GRlevel3 Acronyms and Abbreviations

[David Williams]

So I just downloaded the trial version of GRlevel3 (Yes, I am loving it so far). I am really enjoying the program, but since I am somewhat new to meteorology and the technical aspects deciphering weather information. I am totally lost when it comes to those acronyms and abbreviations that show up in the little white boxes next to the overlays on the radar displays and how it has an impact on the storm. Basically, what do I want to see in that little white box so I would be like, "Sweet, it's doing that thing. This should be awesome!"

 

[Ben Holcomb]

What is it you're not sure of? I'm sure there would be a lot of folks here happy to explain to you what each feature is that you're unsure of.

 

[Walt VanRheen]

Like David, I am also a newb to GRlevel3 as well as Meteorology. Has someone created a manual, book or HOW To for this product?

 

[David Williams]

So in the link below for instance (I hope the link worked. If it didn't, I just used the sample image of GRlevel3 that you see when you click on the Help button in the program itself), the mouse is hovering over a purple triangle I assume is a vortex signature. A white box appears next to the signature with acronyms and abbreviations in this order:

Type: TVS
Cell: H8
AVGDV: 26 kts.
LLDV: 58 Kts
MAXDV: 58 kts
hgt: 4800 ft.
Depth: 15600 ft.
Base: 4800 ft.
Top: 20400 ft.
MXSHR: 18 /ks
hgt: 4800 ft.

So, I can take a guess at a few of these... like Type : TVS = Tornado Vortex Signature? But what does Cell: H8 mean? Also, I can guess that Top: 20400 ft. means that the echo tops of precipitation are at 20400 ft.; however, this is the base reflectivity 1 and I don't know how far away the radar is from the storm, but I'm pretty sure that BR 1 can't see much higher that about 10,000 feet into the atmosphere even when the storm is about 120 nm from the radar site. So, how does it know that the heights are at 20400 ft? Well, that's not really an important question here; I'm sure I will figure out the answer to that sooner or later. But, what I am really interested in is figuring out what all those letters and numbers mean, AND what letters and numbers tell me that it is a good set up.

I sincerely appreciate anyone's willingness to explain this to me.

Thanks in advance!!

 

[Greg Blumberg]

Yes, the TVS is the Tornado Vortex Signature, however take it with a grain of salt. Any identifier being shown by radar algorithms exist primarily to jump out at the user to say "Hello, there's something here." It's you yourself who has to look at the base data and interpret it. Humans judgement greatly overrides any radar algorithm.

MXSHR is the Maximum Shear indicated by the TVS velocity couplet. Also remember that TVSs can be triggered by mid level rotation too.

Cell: H8 is the cell identifier. Each individual cell has an identifier so the algorithms can keep track of it. It's similar to naming a hurricane Emily, Andrew, or Ike.

I would not worry about the base and tops information. Those are not really essential to chasing.

I think AVGDV is the average divergence, the LLDV is the low level divergence, and the MAXDV is the max divergence. Not sure though. I don't really use those numbers that much.

The green triangles are hail markers. Those too you ought to take with a grain of salt. The estimated hail size is exactly what it is: estimated. Same thing with the POSH: Probability of Severe Hail.

The other thing is VIL. Vertically Integrated Liquid. I believe this is used sometimes to detect hail. I forget entirely what it is because I don't use it a whole lot. A tip though this tool needs the background knowledge that storms are not always vertically oriented. Supercells have a tilted updraft as do other storms, thus offsetting the algorithm.

A tip: when chasing or using radar at all, start comparing what you see visually to the radar. The best instrument you have is your eyes.

Also, get rid of the smoothing. Look at all of the data. The smoothing is an algorithm as well and thus has downsides.

-----------------------------------------------------------------------------------
Edit: Correction, the LLDV, MAXDV, and AVGDV mean the following:

LLDV = Low-Level Delta-Velocity. This is the gate-to-gate velocity difference (GTG) at the base of the TVS detection (usually 0.5 degree tilt, but not necessarily).

MAXDV = Maximum Delta-Velocity. This is the max GTG for all elevation scans in the TVS.

AVGDV = this is new to me - was not in the NSSL version of the TVS Algorithm (where the WSR-88D version originated). I'm guessing that this is the average GTG across all elevation scans.

I credit Greg Stumpf for answering this question on the past thread: http://www.stormtrack.org/forum/archive/index.php/t-3252.html

Something else: It's not the numbers and letters that make it a good storm to chase. You can't think like that when it comes to radar. You have to take into consideration more than that. Several things I look for are: distance from radar (this will also tell you the height at which you are scanning), any typical radar patterns (i.e. hook echo, hail spike, v-notch, etc..), what each scan at each tilt looks like, what is the velocity data telling you, and the type of air it's in.

 

[Jeff Snyder]

Greg summed things up pretty well. Overall, I use these (Level 3 / NIDS) products with considerable caution. The calculated/derived products that GR2AE perform tend to be more accurate and useful than the Level 3 products. As Greg noted, just use the TVS/meso markers as a quick "hey, you might want to look into this area a bit more"-type of attention-grabber. Perhaps the GENERAL magnitude of the various products can be useful, but don't get caught up on specific numbers.

Honestly, though, I don't pay too much attention to any of those numbers. If you use these products while you chase, or if you follow verification / storm reports much, you'll soon realize to take all of these parameters with a big grain of salt.

 

[Jason Harris]

How do these definitions of the acronyms measure up?
I'd especially like to know if those parameters for judging strength are reasonable like SR 1-25 and MSI greater than 3600 being "very strong"?
It would be great to know for example what the ratings actually were for
tornado-producing storms from EF-0 to EF/F5. (Did the Moore tornadic-supercell have a 3600+ rating?} And, if there are any correlations with likelihood of seeing a wall cloud of notable distinction or rotation based on people's experience of radar vs. visible reality.

I found this a couple weeks ago during a search:
http://tennesseewx.com/index.php?topic=1211.msg22202;topicseen

Due to popular demand, here's the article on MESO icons in GR.

There are two types of mesocyclone icons in GRLevel3:

1) NMD icons - these are the icons you'll see in GR3 1.40 and above when viewing live L3 data and recent archived L3 data. They come from the New Mesocyclone Detection algorithm in the nexrad computer. A solid arrow-ring indicates the meso extended down to the lowest tilt. A broken ring means the meso was not found on the lowest tilt. The color "heat" of the icon represents the strength (very weak is light green, weak is green, moderate is yellow, strong is red, extreme is purple). When you hover your mouse cursor over an NMD icon, you'll see the following information:

Cell: the storm cell ID associated with the NMD
CircId: id for the NMD
SR: 3d strength rank from 1 (very weak) to 25 (end of th e world!)
LLRV: low-level rotational velocity, (Vmax-Vmin)/2
LLDV: low-level delta velocity (gate-to-gate)
Base: lowest altitude of detection ('<' means lowest tilt)
Depth: total height of the rotation ('>' when base has '<')
STMREL: depth of rotation compared to cell heights
MaxRV: maximum rotational velocity in the stack of tilts
hgt: height of MaxRV
MSI: Mesocyclone Strength Index (>3600 is strong)

MSI is the vertical integration of the 2d SRs for the mesocyclone, weighted by the height of each SR so that lower rotations are considered more important. Here are some online papers describing the NMD algorithm and its performance:
http://ams.allenpress.com/perlserv/....1175/1520-0434(1998)013<0304:TNSSLM>2.0.CO;2
http://www.srh.noaa.gov/jan/research/WDSS_MDA/WDSS_MDA.htm
http://nsstc.uah.edu/~tjones/Papers/Jones04_Meso.pdf
http://www.caps.ou.edu/reu/reu03/papers/Christy.pdf

Inside grlevel3.exe are the default nmd icons. If you want to customize them, create a file named nmdicons.png containing two rows of five icons and place it in your GRLevel3 install directory. The top row is shown when the base of a rotation is aloft (ie. not on the lowest tilt) .. The bottom row is shown when the rotation base is on the lowest tilt. On each row there should be five icons representing increasing intensity (very weak, weak, moderate, strong, extreme). GRLevel3 uses the "strength rank", SR, to choose an icon. The first icon is shown for SR values of 1-2, second for SR values 3-4, third for 5-6, fourth for 7-8, and fifth icon for 9 and above. Here is the image used for the default nmd icons:



The aloft icons are dashed rings while the low-based icons are arrow-rings. You can make the icons any size you'd like. GRLevel3 divides the supplied image height by two to get the icon height and image width by five to get the icon width.


2) MESO icons - these are the older Mesocyclone Detection Algorithm icons you'll see on archived data and sites that don't output the NMD product. When you hover your mouse cursor over the icon, you'll see:

Type: the type of rotation detected ("Meso" or "3DC Shr")
Cell: the storm ID of the cell closest to the rotation
Base: altitude of lowest tilt containing rotation (ARL)
Top: altitude of highest tilt containing rotation (ARL)
RAD: radial diameter of rotation (nautical miles)
AZD: azimuthal diameter of rotation (nautical miles)
Shear: strength of rotation in the mesocyclone (1/1000 seconds)

"Meso" is shown for rotations that are seen on 3 or more tilts and "3DC Shr" for those that are seen on only 2 tilts.
---
BTW the cell neear Eastland TX currently only has the "yellow" (moderate) marker for the Meso as of 16:22:48Z
MSI: 2805
SR:5

and the Clarke county MS tor-warned storm has no meso markers at all, nor does it look like much on SRV1. Maybe I didn't see it when it was better. It's puzzling to see what determined that warning. Should one think then that if there is a tornado actually associated with Clarke county that given the storm's embedded nature in a mass of precip and no detected meso that there might have been a landspout--no wall cloud since probably no powerful updraft that is rotating? [as I write this now it has a yellow meso marker and a SR of 5L--what is the "L" for? Now's it's a green (weak) meso with 4 L. Tor warning gone too, so that's one nice resonance between what's on GR3 radar and coming out of NWS.

 

[Greg Stumpf]

It would be great to know for example what the ratings actually were for tornado-producing storms from EF-0 to EF/F5. (Did the Moore tornadic-supercell have a 3600+ rating?)

That would be great, if the EF scale were actually measuring the tornado wind speeds. In other words, the results of such statistics would be mostly useless and this is why we didn't conduct the study.

And, if there are any correlations with likelihood of seeing a wall cloud of notable distinction or rotation based on people's experience of radar vs. visible reality.

"People's experience" is not a direct measurement - wholly subjective. What is one person's "strong rotation" might be another person's "moderate rotation". Also, you can have strong low-level mesocyclones and tornado without a wall cloud. A wall cloud is not a necessary condition.

 

[Jason Harris]

Ok, so there really isn't any empirical data comparing observed conditions with
the radar data? Yes, I know the EF/F are/were damage scales, but it still would be interesting to get a sense of what the readings were for particular storms at the point someone observed a tornado. Also, I brought up the Moore storm in particular because there was the wind-reading with that storm estimated/measured by the DOW of 318 right? And in the absence of that data, I'd still be interested in hearing about people's particular experience, and regarding wall cloud vs. meso--wouldn't the lack of a wall cloud be atypical?
Just knowing the general tendencies would still be practical if not scientifically exact.

 

[Greg Higgins]

"I know the EF/F ARE/were damage scales, but it still would be interesting to get a sense of what the readings were for particular storms at the point someone observed a tornado."

Simple, its impossible. How winds interact with one type of structure is often vastly different compared to another structure based on the way it was constructed. Some builders follow codes and best guidelines and others just throw something together. Therefore, you CAN NOT correlate wind speed and damage until AFTER assessing the construction of the building.

Greg Higgins

 

[Jason Harris]

Basically all I'm asking is just to know what some SR and MSI readings were with some storms of the past that were significant: particulary the Moore storm since we have a wind reading. It would just be great to have some sense of the continuum with chase experiences in term of what the radar readings were vs. observations. Somebody must have that data somewhere.
Even just knowing what SR/MSI/etc. readings are correlated with any storm that produced any tornado.

 

[Todd Brown]

I never get the meso markers on GRL3. The TVS triangle shows up all the time, but I have yet to see the meso rings. I have mesocyclones checked in the storm attribute window. Am I missing something??

 

[Jason Harris]

Hi Todd, Here's a recent image from the storm we were discussing in Texas north of ST. Augustine (before the posts got deleted). See attachment. It would be great to hear some expert analysis of this image--on SRV 1 right near the end of the tornado-warning (and no one claimed anything actually was produced--tornado warned again BTW).

You have all the same things checked? I guess the best bet is to inquire at the message board for GR3?
http://www.grlevelx.com/owners/viewforum.php?f=5

could be specific NMD settings? thread on that:
http://www.grlevelx.com/owners/viewtopic.php?f=5&t=5108

 

[Todd Brown]

Hi Todd, Here's a recent image from the storm we were discussing in Texas north of ST. Augustine (before the posts got deleted). See attachment. It would be great to hear some expert analysis of this image--on SRV 1 right near the end of the tornado-warning (and no one claimed anything actually was produced--tornado warned again BTW).

You have all the same things checked? I guess the best bet is to inquire at the message board for GR3?
http://www.grlevelx.com/owners/viewforum.php?f=5

could be specific NMD settings? thread on that:
http://www.grlevelx.com/owners/viewtopic.php?f=5&t=5108

What version of GRL3 are you currently using? Yeah I have everything checked, but it is just blank next to mesocyclones. TVS/ETVS says 0/0 or whatever there is if there is a TVS symbol. I am in trial mode on GRL3 right now so I can't access the owners forum until I purchase the program? Does the trial version not allow me to view mesos???

 

[Todd Brown]

Here is a screen cap of the Lake Charles, LA radar. There are 4 TVS symbols, but no mesos. Doesn't make sense.