.jpg


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