Possible SVR Today 1/17/2012

[Dave R]

Glad noone was hurt.  Small tornado but folks are even less on guard than usual this time of year.

pic via ohx:

[Thundersnow]

(originally had a reply to this but deleted because it wasn't as clear as it should be. Apologies).

What you saw on CC (with lowering values) from the Hytop radar was not anything tornadic...but rather was the melting layer since at that range (Hytop to Nashville)...the radar is looking up about 7-8kft. You would NOT be able to pick up tornado debris at that range unless it were a very intense tornado...which fortunately is not the case today.

Hytop did sample the very top of a weak meso on velocity, but other than that, nothing of a tornadic nature could be noted. If OHX was online...lower-level data could probably have ruled out something tornadic with that cell anyway...but didn't have the advantage of that Today of course.

I was skeptical of the possible tornado yesterday as well.  However, hindsight makes it hard to fault OHX for issuing that TOR, since we now have ground verification of an EF0 tornado in the path of that cell.

Regardless of any past "over ambition" of issuing TORs, I can understand a cautious/just in case approach yesterday since we were without a local radar and only had distant radar sites to rely on, which didn't give us the best surface reflection.

[ChrisPC]

I thought I saw it on radar. Percy Priest Lake has surely had its share of tornadoes these past few years...

[@NashSevereWx]

KHPX showed decent evidence of rotation at SRV1. Warning was 100% justified. OHX also had TBNA.

On the Centerville storm, OHX did a terrific job canceling it quickly, before the "warned" part of the cell punctured SW Williamson Co and caused huge panic.

I agree with the point made upthread. Functioning dual-pol at OHX would have been fantastic for CC data to confirm the EF-0  tornado may have happened. Yet, CC is only a warning tool to the extent it can "confirm" a tornado continues to churn.  CC is certainly of value, but practically is of little use as a warning tool for short lived EF-0 EF-1s. It will be invaluable data in the event we get a long track tornado.

[Kevin]

KHPX showed decent evidence of rotation at SRV1. Warning was 100% justified. OHX also had TBNA.

On the Centerville storm, OHX did a terrific job canceling it quickly, before the "warned" part of the cell punctured SW Williamson Co and caused huge panic.

I agree with the point made upthread. Functioning dual-pol at OHX would have been fantastic for CC data to confirm the EF-0  tornado may have happened. Yet, CC is only a warning tool to the extent it can "confirm" a tornado continues to churn.  CC is certainly of value, but practically is of little use as a warning tool for short lived EF-0 EF-1s. It will be invaluable data in the event we get a long track tornado.

Wasn't monitoring KHPX at that time...good to know...and obviously with the confirmation it was a good warning.

As you say...and I've emphasized this too (though not in this thread)...the TDS is a debris signatures...which means debris has to be present...which means the tornado is already on the ground. They do not help lead time...but the confirmations that can be added into the warning products and hopefully passed on by the media can be a difference maker in some events. I hope it works that smoothly as I think it can.

Even in spin-ups...while the signatures may be brief and may not mean much for folks downstream if it just lifts right back up...it does aid in the verification process...which is something the NWS needs to improve on especially for those events.

[@NashSevereWx]

Thirsty-for-innovation weather nerds are wise to temper excitement about dual-pol, and save the ticker-tape parades for phased array (ETA: when I jet-pack to work). Dual-pol is untested technology still without fancy third party algorithms.  Even the value parameters are iffy; default “settings” consider life in the plains, rather than TN topography. Everything is still being tested, so to draw any real conclusions now is unwise. 

Still, preliminary data from Atlanta tornadoes shows impressive performance of CC for TDS no more than 60 nm from the radar. As for using CC for TDS, the challenge won’t be as steep for local WFOs as it’ll be for TV/mets in operational settings, who now have yet another thing to look at during a time when their attention is already massively divided during severe events. Trying to explain gate-to-gate sheer – quickly – to a mass audience is already the equivalent of explaining quadratic equations to HS sophomores (most can “get there”, time needed). I don’t really know how you quickly, effectively and accurately describe the meaning of a TDS to a mass audience. Most probably shouldn’t try, but when you have a clear TDS, the temptation will be immense, as will the sense of responsibility to say something about it.

The winter product needs  a lot of work.  I’m hopeful that the true measure of dual pol won’t truly be seen until we figure out what it can and cannot do, and get some good algorithms fired up so that the software reliably interprets the radar for you.

[Charles L.]

The tornado that destroyed one home in Simpson County (KY) and moved into Allen County (KY) was rated an EF-2 with winds of 120 mph...for an area that was only in the "See Text" zone and 2% tornado probs., who would of thought a strong tornado would have occurred?

[ChrisPC]

Dual-pol is definitely a chicken-and-egg situation. We don't have good enough algorithms to interpret all the radar data, but we don't have enough radar data yet to perfect the algorithms. Hopefully, with all the new sites online, we can start learning a lot more.

[Kevin]

Thirsty-for-innovation weather nerds are wise to temper excitement about dual-pol, and save the ticker-tape parades for phased array (ETA: when I jet-pack to work). Dual-pol is untested technology still without fancy third party algorithms.  Even the value parameters are iffy; default “settings” consider life in the plains, rather than TN topography. Everything is still being tested, so to draw any real conclusions now is unwise. 

Still, preliminary data from Atlanta tornadoes shows impressive performance of CC for TDS no more than 60 nm from the radar. As for using CC for TDS, the challenge won’t be as steep for local WFOs as it’ll be for TV/mets in operational settings, who now have yet another thing to look at during a time when their attention is already massively divided during severe events. Trying to explain gate-to-gate sheer – quickly – to a mass audience is already the equivalent of explaining quadratic equations to HS sophomores (most can “get there”, time needed). I don’t really know how you quickly, effectively and accurately describe the meaning of a TDS to a mass audience. Most probably shouldn’t try, but when you have a clear TDS, the temptation will be immense, as will the sense of responsibility to say something about it.

The winter product needs  a lot of work.  I’m hopeful that the true measure of dual pol won’t truly be seen until we figure out what it can and cannot do, and get some good algorithms fired up so that the software reliably interprets the radar for you.

The media should explain the TDS as what it simply is: debris that is due to a tornado in progress. I surely wouldn't get into the technical details...but hopefully any person can understand that debris detected via radar = confirmed tornado and even higher urgency to take shelter. We've seen success with that with the reflectivity debris balls this past year or two and the TDS can be even more effective IMO. Actually...I think it would be easier for a public audience then trying to show velocity images and all those types of products.

A TV station could easily manipulate a color table for CC that it would only need to be shown w/values visible if it were picking up non-met echoes (below about .85)...which in an ongoing event would be either clutter/insects or debris and if the latter would obviously match up with the classic radar products.

Now...how many will actually do that...I have no clue. I do know the NWS is planning to advise of debris within its products and LSR per recent training and hopefully the media will relay that at the least even if they don't know how or can show the actual dual-pol products on-air...and that may not be a necessity if the NWS office is doing its job.

Actually...the TDS is the ONLY situation I would advise media ever employing dual-pol on air. Everything else is way too complicated and muddy. Some TV stations will be tempted to show off HCA as a "precip type" product and that would be a complete disaster since the HCA does not represent surface conditions and the fact its not a very good algorithm at present anyway.

Even without extensive outside testing yet...in the cases where it has been seen its appeared the same in every case. Algorithms are being developed for it...but honestly you don't need them. Its the one thing that abundantly easy to pick out in the raw data if/when its happening.

[Thundersnow]

Storm survey details on Syrma EF0 on Tuesday, including a loop of the velocity echoes picked up by the TBNA radar in Nolensville:

http://www.srh.noaa.gov/ohx/?n=stormsurvey01172012

[Kevin]

Forgot about TBNA. Obviously that helped OHX in the warning process...radar loop pretty clear there.