GRLevel3 question

  • Thread starter Thread starter MatthewCarman
  • Start date Start date

MatthewCarman

If this is the wrong thread I apologize.

I have seen on GRLevel3 radar (I am currently using the trail version) icons like 3dcshr and TVS and Meso etc.

I have a understanding of what a TVS and Meso is but what is a 3dcshr (Spelled right?) and how do I use these to determine when a ornado is on the ground?

Also what is POSH on a hail signature? (Green triangle right?) Why are some green triangles filled in or smaller while others are not filled in or bigger?

I just want to understand how to properly read what all I am seeing on the radar. Any help would be apreciated thankyou.
 
Matt,

I believe the POSH = possibility of severe hail. As far as the MDA and Hail icons, the larger the hail, the color changes. If you hover over it with your mouse, it will show estimated hail size. I'm certainly no pro at the GR software, but this might help get you started.

One final note... even with a TVS and the perfect couplet, it still cannot, for certain, tell you that a tornado has formed. That's the whole reasoning for spotters/chasers and what is referred to as "ground truth."

Hope this helps get ya' started. Others please chime in?
 
MatthewCarman said:
If this is the wrong thread I apologize.

I have seen on GRLevel3 radar (I am currently using the trail version) icons like 3dcshr and TVS and Meso etc.

I have a understanding of what a TVS and Meso is but what is a 3dcshr (Spelled right?) and how do I use these to determine when a ornado is on the ground?

Also what is POSH on a hail signature? (Green triangle right?) Why are some green triangles filled in or smaller while others are not filled in or bigger?

I just want to understand how to properly read what all I am seeing on the radar. Any help would be apreciated thankyou.
Click to expand...

3DC is 3-directional correlated shear...3D-UNC is 3-directional un-correlated shear...

TVS- tornado vortex signature and EVTS- enhanced...

POH- possibility of hail and POSH- possibility of severe hail...

i dont really pay too much attention to TVS ETVS 3DC, etc to assess storm rotation...i look at storm relative velocity images for couplets and reflectivity images for hooks and what not...

as far as the hail goes...i dont know what the difference is between the unshaded and shaded images is...i dont really think it matters in my experience with the program...

i like the hail indicators, but like i said...i would rather look at the products then look at the indicators...i dont completely understand everything...just what the acronyms mean...

like the MESO base for example...it doesnt mean anything to me when im looking at the radar...its something that the radar algorithms esitmate and i dont trust completely...and operationally...i dont look at it...

im sure some of the other chasers can break it down better...
 
ETVS and TVS I really don't use. I watch for the Meso and 3d shr markers and then view them in Base Velocity (BV) and Storm Relative Velocity (SRV). For my purposes the ETVS and TVS markers have not been relaiable enough for me to use them. Maybe Greg Stumpf will see this and pipe in as I believe he's had a hand in writing the algorythms that produce these products. He's certainly way more knowledgable than I am on this.

POH = Possibility of Hail
POSH = Possibility of Severe Hail
Both are in percentages and do not represent what's actually happening on the ground.

VIL (Vertical Integrated Liquid) may be a better estimation of hail in a thunderstorm core.

Storm Track markers are helpful in gaging storm motion and speed but can be misleading as they are generally based on the most reflective part of the storm. In the case of a rotating Supercell, it may produce a false direction and speed relative to the actual storm motion as the heavy reflection may actually be moving differently than the entire storm.

Best bet is to view a short loop and gauge the entire picture for motion.

That's my view on it, though I may be technically incorrect on some of the things, it works out for me.

There are others on the board that are much more knowledgable and work with this every day (Greg, Mike U., Rdale, etc.) and give give more technically correct answers.
 
The Level III VIL product is not a good hail indicator - it was specifically developed to FILTER OUT any hail in the processing. GR2AE does not cap VIL and that helps out a bit.
 
really? this is new news to my ears rdale...

what is it for though?

dont values of 50+ mean there is hail going on?

makes alot of since because i just chased a storm with 60+ and it didnt have any hail exept for a few small half inch stones...and some were barely half inch...

i appreciate it man...
 
Last edited by a moderator:
The "L" in VIL explains what it is - vertically integrated LIQUID. The goal of the product is to tell you how much WATER is in the storm, so they cut off high dbZ values as a proxy for not including hail info.
 
Mesocyclone algorithm icons:
"3DC Shear" indicates that there was rotation on two or more tilts.
"MESO" indicates that there was significant rotation on two or more tilts

Hail icons:
Large+filled triangle means POSH >= 50%
Large+unfilled triangle means POSH >= 30%
Small+filled triangle means POH >= 50%
Small+unfilled triangle means POH >= 30%

where POSH = probability of severe hail and POH = probability of hail.

Hail and VIL:
I'm not a meteorologist so there are just my impressions having written code to implement both the VIL and MEHS algorithms. I think VIL is a poor way to look for hail in a cell because it doesn't take into account the temperature aloft during integration. In addition, the default nexrad algorithm intentionally tries to limit the contribution of ice in the integration by capping the dbz at 56. VIL Density suffers from the same defects as plain VIL.

MEHS seems far better to me because it includes the temperatures aloft during integration and gives more weight to the higher reflectivities.

Mike
 
Mike, what is MEHS? I haven't seen that in my GR3.

Matthew, have you registered with the support forums for Gibson Ridge? There are two of them that I'm aware of. One of them is provided by Gibson Ridge, as you would expect. The other is www.grlevelxstuff.com, and it's excellent. If you haven't done so, I encourage you to check them both out. You'll find a lot of helpful information.

Re TVSs, I'm by no means an expert, but for my own two cents' worth, I think they're valuable. As I understand it, they're derived in a different way than shear markers are, and they represent deep and persistent rotation. I rely primarily on SRV, but the more corroboration there is, the better. Pronounced velocity couplets always grab my attention, but add in a TVS and meso markers and to me that says triple-threat.

I might add that in my limited experience with cold-core storms, I can think of at least one instance this year where the GR3 SRV gave no indication of rotation. The only indicators were meso markers and a TVS, and the storm did in fact put down a significant tornado in Indiana.
 
Maximum Estimated Hail Size. I.E. the biggest hailstone expected within the storm. If using the Level III (NIDS) output usually chop about 30% off that value, the GR2AE algorithm is much more accurate.

"I can think of at least one instance this year where the GR3 SRV gave no indication of rotation. The only indicators were meso markers and a TVS"

If it had a meso marker and TVS, the SRV would have shown rotation. It's possible that the storm motion may have confused the display a bit, but those two markers rely heavily on something spinning on the velocity map.
 
Last edited:
ETVS was originally hoped to have some value, but after it was put into operation found to be completely useless so most offices turned it off.
 
You must log in or register to reply here.

Similar threads

Nathan Parker
Notebook Recommendation for Storm Shelter Area
Replies
5
Views
852
Nathan Parker
Nathan Parker
Nathan Parker
Looking for GR Customizations
Replies
3
Views
2K
Nathan Parker
Nathan Parker
JamesCaruso
Minimalist Chase Forecasting: Avoiding Analysis Paralysis and Separating the Signal from the Noise
2
Replies
28
Views
2K
RRogers
RRogers
Nathan Parker
Training for Radar and Forecasting Question
Replies
7
Views
2K
Nathan Parker
Nathan Parker
Dan Robinson
2024-07-29 REPORTS: IL/IN
Replies
0
Views
394
Dan Robinson
Dan Robinson
Back
Top