Severe Weather Threat 5/25-5/26, 2024

[jiharris0220]

No, it isn't.

Agreed, nothing about 30-40knots of low level jet winds before 0z is “weak”. That’s more than enough especially with the cape values for strong/violent tornadoes.

 

[slenker]

I slightly disagree here, I don't think 5/3/99 is a good analog as the type of trough is rather different the placement of the surface low is forecasted to be further south than it was that day. Also different than 5/20/19.

I didn’t mean that I believe the analog is similar, I actually agreed with what you were saying here. Sorry if I had confusing wording with my initial claim.

 

[KCweatherboy]

No doubt. My only contention is that I think tomorrow will be similar to 6 May: overall underperformance relative to expectations, but with one lone supercell that produces a potentially violent/devastating tornado (or two). Given the absence of big outbreaks in this region for a long time, along with a number of “busts” along the way, I would need to see overwhelming indication of a major event before agreeing with a HIGH TOR-wise. Only resolution of mesoscale factors on day one can really address the uncertainty. Until then I will be quite skeptical.

Low-level shear looks to be somewhat weak before 00Z, so timing is an issue, along with the cap. However, in this case overall shear vectors relative to the dry-line look much more conducive than on 6 May, and we will be dealing with a robust surface low as well. Overall the setup definitely seems to offer more potential for widespread discrete mode than 6 May. I would like to see some indication of a weaker EML and better-timed forcing, possibly among some other things, to be really confident as to the likelihood of a HIGH verifying.

I wouldn't say it's been a long time. The type of outbreaks you've always talked about only happen once in a blue moon. The last ones being 5/24/11, 5/3/99, and 4/26/91. Before that though, you could argue you have to go back to 1955 to find that level of an outbreak (unless I'm missing one) in Oklahoma. There is going to be a natural variance in the duration between outbreaks simply due to statistics, and it's certainly possible that having 3 events as large as those in the past 30 years is a statistical anomaly.

 

[KCweatherboy]

I didn’t mean that I believe the analog is similar, I actually agreed with what you were saying here. Sorry if I had confusing wording with my initial claim.

Gotcha, I might have misinterpreted what you were saying too. This is certainly a high potential with this event despite the differences!

 

[jiharris0220]

18z nam has a bit more convective coverage from Texas to Oklahoma, definitely not trending the right direction.

 

[MMWX]

It's graduation season too. I hope this underperforms but the fact that the SPC almost issued a D2 high (which I've never seen in my limited time watching the weather) is pretty scary. Very active weekend ahead for both people and the weather.

 

[Kds86z]

It's graduation season too. I hope this underperforms but the fact that the SPC almost issued a D2 high (which I've never seen in my limited time watching the weather) is pretty scary.

I was thinking same. That and holiday weekend

 

[Tempestas Tonitrua]

No doubt. My only contention is that I think tomorrow will be similar to 6 May: overall underperformance relative to expectations, but with one lone supercell that produces a potentially violent/devastating tornado (or two). Given the absence of big outbreaks in this region for a long time, along with a number of “busts” along the way, I would need to see overwhelming indication of a major event before agreeing with a HIGH TOR-wise. Only resolution of mesoscale factors on day one can really address the uncertainty. Until then I will be quite skeptical.

I mean, isn’t this basically the definition of the gambler’s fallacy? One of these WILL verify. It may or may not be tomorrow, but, just because there have been a string of under-performers in your opinion doesn't have an impact on each new setup. Well, unless the logic behind your statement is your “theory” and if that’s the case I’m not even discussing this.

Edit: and you know what, I agree with you on the mesoscale point. On those high end days, a lot of times, it comes down to the mesoscale factors taking advantage of the synoptic background and set up.

 

[NorthGaWeather]

Yeah I don’t think 5/3/99 is a good analogy here. That was a case where things came together the day of to elevate what looked like a run-of-the-mill May severe weather day in Oklahoma up until that morning. This is…not that.

Can’t see much reason not to go high on the first outlook tomorrow unless something majorly changes or they really aren’t sure if the cap will break. Very scary setup, not much else to say at this point.

Exactly. The trough and associated wind fields were significantly under valued for this event. Issues with initiation were present, but were not the main issue. As evidenced by the Vortex 99 status messages supercell initiation was likely, but they didn't expect many, if any, tornadoes with initiating thunderstorms. Once profiler data resolved the shortwave/wind fields, that vaporized and the rest is history.

 

[MMWX]

I mean, isn’t this basically the definition of the gambler’s fallacy? One of these WILL verify. It may or may not be tomorrow, but, just because there have been a string of under-performers in your opinion doesn't have an impact on each new setup. Well, unless the logic behind your statement is your “theory” and if that’s the case I’m not even discussing this.

Downplaying severe weather because "It hasn't happened here in a while" is so stupid. ESPECIALLY in the middle of the classic Tornado Alley during one of the most volatile setups I've ever seen.

 

[NorthGaWeather]

It isn’t bad to have expansive storm coverage, it seems like the truly long track violent tornadoes start by having dominant cells go through either a merger or get nudged by the cell behind it.

April 27, 2011 was a semi discrete mode and didn’t have the issues that May 6 had, and we know how that went.

I’m anxious for the 18z runs to see changes occur if any.

Completely agree. Most significant events in the Southern U.S. are of a semi discrete mode. In fact, if memory isn't failing me, the number of truly discrete events in the South is rare. Much more common in the Central Plains though.

 

[slenker]

I feel like there’s a bit of hostility here. I haven’t heard him “downplaying” it, he just seems skeptical, which isn’t necessarily a bad thing - it’s always important to try to see what could go “wrong” with this setup tornado wise. However, I’m starting to believe that this event is going to be really nasty and I’m switching to a more bullish prediction compared to what I was originally concerned about.

 

[Tempestas Tonitrua]

I feel like there’s a bit of hostility here. I haven’t heard him “downplaying” it, he just seems skeptical, which isn’t necessarily a bad thing - it’s always important to try to see what could go “wrong” with this setup tornado wise. However, I’m starting to believe that this event is going to be really nasty and I’m switching to a more bullish prediction compared to what I was originally concerned about.

I’m not going to elaborate further, but that user has a “history” on this board.

 

[Tempestas Tonitrua]

Completely agree. Most significant events in the Southern U.S. are of a semi discrete mode. In fact, if memory isn't failing me, the number of truly discrete events in the South is rare. Much more common in the Central Plains though.

Yep, a lot of southern events are grungy and messy in some ways. 4/27/11 was anomalous in that regard. Dryline initiation, capping, subtle forcing, and little areas of confluence. Sounds like I’m talking about Oklahoma but these were all present in LA/MS/AL on 4/27/11.

 

[Clancy]

Completely agree. Most significant events in the Southern U.S. are of a semi discrete mode. In fact, if memory isn't failing me, the number of truly discrete events in the South is rare. Much more common in the Central Plains though.

I actually just saw a post by Cameron Nixon earlier where he was discussing how it seems like the vast majority of significant tornadoes come from interactions where an initially crowded space consolidates into a single, dominant cell, a phenomenon we often see in some (though certainly not all) setups with high convective coverage.

 

[wx_guy]

Thought I'd point out the 12z HREF --> Very high potential (CAPE 5k+ in much of the area) but may have limited storm activity. I suspect we'll have a handful or less of really, truly horrifyingly potent storms but not much else. Just a prediction.

 

[Clancy]

Thought I'd point out the 12z HREF --> Very high potential (CAPE 5k+ in much of the area) but may have limited storm activity. I suspect we'll have a handful or less of really, truly horrifyingly potent storms but not much else. Just a prediction.

I reckon that's among the more probable outcomes and, again, one of those situations where the few places unlucky enough to be in the path of one of these things will have a bad time.

 

[Fred Gossage]

Tomorrow is one of the events that argues that, as long as we're confident that the low number of storms won't end up being only one singular storm, there doesn't need to be so much focus on having a swarm of violent EF4+ tornadoes in order to trigger a High Risk. If that's the way things are going to be handled from here on out (needing a swarm of violent tornadoes for a High Risk, that is), it's an intentional breaking of the climatology of the convective outlook system that's been in place since before I was born. Going all the way back to the initial inception of those categories in 1982, it was never intended to be that way. Days where there ends up being a handful of smaller tornadoes alongside one or two that are full-blown violent EF4-EF5 should constitute a "lower-end" High Risk (it always did from 1982-2014 at least), and I have a feeling tomorrow in Oklahoma may show you why that's the case.

 

[CheeselandSkies]

Tomorrow is one of the events that argues that, as long as we're confident that the low number of storms won't end up being only one singular storm, there doesn't need to be so much focus on having a swarm of violent EF4+ tornadoes in order to trigger a High Risk. If that's the way things are going to be handled from here on out (needing a swarm of violent tornadoes for a High Risk, that is), it's an intentional breaking of the climatology of the convective outlook system that's been in place since before I was born. Going all the way back to the initial inception of those categories in 1982, it was never intended to be that way. Days where there ends up being a handful of smaller tornadoes alongside one or two that are full-blown violent EF4-EF5 should constitute a "lower-end" High Risk (it always did from 1982-2014 at least), and I have a feeling tomorrow in Oklahoma may show you why that's the case.

April 27, 2011 skewed many perceptions of what a high risk day should be, it was extreme even by the standards of that risk category. However, with the increased rarity (assuming a desire for increased confidence and to reduce the likelihood of a perceived "Forecasted Convective Amplification Deficiency") with which SPC has applied the high risk after 2014 it is quite remarkable that all three issued in the classic "Tornado Alley" Plains region (in May 2017, 2019 and now in 2024) actually have underperformed or by some perceptions "Atmospheric Anti-Climax."

My old interpretation of an "ideal" high risk day in terms of forecast verification was something like Veteran's Day 2002, May 4, 8 and 10, 2003, Super Tuesday 2008 (ironically, a high risk was also put out on May 22nd that year, but it was the following day, IIRC a moderate risk, that produced a truly extraordinary tornado wedge swarm in Kansas that somehow avoided much of any impact on population centers) or April 24 and May 10, 2010.

 

[KCweatherboy]

April 27, 2011 skewed many perceptions of what a high risk day should be, it was extreme even by the standards of that risk category. However, with the increased rarity (assuming a desire for increased confidence and to reduce the likelihood of a perceived "Forecasted Convective Amplification Deficiency") with which SPC has applied the high risk after 2014 it is quite remarkable that all three issued in the classic "Tornado Alley" Plains region (in May 2017, 2019 and now in 2024) actually have underperformed or by some perceptions "Atmospheric Anti-Climax."

My old interpretation of an "ideal" high risk day in terms of forecast verification was something like Veteran's Day 2002, May 4, 8 and 10, 2003, Super Tuesday 2008 (ironically, a high risk was also put out on May 22nd that year, but it was the following day, IIRC a moderate risk, that produced a truly extraordinary tornado swarm in Kansas that somehow avoided much of any impact on population centers) or April 24 and May 10, 2010.

If anything, I feel like events like 4/27/11 and 4/3/74 belong in their own separate "extreme" risk category to truly convey the significance of those events. Days where it is well forecasted that it is going to be a very very bad day.

I think your interpretation of a high-risk day is exactly what it should be imo, but it doesn't feel like a high-risk means that anymore to the public, which is unfortunate.