Deathmatch: Best STP=5

Which STP=5 makes the best chase?

  • [6520J/kg, 150m2/s2, 20kts, 850m, -25J/kg]

    Votes: 0 0.0%
  • [1810J/kg, 415m2/s2, 50kts, 1000m, -50J/kg]

    Votes: 6 28.6%
  • [2145J/kg, 210m2/s2, 35kts, 750m, 0J/kg]

    Votes: 5 23.8%
  • [3515J/kg, 200m2/s2, 40kts, 1200m, 0J/kg]

    Votes: 5 23.8%
  • [4000J/kg, 375m2/s2, 35kts, 500m, -150J/kg]

    Votes: 5 23.8%

  • Total voters
    21
May 25, 2012
211
191
11
39
Albuquerque, NM
www.wxlog.com
I think composite indices are pretty fun, and Sig Tor is a really neat one. Yes yes, these indices are no magic forecasting bullet, they don't have physically meaningful units, they often assume a storm already exists, etc. etc. Another obvious complication is that many different mixes of the properties can give the same index value.

But that's also the fun part. All of the poll choices give a decent STP of 5. All other things equal, which STP=5 would be your favorite for a chase day? Is there a better STP=5 that I didn't include?

Note: Poll choices are [MLCape (J/kg), ESRH (m2/s2), EBWD (kts), mlLCL (m), mlCINH (J/kg)]
 
Dec 8, 2003
1,395
409
11
Southeast CO
www.youtube.com
I am of the camp that for an epic tornado day it's best to have a nice balance of parameters present, and also that one single parameter too low or too high can ruin everything else. For me that immediately eliminates choices 3, 4 and 5. With no cap in choices 3 and 4 I would expect either a) widespread rain fouling the synaptic environment early on or b) dicrete cells not given time to mature into supercells before the evolution of a crapfest MCS. As for #5 I would expect a cap bust, and even if that can be avoided (orographic lifting, say?) then I would expect the 4000 J/Kg + 500m LCL to completely overwhelm the 35kts of venting to result in some serious HP problems.

Okay so 1 or 2?

#1 is, similarly, a scenario whereby absolutely huge instability and weak helicity coupled with ridiculously weak venting is going to be a mess. I wouldn't drive more than an hour to chase this forecast.

So do I vote for #2? Yep, although I would be pretty concerned that that much helicity and venting would rip apart any aspiring updrafts. The level of helicity and and venting suggest that you have a really dynamic system that will overcome that cap to get initiation, but if I had my druthers I'd wish to tone down the dynamics and pump up the instabilty a couple notches for a better balance.

Great thread idea!
 
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Jan 14, 2011
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St. Louis
stormhighway.com
I chose #5 simply due to it being close to the Bennington setup - big CAPE, slow-moving storm/tornado anchored on a boundary. Some HP issues, but sporadically so. #3 and #4 seem less desireable due to lack of capping - unless that zero cap is very localized. #2 is early season outbreak with fast-moving storms, and #1 is a late-season HP monster.

That said, I'd chase all of them if given the opportunity. They all have drawbacks, but none that would make me stay home if I had the funds and time.
 
Last edited:
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May 25, 2012
211
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39
Albuquerque, NM
www.wxlog.com
Thanks @Bob Schafer and @Dan Robinson! Those were exactly the types of insights I was hoping to get. I thinks it's interesting that neither of you chose #3 or #4 due to zilch capping. Totally makes sense. What would you consider to be the ideal cap? -50 J/kG?

The STP calculation gives the best score to a 0 mlCINH (all other things equal), so it would be neat to study its discriminating ability if that term was modified to penalize STP for either too much or too little cap.
 
Dec 8, 2003
1,395
409
11
Southeast CO
www.youtube.com
What would you consider to be the ideal cap? -50 J/kG?.
My forecasting skills aren't good enough to get that specific. All I know is that when I'm in the process of making a chase/no chase decision before a potential event I don't want to see a total lack of any cap. I won't be too concerned if there's little or no cap at 00Z, but if it's missing early in the afternoon I am really skeptical about the day's potential.
 

Mark Gressman Jr

Enthusiast
May 12, 2022
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4
1
38
South Jersey
Apologies for resurrecting an old thread, but I thought this was an awesome idea! I'm currently working my way through all the posts on this site to glean as much wisdom as possible, and I was surprised to see only a few replies here. I think the logic behind the choices was already expressed well by Dan and Bob, but I figured it would give some of the newer members a chance to chime in too if they haven't seen it.

With my limited knowledge and without knowing the larger picture, I'd personally choose #2, as a moderate cap would hopefully keep things discrete. With such high helicity, I'd think anything that went up would stand a chance at producing, thus spacing out chasers. Having a higher LCL would hopefully give better visibility from a higher base and possibly be more photogenic. And although 50kts might be too fast to have a leisurely chase, with proper position, it might also help keep convergence down as well. Would the lower CAPE have any effect on lowering the chances of severe hail? Really interested to see others opinions on this.