Deathmatch: Best STP=5

[StephenHenry]

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)]

 

[James Hyde]

This is a really interesting way to think about chaser preferences. The results should be interesting.

 

[Bob Schafer]

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!

 

[Dan Robinson]

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.

 

[StephenHenry]

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.

 

[Bob Schafer]

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]

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.

 

[Jeff Wright]

Has a hurricane ever made landfall during a classic outbreak?

 

[Andy Wehrle]

Has a hurricane ever made landfall during a classic outbreak?

Unlikely, since the "classic outbreak" tornado season (April, May, early June, at least in theory) doesn't really overlap with the peak of hurricane season (August, September, October). Land-based storm chasers don't really like the prospect of an early season Gulf tropical cyclone in May or early June, as it can mess up the moisture trajectories.

 

[Sam Soud]

I think the people dissing on 3/4 are missing some points. Even if the cap is zero earlier in the day, you still need forcing. In that case, it comes down to trough timing. 3/4 are great chases if the trough is timed well with peak heating in the afternoon hours, because your forcing will arrive at the right time. That being said, 3 is better than 4 with very good LCLs and what is probably more subtle forcing.

I guess the problem with this whole exercise is that all of these setups can be good and bad based on numerous other factors, and it's impossible to control them all.

 

[Mark Gressman Jr]

@Sam Soud I definitely agree that it's completely subjective depending on how you interpret what constitutes a better chase. I bumped the post because I really liked the idea, and thought it was interesting to see other forum members logic when making a choice. If we assume that forcing was timed perfectly for all the choices, would you still choose either of the 2 with zero cap? To me, it would come down to how large the area encompassed by the STP was, and what the parameters were around said area. If it's super localized with poor surrounding parameters, I'd imagine we'd be in good shape, but then everyone else would join the party and sitting in a chaser conga line isn't my cup of tea. Any larger area would likely have stuff going up everywhere, potentially fouling up inflow. I'd think in that scenario, the best bet would be to get to tail end charlie.... and you'd be where everyone else was again. I think the best case for zero cap would be a lack of forcing, and hoping for a localized area within the STP to reach convective temperature. Not sure how that would work with my fragile grasp of the basics, maybe someone else could chime in. I could also be completely wrong about everything, lol... if so, please feel free to correct me.

 

[Sam Soud]

@Sam Soud I definitely agree that it's completely subjective depending on how you interpret what constitutes a better chase. I bumped the post because I really liked the idea, and thought it was interesting to see other forum members logic when making a choice. If we assume that forcing was timed perfectly for all the choices, would you still choose either of the 2 with zero cap? To me, it would come down to how large the area encompassed by the STP was, and what the parameters were around said area. If it's super localized with poor surrounding parameters, I'd imagine we'd be in good shape, but then everyone else would join the party and sitting in a chaser conga line isn't my cup of tea. Any larger area would likely have stuff going up everywhere, potentially fouling up inflow. I'd think in that scenario, the best bet would be to get to tail end charlie.... and you'd be where everyone else was again. I think the best case for zero cap would be a lack of forcing, and hoping for a localized area within the STP to reach convective temperature. Not sure how that would work with my fragile grasp of the basics, maybe someone else could chime in. I could also be completely wrong about everything, lol... if so, please feel free to correct me.

You'd want it to be subtly forced. That's the thing about this entire exercise, it's all still very dependent on other factors. 3 might be better, but 35kts at 500mb can be very subtly forced or powerfully forced depending on the rest of the windfield and what boundaries are present in the area, synoptic or mesoscale.

 

[Andy Wehrle]

Since there have already been several insightful replies to the original post, I'm curious to know if these scenarios are taken from actual environments and if so, what the outcomes were.

 

[Mark Gressman Jr]

Any scenario I put forth was totally hypothetical based on what I've learned thus far. I was kinda hoping if anyone corrected me, it would be another avenue to understand where I was off base. I've only ever tested my forecasting by setting a target and chasing through the computer... so far. I don't wanna be a part of the crowd who gets ass over head and end up in trouble. I get more than enough gratification from piecing the physics together, and being able to visualize the bigger picture. This forum, and all the members who've taken their time to add meaningful responses has went a long way towards accomplishing that goal!

As far as the poll choices, I have no idea where to find that info.... but it would be interesting though.