Tornado Forecasting: What's the next research priority?

[Jeff Miller]

The last few decades have been ripe with new understanding on tornadogenesis within supercell and non-supercellular storms alike. We have had an enormous amount of knowledge from such meteorological wizards as Chuck Doswell, Howie Bluestein, Josh Wurman, and many others. We've achieved the point of at least assessing rudementary knowledge about tornadogenesis within the "standard classical supercell" - that is - the supercell that is textbook and "according to definition".

With that said, we all know that there are infinite variables with tornadogenesis that science has not even scratched the surface with. We have tornadoes originating from Line Echo Wave Patterns. Non-supercellular tornadoes in front of bows and squalls. Landspout tornadoes. Waterspouts that make landfall over the southeast that can be quite damaging. Lowtop supercellular dynamics and structures, and the list goes on and on and on.

The question should be posed: With all the infinite possibilities we could research, what is our highest priority? Should we concentrate on supercell-meso tornadoes that are produced the "classic" way because they are the most damaging and highest possibility to become violent? Should we concentrate on linear/lewp/bow tornadoes because they are higher in frequency then violent supercell type tornadoes? And the big question - with all the possible infinite variables, how can we ever establish predictive forecasting with ALL types of tornadoes that is even close to becoming accurate if at all? What IS the next research priority, and is there anything on the horizon as far as a new "breakthrough" that mets are looking at that could possibly tie it all together as in a common denominator? Bottom line: What's next on the horizon with tornado forecasting in general?

And to pose on a personal level, what tornado riddle are you as a chaser looking most forward to seeing solved?

 

[Shane Adams]

I'd say the current priority seems to be confirming the actual tornadic wind speeds at ground level, as opposed to 50-100 feet from the ground. Recent studies have been trying to figure a % of "speed scrub" from the 100-foot level or so to the ground, whatever the lowest seeing range of the DOW radar is. I think a lot of what's come from this study had to do with the new F scale, and lowering the estimated wind speeds for each level.

So my short answer would be, research seems more focused lately on refining the F-scale damage parameters/wind speed estimates than it is the mystery of tornadogenesis.

 

[Skip Talbot]

Accurately forecasting tornado-genesis, regardless of the type and storm mode, seems like a daunting task not feasible in the near future. I think, however, that we are on the verge of a revolution in how tornadoes are understood and forecasted (at least in the short term). With the technological advances and dropping costs in wireless data transfer, we'll probably see much more detailed studies of tornadic cells as they can be sampled more thoroughly with perhaps a high resolution instrument array. More realistically, however, we should be able to create much more detailed computer models of supercells and tornadoes given the advances in computing power, especially in parallel processing. If we can create accurate models of tornado-genesis from various situations, and compare that it in realtime to high resolution data from a storm in progress, we may actually be able to issue accurate short term tornado forecasts for specific locations.

I agree with Shane though. Probably the most important area of research is studying the low level winds of a tornado. You'll probably get the most bang for your buck in this area of research, as the damage tornadoes cause is what makes them so important to understand. Tornadoes are going to happen and if we can apply detailed knowledge of the ground level vortex to structural engineering we may have better homes to take shelter in. This may ultimately save more lives than a few extra minutes and a more accurate tornado warning derived from cracking tornado-genesis.

 

[Ben Baranowski]

This is somewhat different than what is above, but I think just as relevant. (This was also mentioned on High Instability a few shows back). The discussion centered around the detection of signatures in radar data that preclude tornadogenesis. The sentiment I've been hearing of late is that any good indicator develops extremely quickly (within minutes). By the time these radar signatures are processed (either by computer of forecaster) the tornado can already be on the ground rendering them useless. So further study into tornado dynamics may become somewhat of an academic endeavor with little added knowledge to the forecast process (at least as the technology stands now).

 

[Mike Hollingshead]

What I've wondered lately is just how many buy into the horizontal rotational thingy. How the horizontal spin is tilted by the updraft. Seems like they talked on the show like it was fact. Maybe it is. I sure don't seem to buy into it though.

 

[Skip Talbot]

What I've wondered lately is just how many buy into the horizontal rotational thingy.

Mike, I've always wondered about that, but who am I to challenge the best minds in meteorology? If the tornadic vortex begins horizontally, why don't we see that reflected in the shape of the tornado? I can see the horizontal vortex being pulled vertically by the updraft, but wouldn't the base of the tornado still retain some of that horizontal component? The vortex is typically perpendicular with the ground. Perhaps someone here who understands the dynamics can explain it to the rest of us in layman's terms.

 

[Dan Robinson]

Like many of us I've spent sleepless nights trying to visualize in my brain the internal workings of what I've seen out in the field. My mind also has always had a hard time fully accepting the 'verticalization of horizontal vorticity' theory of tornadogenesis. I've heard this as being the mechanism for tornadogenesis, the mechanism for mesocyclogenesis, and/or both. As Skip points out, this theory is highly regarded by the experts so I'm not discounting it - but it seems a little counter-intuitive to me. I know you can't fully compare small-scale vorticies with large-scale ones, but when I see that all that a small body of water needs is a single-point drain to create a vortex - I wonder if the whole process is simpler than we've always made it out to be.

 

[Dave Gallaher]

What I've wondered lately is just how many buy into the horizontal rotational thingy. How the horizontal spin is tilted by the updraft.

I had managed to ignore this concept for the most part until my drive-by intercept on 3/1 this year. This storm was rotating at a speed I've witnessed when a funnel was going overhead, but it was totally horizontal, following the cell. The west side of the large rotation was going up and circling, exhibiting pointed-end cloud spikes that curled over the top. By extrapolation, if the trailing end of that axis had tilted toward the ground, it would have been a cyclonic funnel.

Back toward the topic, and perhaps out on a limb, I've always wondered what, if any, enviromental effects the passage of a tornado would cause. Could the combination of friction, mixing, centrifugal force, electrical discharge, moisture, collection and dispersion of particles from debris down to dust and beyond--and the sheer expenditure of a high degree of energy over a small area--be a catalyst for some currently unrecognized component of the atmosphere and/or soil?

Having said that, I have no idea of how data could be gathered for study, since the before/after aspects would require a clairvoyant knowlege of a tornado's path.

 

[Jeff Snyder]

Like many of us I've spent sleepless nights trying to visualize in my brain the internal workings of what I've seen out in the field. My mind also has always had a hard time fully accepting the 'verticalization of horizontal vorticity' theory of tornadogenesis. I've heard this as being the mechanism for tornadogenesis, the mechanism for mesocyclogenesis, and/or both. As Skip points out, this theory is highly regarded by the experts so I'm not discounting it - but it seems a little counter-intuitive to me. I know you can't fully compare small-scale vorticies with large-scale ones, but when I see that all that a small body of water needs is a single-point drain to create a vortex - I wonder if the whole process is simpler than we've always made it out to be.

The idea of vertical wind shear and streamwise vorticity giving rise to rotating updrafts has been relatively well researched for the past couple of decades. The tilting of horiztonal vorticity into the vertical and stretching of this vorticity by acceleration in the updraft can give rise to mesocyclone-scale rotation. In this regard, I'm not sure you'll find many meteorologists who will state otherwise. That said, for vortices of smaller scales, including tornadoes, dust devils, etc, the processes that can lead to their development are varying and not necessarily well understood (obviously). For example, tornadoes of the classic 'landspout' variety are caused by the vertical acceleration (stretching) of existing ambient vertical vorticity (often in the form of a misocyclone). As we all know, though, sub-storm-scale vortices (tornadoes, gustnadoes, etc) can develop in at least a few different ways. Some tornadoes and gustnadoes likely develop from strong lateral shear along gust fronts similar to the wrapping of a vortex sheet, and others are caused by very different processes. There was a really interesting seminar by David Lewellen of WVU that pertained to corner flow collapse as a possible mechanism of tornadogenesis and rapid intensification (the possibility of supersonic wind speeds was also briefly addressed). I only mention this because it's one example of a relatively recently-researched area of tornadoes. Lewellen is also one of a handful of folks running very high-resolution model simulations of tornado debris clouds and the effect of debris on tornado winds / flow structure. Quite interesting stuff!

Personally, I echo Shane's interest. We don't really know a whole lot about the lowest 5-10 m of tornadoes. It is in this area where probes and other in-situ observations become extremely important (the probes of Tim Samaras, the TIV / Sean Casey, sticknets from Weiss and Texas Tech, etc). I think we're a long ways away from local tornado forecasting along the lines of "a tornado will develop within 10 miles of intersection of AAA and BBB streets in 45 minutes". It's become increasing apparent that near-surface shear (0-1km, if not 0-500m) is a very important factor for tornadogenesis, so it would be interesting to get high-resolution low-level wind profiles near tornadic supercells (i.e. 0-3km winds at 10-50 m resolution). In a real-world sense, low-level wind profiles can very over short distances and short times, so there may be a more practical limit on what we can forecast (at least through the next 20 years). And what about low-level thermodynamic structure? Mobile radar observations have shown that "tornado-like" vortices may come within a couple 100 m of the surface without ever actually "touching down".

Hopefully we'll know more in a few years after VORTEX-II (2009-2010, most likely). The number of observations collected in the field will be entirely unprecedented (5-7 mobile radars, several aircraft, stick nets, probes, mobile mesonets, balloons, unmanned aircraft (maybe), etc), and it'll likely be our next "big chance" of gaining significant insight into how tornado development, sustenance, dissipation, failure mode, and so forth.

Paul Markowski has a brief overview of processes behind tornadoes that was given at the European Conference on Severe Storms... It's only 2 pages long, but it touches on several ideas. It can be read by following the link:
Tornadogenesis: Our current understanding, operational considerations, and questions
to guide future research (Paul Markowski)

 

[fplowman]

What I've wondered lately is just how many buy into the horizontal rotational thingy. How the horizontal spin is tilted by the updraft. Seems like they talked on the show like it was fact. Maybe it is. I sure don't seem to buy into it though.

Dr. David Gold spoke in great detail about this at the convention one year. I think it was the year before last.

When I say great detail it was hard to follow him without being a physicist that has worked on this project.

I did come away with this much though as you stated above.

Horizontal rotational axis winds come into play with the updraft forming rotational characteristics within a given storm that is affected ( rotating supercell ). This is a laymens understanding of his lecture of course.

Note: I am not a real meteorologist or physicist but I play one on TV. lol

 

[Paul Knightley]

I think the research has been skewed towards supercell tornadoes (for obvious reasons). What I think needs to be understood is whether fundamentally many tornadoes are created in the same manner, and that it's the larger-scale creation of the tornado-forming conditions which can come about in different ways. I was actually going to pose a question in a new thread today, but I think it will be perfectly at home here.

We know that tornadoes form in a number of different environments. For example, one may form under a rapidly growing cumulonimbus along a convergence zone whilst another develops under a mesocyclone. Many of these tornadoes "look" *fairly* similar - i.e. funnel shaped, rope shaped, or whatever, and most are *fairly* narrow. Now, I can kind of picture these as being the result of vertical vorticity being stretched from above - many tornadoes within mesocyclones are much smaller than the parent meso, and rotate about them. Perhaps these are all formed in a similar manner albeit under different conditions. Now (and this is where we approach the question I want to ask!) - occasionally a tornado assumes (by most other tornadoes) a fairly huge size (e.g. the Greensburg tornado), and my question is this:

Are these monster tornadoes actually the same kind of phenomenon as a "normal" tornado (including those which develop under mesocyclones and those which don't), or are they actually more akin to the whole mesocyclone itself being "on the ground" (for want of a better term!)?

I say "normal" because most tornadoes spawned beneath mesocyclones are nowhere near the size of the meso, but these monster storms could, perhaps, be closer to the size of the meso (although I understand that generally most mesos are larger).

It was seeing some of the footage from the May 3 OKC tornado, in which the tornado *seems* to be beneath a column of cloud, and as wide as this column of cloud which may me wonder whether these are formed in a totally different way to most other tornadoes.

 

[Nigel Bolton]

Tornado research will depend very much on where you live and to the type of convection that is typical within your area.

Here in the UK, it is well accepted that the supercell tornado is an extreme rarity, the T5(EF2) tornado that struck Birmingham on the 28th July (and forecast), was deemed to have been pendent from a supercell structure, as was the T4(EF1/2) tornado that struck Selsey on the evening of the 7th January 1998, tornadoes on this particular evening were forecast too.

However, most UK tornadoes are not formed from supercells or mesocyclones, and most actually form within cold air, or the boundary between two contrasting airmasses.

A lot of study has been undertaken into UK style tornadoes during the past 30, and particularly the last 5 to 10 years, and it has been deduced that there are a number of different tornado inducing mechanisms that occur within the UK, working either separately, or in conjunction with each other. It has to be stated, that normally several functions have to be working concurrently for a truly strong tornado to develop, but strong in the UK we are alluding to T4 and above.

These synoptic patterns can be listed as follows:;

1, Strong Ana cold front in association with a rapidly deepening area of low pressure. Can lead to ‘swarms’ of short lived, and generally weak tornadoes.

2, Zone of low level wind shear, especially near the south coast of the UK in winter. Can lead to the development of the occasional strong tornado, i.e. Selsey, if other factors are working concurrently.

3, Slack areas of low pressure in the late Spring or Summer, where the low circulation is filled with air that is cool, unstable, and very moist in depth. This set-up produces numerous photogenic funnel clouds with occasional short-lived weak touchdowns.

4, Vortex shedding by various land forms, including islands, ridges and coastal promontories. Can induce significant tornadogenesis if associated with other tornadogenetic factors.

5, Summer thunderstorm. Rare in the UK. The vertical wind-flow pattern in association with our severe thunderstorm generating synoptic situation is not conducive to tornado development in the UK, though it occasionally develops giant hail.

6, Point of Occlusion, or ‘Triple Point’ tornado. Rare, but can instigate singular, but potentially very strong tornadoes for the UK, namely T5 and above, these having marked longevity.

7, PVA feature in cool air in winter, strongly driven by upper trough. Occasional tornadoes can occur within a cluster of convection.

The area that does need more research in the UK, and in other areas of the world where the terrain is complex is the ‘Topographical Tornado’. There have been several instances in the past few years where low level vorticity has been generated by topographical land forms, and then ingested into a passing storm, the vorticity stretching to generate a tornado.

Nigel B.

P.S. I agree with Mike H, that I cannot visualise horizontal rotation being tilted into the vertical, though there is mathematical proof somewhere to suggest that this can happen. Having a mind that works conceptually as opposed to using maths, this is one model that to me makes no sense.

 

[Charles Kuster]

I echo what others have said in that understanding what is occurring in the lowest levels of a tornado is extremely important to understand. This could be our most effective way of saving lives through better construction. There is very little data in this area, but thanks to probes and the TIV we are gaining more knowledge in this area.

I would also be interested in the surface conditions (i.e. temp, dewpoint, wind speed and direction, pressure, etc.) all around supercells regardless of whether or not they produce a tornado. I think finding similarities in the RFD, FFD, or inflow portions of the storm could be valuable. How important is a warm RFD? How warm and moist should inflow air generally be? Were there any differences in the surface conditions between tornado producing supercells and non-producers? Projects like Vortex would help with this. I also think that the origin and evolution of the RFD could be important. Just my two cents.

 

[Paul Knightley]

Without a long Doppler dataset in the UK, it cannot be said with any certainty that supercells/mesocyclones are an extreme rarity - personally, I don't think they are.

As has been mentioned above, horizontal vorticity (HV) being tilted into the vertical is a fairly accepted view of the start of mesocyclone formation. However, I don't think it is especially applicable in tornado production, which is probably much more likely to be vertical vorticity being stretched.

An easy way to imagine HV is a rolling pin - now, if an updraught tilts that into the vertical, then you have vertical vorticity.