What's wrong with Indices and Parameters?

Doswell just goes to remind all of us that a good forecaster needs to look at all the available data, and not just stick to one or two particular model solutions or parameters, since they all are parts of the puzzle. This is where situational awareness and experience are critical in determining which ones are right and wrong in painting a true picture of a given situation.

Damon Poole
 
Usually I agree with Doswell but in this instance I think he's basically attacking a straw man. Doswell's main complaint concerns some of the products available at the SPC mesoanalysis page. He claims that various indices and parameters (e.g. CAPE) have no real predictive value in forecasting, or at least none that has been rigorously demonstrated. Which is all fine and good, except that as I understand it forecasting is not really the purpose of the mesoanalysis page. The page is a good one-stop site for getting a good idea of the current state of the atmosphere - nothing more, nothing less. It is not really intended as a forecasting tool - it is after all clearly labeled as an "analysis page". It's true that many of us use that page in making last minute forecasts, and perhaps Doswell's essay can be read as a cautionary tale about doing precisely that, but the fact remains that not many people look at the page until after all forecasts have been made and the chase is on. In short, the various indices and parameters may indeed have no predictive value, but so what? That's not what they are really intended for.

Edit: this post more or less retracted, see new post below.
 
I think the problem with the SPC Mesoanalysis page is that it has consistently over-analyzed CAPE which eliminates CINH, etc. I mean, right now, there's supposedly 2500 j/kg of CAPE in C. MS, but the 21z sounding from JAN has 900 j/kg. That doesn't help you analyze the weather, let alone forecast.

Gabe

EDIT: Must mention that is not a knock on the SPC...they do a fine job.
 
Actually, upon reflection and a careful rereading of the essay, I kind of retract what I just said in my post. I think I now understand what he’s saying. Basically it boils down to the fact that the numbers on the mesoanalysis page (and elsewhere) may not always reflect reality, at least not in a way that’s useful to the forecaster. There undoubtably are situations in which the indices become downright misleading, and so they should be taken with a grain of salt.

Still, I’m not about to stop using the SPC SigTor and Supercell indexes, let alone CAPE. We have to use the tools that we have, flawed as they may be. But I agree that the mesoanalysis page can sometimes paint a picture that seems to bear little resemblance to reality. What can you do, you just have to keep on top of things and pay close attention to the actual observations on the ground, and not rely completely on the indexes.


Edit: just to clarify, I'm not trying to knock the SPC in any way either. The analysis page is a fabulous tool, one that I use regularly.
 
That's exactly the point, Dave. Use all the tools, but always keep the big picture in mind. Especially when forecasting, spotting, or chasing. I also agree with you, I won't stop using the SPC Analysis Page, or any other data I can get my hands on. To do so would be rediculous.

Damon Poole
 
Doswell just goes to remind all of us that a good forecaster needs to look at all the available data, and not just stick to one or two particular model solutions or parameters, since they all are parts of the puzzle. This is where situational awareness and experience are critical in determining which ones are right and wrong in painting a true picture of a given situation.

Damon Poole
[/b]

I agree. I enjoy Doswell's essays immensely, but this one is a little unnecessary, unless the intended audience is merely newbies or the severely inexperienced. There really isn't anything earth-shattering here.
 
I think the problem with the SPC Mesoanalysis page is that it has consistently over-analyzed CAPE which eliminates CINH, etc. I mean, right now, there's supposedly 2500 j/kg of CAPE in C. MS, but the 21z sounding from JAN has 900 j/kg. That doesn't help you analyze the weather, let alone forecast.[/b]

I think you're on the mark Gabe. I completely understand why Dr. Doswell posted the essay, because I hear many, many chasers (some quite experienced) say things like, "I don't understand why there were no big tornadoes, because the 18Z RUC showed 30 kts of 0-1 km shear" or "Why didn't the cap break - the SPC mesoanalysis page showed 0 CIN for hours". It's not just models; it extends to radar: "The radar algorithm is showing 3.2 inch hail, up from 3.1 inches in the last volume scan".

This doesn't necessarily mean anything is wrong with the parameters themselves, but the problem is the use of them. I saw a (generally) very good WFO last week getting all worked up about very large low level shear parameters issuing lots of tornado warnings, but completely missing the fact that dewpoint depressions were large, confirmed initially by observed high cloud bases and later by the generation of lots of cold outflow. Yet the tornado warnings kept coming. In this case the 0-1 and 0-3 shear numbers were indeed large as confirmed by every observational data set, but it was not important to tornado potential when every high-based updraft was quickly being undercut by cold outflow.
 
I think the problem with the SPC Mesoanalysis page is that it has consistently over-analyzed CAPE which eliminates CINH, etc. I mean, right now, there's supposedly 2500 j/kg of CAPE in C. MS, but the 21z sounding from JAN has 900 j/kg. That doesn't help you analyze the weather, let alone forecast.

Gabe

EDIT: Must mention that is not a knock on the SPC...they do a fine job.
[/b]

Gabe,

I don't understand where you saw such a discrepancy:

The JAN 21Z sounding - sbCAPE = 1711 J/kg, mlCAPE = 1268 J/kg
http://www.spc.noaa.gov/exper/soundings/06040721_OBS/

The 21z mesoanalysis showed values in the proper range for the area near JAN, without the benefit of that sounding:
http://www.spc.noaa.gov/exper/ma_archive/

The criticisms of the mesoanalysis page are valid *if* you don't bother to learn how the values are calculated and you have no idea when it may be unrepresentative. If it were perfect, we probably wouldn't be having this conversation because there would be no SPC meteorologists!

Rich T.
 
I think the problem with the SPC Mesoanalysis page is that it has consistently over-analyzed CAPE which eliminates CINH, etc. I mean, right now, there's supposedly 2500 j/kg of CAPE in C. MS, but the 21z sounding from JAN has 900 j/kg. That doesn't help you analyze the weather, let alone forecast.

Gabe

EDIT: Must mention that is not a knock on the SPC...they do a fine job.
[/b]

As Rich points out it's just a difference of how they calculate CAPE. The SPC Soundings and Mesoanaylsis uses VTC (also developed by Doswel I believe) which takes into effect moisture/density for what most consider a better presentation of avaliable instability. Parameters, algorithims, et cetera, is just an adjunct to the more raw data, allowing a forecaster to see all which is at hand. There is only a certain amount of time avaliable in the decision making process and only a certain amount of data one can look at. If there are ways to highlight particular threats/particular areas then I don't see that as a dis-advantage. The impression I got from the paper is that forecasters are going to look less at heights, surface anaylsis, etc. Because of a growing reliance on parameters, but I don't think this is the case or will be the case.
 
Gabe,

I don't understand where you saw such a discrepancy:

The JAN 21Z sounding - sbCAPE = 1711 J/kg, mlCAPE = 1268 J/kg
http://www.spc.noaa.gov/exper/soundings/06040721_OBS/

The 21z mesoanalysis showed values in the proper range for the area near JAN, without the benefit of that sounding:
http://www.spc.noaa.gov/exper/ma_archive/

The criticisms of the mesoanalysis page are valid *if* you don't bother to learn how the values are calculated and you have no idea when it may be unrepresentative. If it were perfect, we probably wouldn't be having this conversation because there would be no SPC meteorologists!

Rich T.
[/b]

I think that might have been, as Scott mentioned, a difference in how CAPE is calculated. IIRC, the sounding which I saw with 900 j/kg of CAPE was on the COD website, which probably calculates CAPE a bit differently. In my observation, CAPE on the COD sounding page tends to be a bit less than most analyses whereas I've noticed somewhat of a high bias from the SPC mesoanalysis. There are a number of times where I've seen CINH at 0 j/kg and a convergence max in the same area, and no surface-based convection fired (e.g. 5/22/05 in N OK). Nearby soundings showed a much more stout cap than what was advertised on the mesoanalysis page.

Please don't take this as a knock on the SPC, I'm just calling as I see it (though I may be wrong). I find the page to be quite helpful otherwise (especially the kinematic parameters).

Gabe
 
The SPC runs a 2-pass Barnes surface objective analysis around :05 after each hour, using the latest RUC forecast as a first guess. Next, the surface data is merged with the latest RUC forecast upper-air data to represent a 3-dimensional current objective analysis. Finally, each gridpoint is post-processed with a sounding analysis rountine called NSHARP to calculate many technical fields related to severe storms. [/b]

The SPC meso page is essentially massaged RUC model output. Take the current surface obs and throw them in with the model UA data to make some forecast soundings. Sounds great but the longer you are from the 12 and 00z sounding data the larger the error in the UA data... making those 15 and 18z soundings all the more precious.
 
I haven't read the Doswell article yet, but read Doswell all the time so I know what general slant he has. I hear the same stuff from other older more experienced, traditional forecasters as well. I hear that a lot of the tornado parameters and stuff are junk and you can't rely on them - same old song.

I love the SPC Mesoanalysis page. Had I listened to it a couple of years ago in KS and seen the values of 60 near Mulvane for Craven Sig Svr I might have scored a daylight tube. Having said all that I am a fairly non-traditional forecaster and just do it all in my head. I don't rely directly on any parameters or indices, but first review the current state of the atmosphere, surface, upper air, review different models along with their parameters, and forecast soundings. Once I've looked at all this I then scan many of the parameters and masks you see on Earls page. It's hard to say how I come up with a forecast solution. Basically I look at and try and remember commonality and differences between them all such as an area of common interest and then I may look at stuff such as Jon Davies Tornado mask or Rich Thompson's Sig Tor, supercell composite, craven. Of course these are forecast versions on Earls page. The mesoscale analysis is much closer to real time and reality. Sometimes I decide some of that stuff on Earls page is a lie. Some of those will tell you that there is wide spread risk, but reality is there is risk but only in places where the right conditions exist such as along boundaries. (I think modeling boundaries / boundary implications is the next frontier in forecasting). Anyway, based on what I see some of it I throw out and some I keep, and that changes with each model run.

As for SPC Mesoanalysis though in particular the tool is VERY good. Ignore it at your own peril haha and I will use it to get torns at will. If you do your homework and you do a good forecast and then you have the Mesoanalysis tool to alert you to rapidly changing conditions and where potential tornadoes may develop then you may be there when they form. I know because I do this all the time. This tool on more than one occasion has helped me immensely to be just that much more timely to pinpoint a chase target. It may be that it overestimates cape a bit just like the RUC, but that may actually be a more accurate reflection of cape than many other sources. Another good one of instability is Goes Quantitative Products.

I'll read the article, but I doubt it will change my mind.
 
Conclusion
In my experience, many forecasters, implicitly or not, are seeking a "magic bullet" when they offer up yet another combined variable or index for consideration. If forecasting were so simple as to be capable of being done effectively using some single variable or combination of variables, then the need for human forecasters effectively vanishes. If I or anyone else can produce such a thing, the day of human forecasters is over. There may be other reasons for the demise of human forecasters, but it seems unlikely to me that weather forecasting can be so easily distilled into an all-encompassing variable. A forecaster seeking to find such a variable is not only unlikely to be successful, but if success were achieved, s/he would be out of a job!

[/b]

I quote Doswell all the time, but I think he is off here. Sure forecasters and weather scientists want a 'magic bullet'. That's part of progress and the desire to improve tech, the background science, and take fundamentals (such as values seen on sounding and hodographs), and provide multiple different ways of looking at the atmosphere to quickly and effectively provide insight into what is currently, or will soon take place in the atmosphere. True they aren't there yet, but some day they may be. I wouldn't be so quick do blow off all the tech as that is the business he is in. Yeah it may put people out of work. That happens all the time and is just part of the upheaval we see in the modern computer age. I sure hope that all the folks like Rich T don't stop pushing the envelope just because they are afraid of job security. Think of all the times in the past when a person or group said something couldn't be done, or something shouldn't be done. They said that the Earth was flat, they said man would never go to the moon, no one could fathom atomic power. True the Earth and it's forces are complex and are ruled by uncertainty, but I woudn't bet against man's future ability to understand and predict weather. Sure you shouldn't just look at one stupid parameter and believe it to be God's truth. But no real meterologist is going to do that without a forecast first (as many of you have stated). Did any of you look at Mesoanalysis the other day when torns were blasting TN? I did and it's parameters were off the chart!
 
Ok, I've read the whole article. Interesting. I don't think he is entirely down on the SPC or Mesoscale Analysis tools, but I suppose wants everyone to keep perspective on what they represent. I agree they aren't necessarily 'forecasting' tools as any value in that regard needs to be proven experimentally. However I do believe they are reasonably good diagnostic tools. True some have limitations and it is up to us to know what they are. I think their true value though is in the diagnostic realm after a forecast is made and visually assessing the progress of that forecast. As stated, and with regard to sparseness of data sampling input and errors with modeling, etc there will always be assumptions made that may not always be 100% correct. The quality of the diagnostic likely will vary based on the particular scenario and the particular diagnostic. Often I tend to monitor trends with them. For instance temp, dewpoint, moisture advection increasing and moving to a particular spot or direction. Growth and concentration of STP, SCP, Sig Svr, EHI, convergence and lack of Cinh at a particular location. I agree that experimentally verifying their accuracy is a good idea. Perhaps this could be done automatically using a large database of historical data including tornado reports and just running the data through it retroactively. There are similar analysis systems for stock trading that go backward in time and compare a statistic, method, or variable for it's utility in predicting future stock price based on results.

I don't quite agree with him on combined variables / indices. The weather scientist in him is forcing him to think that if they don't directly relate to proven physical principles or processes then they are of no value. To some degree this can be true if you are trying to have them accurate in 100% cases. Take for example CAPE. Now perhaps it isn't proven that it is real or reliable. Sure tornadoes can happen with low or maybe even no CAPE, but does that mean that it is worthless? Far from it IMO. We know that in most tornadic cases CAPE is a usuable value as a future indicator of potential problems. I hear the same thing about EHI all the time, but I love that statistic and a most of the time it works fairly well as a rough guide to where you could have severe. Notice I said COULD and not WILL. Anyway I think you can combine different statistics and create something useful. A simple tornado parameter to help diagnose a large percentage of tornadoes would be to just take indice values that historically have been maximized in areas of tornadic outbreaks and combine them in a rational way that makes sense. These might take into account cape, lifted indices, shear at various levels, moisture, cinh, etc. It's tough to have one of these catch all tornado scenarios, but if it starts reading very high numbers you might want to check out why? Hmm, I'd kind of like to try my own hand one day at trying to build my own parameter. Hopefully the idea is with any of these parameters and combined indices that met scientists will continue to research and study and refine what these parameters do, and how good of a job they do at diagnosing or forecasting severe weather. Perhaps you need different tornado indices to reflect all the different ways tornadoes can form and the different type (ex cold core versus classic warm front/dryline). Same with supercells and supercell type, etc.

Personally I think weather modeling is proceding well, but sounds like we need finer (more) data input and ways need to be developed for computer modeling programs to recognise the same things that human forecasters look for when making a forecast (such as boundary analysis). If the input grid of data is fine enough, boundary analysis is of high enough quality, then all that remains is to learn and apply all the physical process interactions that the atmosphere can perform and have it combine that into a type of forecast or at least model output products. Probably statistics based on atmospheric simulation and observation / rule based would be the best way to model the output. However as the future progresses perhaps quantum physics / benefits of quantum computing, and principles related to uncertainty would help to anticipate Earth's complicated environment.

Hmmm.....ok, sounds like I've been rambling for awhile. Sorry, but this is pretty cool stuff.
 
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