TVS and Tornado Warning

[Travis W Speakman]

Unfortunately, I'm armchair chasing this nice outbreak happening in KS/MO right now. I was watching a cell in a squall that developed some rotation and then was tagged with a TVS for 2 complete scans. Grant it, it wasn't a very strong delta change, around 53kts max with 20kts sheer. But my question is, why wouldn't such signature trigger a tornado warning? Both the SRV1 and 2 scans showed it, and it had a base of 3800ft with a height of 13100ft of a 23500ft cell. Is there a sustained amount of time that needs to be met on a TVS to qualify for a "doppler warned" storm...or am I completely missing the boat?

Thanks!

 

[Travis W Speakman]

Okay...now I'm confused. Just got a tornado warned storm out of this outbreak and I captured an image from GR3 so you all can hopefully help me out. Just like my previous question of how you can have a TVS with close and tight couplets and not have a tornado warning; how can you have a tornado warning without close and tight couplets indicative of a TVS? This image doesn't look near as tight as the TVS, obviously. And I can see the circulation, but again, it looks broad and not as big of a gate to gate change as the TVS was. So how does that get a tornado warning and the TVS didn't???

 

[David Draun]

The warning meteorologist watching the radar is also informed of the characteristics of the environment the storm is in. Sure, a storm can have nasty rotation and trigger a TVS, but if the storm is elevated above a stable layer, then no TOR.

 

[Travis W Speakman]

The next scan makes sense why it was tornado warned! But, my question still stands...shouldn't this one have a TVS on the gate to gate change now seen?

 

[John Wetter]

Tons of TVS's happen with no TOR's. Tons of TOR's happen without TVS's. As mentioned, the warning meteorologist is taking a lot of environmental and radar signatures into consideration. IIRC, that storm had a more divergent signature to it for some time, even at the beginning of the TOR, but it did get it's act together better.

 

[rdale]

The next scan makes sense why it was tornado warned! But, my question still stands...shouldn't this one have a TVS on the gate to gate change now seen?

A TVS is NOT the same as gate-to-gate. GtG is not required for TVS and vice versa.

Remember a TVS is simply radar data that goes through an algorithm and meets the criteria. Its goal is simply to help the meteorologist by grabbing his attention and saying "look at me." It is not a sign of a tornado.

 

[Travis W Speakman]

A TVS is NOT the same as gate-to-gate. GtG is not required for TVS and vice versa.

That confuses me. I guess I really need to dig in depth on how 88D works, or rather on how to interpret it on a level that's above my current one because I just know the basics. I know TVS stands for Tornado Vortex Signature and gets triggered by gtg of at least 45kts inbound next to 45kts outbound. And that doesn't necessarily mean a tornado is on the ground, as the only way that can really be verified is by sight.

I guess I'm kind of answering my own question as I talk, but when the TVS was tripped, it was obviously a tight gtg with a delta change of 53kts. Yes, that doesn't mean a tornado is on the ground, only that strong and tight rotation is present. Shouldn't that have gotten warned as a precaution because of the tight signature?

But on the tornado warned storm, there was rotation I could see, but no tight gtg that triggered a TVS. I guess it's possible to have a brief tornado called in confirmed that would get the warning, but this particular storm warning said "doppler radar indicated a tornado." If that was the case, would it not need a tighter and stronger rotation than what it had?

So I guess in a round about way, I answered my own question but came up with a new one. If the tornado warned storm had a gtg less than TVS requirements, why wasn't it labeled with a meso signature instead and why the warning in the first place? My mind says a tornado warned storm with less than TVS requirements implies a really weak rotation and should get a meso label. Obviously, that's not the case as the meteorologists know what they're talking about! I just don't understand the process behind it and I guess am looking at it for face value.

Thanks for your explanations! I'm still pretty new to radar interpretation!

 

[Jeff Duda]

Travis,

The TVSs that go off are just output from the TDA (Tornado Detection Algorithm). The settings are adjustable according to the environment. You should read the following paper because it fully discusses how the TDA works:

http://ams.allenpress.com/archive/1520-0434/13/2/pdf/i1520-0434-13-2-352.pdf

The TDA's sister, the MDA, does similar things. Here's a link to that paper:

http://ams.allenpress.com/archive/1520-0434/13/2/pdf/i1520-0434-13-2-304.pdf

 

[rdale]

Jeff has it right - the met's don't "label" storms with a TVS or Meso. That's all automated output.

If a meteorologist analyzes radar along with the environment and thinks there could be a tornado, but no spotter has seen one, he issues a "radar indicated" warning. It doesn't meant that there's a TVS, or GtG, or anything like that. Just means he thinks there is a tornado but nobody has actually witnessed it.

 

[Travis W Speakman]

Sweet, thanks for the replies! Those articles helped a lot. I knew that TVS's were computer generated, but I didn't know the parameters in which they operated. Thanks a lot, that makes a lot more sense!