2024-05-06 EVENT: TX/OK/KS/NE

[Brian McKibben]

This is the old High Risk probability and intensity requirements. Per old standards, yesterday definitely didn't live up to the standard.


A HIGH risk area suggests a major severe weather outbreak is expected, with a high concentration of severe weather reports and an enhanced likelihood of extreme severe (i.e., violent tornadoes or very damaging convective wind events occurring across a large area). In a high risk, the potential exists for 20 or more tornadoes, some possibly F2 or stronger, or an extreme derecho potentially causing widespread wind damage and higher end wind gusts (80+ mph) that may result in structural damage.

 

[John Farley]

Regarding high-risk verification of high wind vs tornadoes, a lot of those wind reports in western MO, when surveyed, will likely be found to have occurred from tornadoes. Have no idea whether that would be enough shift from wind to tornadoes to affect the verification, though I would guess probably not. And would also note that the high risk was not in Missouri.

 

[gdlewen]

P

No. A single violent tornado does not verify an SPC high risk forecast. Forecast probabilities are solely based on coverage of reports, not on intensity. According to the source below, the PP obs yesterday have only verified a 5% for tornadoes so far. More LSRs will likely be added, but it seems extremely unlikely that the max probability contour exceeded will come anywhere close to the necessary threshold for "high", which is 30%.

View attachment 25332

And while I'm at it, I'll go ahead and toot my own horn of vindication after these PP wind probs suggest a high risk would have verified for wind, just as I suspected in my post early yesterday:
View attachment 25333

although a fine point: the Barnsdall tornado was associated with a discrete cell out in front of the line. If I correctly recall the LSR the first reported tornado was in Hominy.


It is ironic that I was in Wellington, KS earlier hoping for discrete supercells ahead of a line and one formed practically in my back yard

 

[Jason N]

Moist Absolutely Unstable Layer -

haha I stopped short of the full description!

 

[Warren Faidley]

For those of you on X, Cameron Nixon wrote a fantastic analysis regarding yesterday's performance.

https://twitter.com/x/status/1787909257549201879

 

[Jeff Duda]

Color me a little surprised that only 8 tornado reports (at least 3 of which were from the same tornado) flanked by 2 others a few hundred km away was enough to satisfy a PP max of over 25%, but there you go. Technically a high would not have verified for tornadoes based on this PP methodology either, although a moderate certainly did.

 

[Jesse Risley]

It's interesting to see some of the SPC employees chiming in with their theories as well, particularly that the ejection of the trough and upper level jet core were such that storms didn't really move off the dry line perpendicular to the shear but rather sort of trained and interfered with each other. Sometimes I don't think to look at cloud features on chase days as closely as I should, but Cameron made a good point about the mammatus present in the downstream environment and how storms were moving into areas where stratus clouds existed from earlier. I wonder if that could have been another fly in the ointment with convective temperatures previously being shown in the upper -80s, something like maybe around 87°, whereas some of those shallow clouds may have held temperatures back in Oklahoma and contributed towards maintaining some of the CINH too.

 

[JamesCaruso]

Question on the Barnsdall / Bartlesville storm - what is the mechanical lifting mechanism for an open warm sector storm like that? Was it outflow from the line to its west? Or general large scale forcing from the upper trough? Some other source?

And is there ever any real basis for targeting a particular spot for an open warm sector storm (other than a boundary of some sort, in which case it’s no longer really an “open warm sector storm”) or is it pretty much a random / chaos theory thing?

 

[Mike Smith]

Question on the Barnsdall / Bartlesville storm - what is the mechanical lifting mechanism for an open warm sector storm like that? Was it outflow from the line to its west? Or general large scale forcing from the upper trough? Some other source?

And is there ever any real basis for targeting a particular spot for an open warm sector storm (other than a boundary of some sort, in which case it’s no longer really an “open warm sector storm”) or is it pretty much a random / chaos theory thing?

In the mid-70's, Steve Tegtmeier, a classmate of mine at OU, did a masters thesis of synoptical climatology patterns that lead to tornadoes. To my knowledge, he was the first to document the "dry line bulge" and "isolated cell ahead of a line." In addition, he told us that solid (as opposed to broken or scattered) lines were less likely to produce major tornadoes. All of this information was new.

Since, I've found his findings to be invaluable when warning of tornadoes. I can't state the physical mechanism for the "supercell ahead of a line" but it -- tragically -- works like a charm.

 

[Jason N]

It's interesting to see some of the SPC employees chiming in with their theories as well, particularly that the ejection of the trough and upper level jet core were such that storms didn't really move off the dry line perpendicular to the shear but rather sort of trained and interfered with each other. Sometimes I don't think to look at cloud features on chase days as closely as I should, but Cameron made a good point about the mammatus present in the downstream environment and how storms were moving into areas where stratus clouds existed from earlier. I wonder if that could have been another fly in the ointment with convective temperatures previously being shown in the upper -80s, something like maybe around 87°, whereas some of those shallow clouds may have held temperatures back in Oklahoma and contributed towards maintaining some of the CINH too.

That was one of the topics discussed prior to the evolution of the High-risk day was the crossover wind orientation from 850 to 500. I noticed and mentioned here about the clouds and ConvT as the day was unfolding as well. I think as you said above, the Anvil overspreading over a more SCT/BKN low level that didn't clear out enough in advance to spike temps may have limited some of the dynamics below the LFC maybe since I think everything above that was certainly more than favorable in terms of large scale lift and shear, and as mentioned by several here now, the timing/location of the initiation, and perhaps sub 1km wind vorticity generation issues IVO the CI location, but that's just a guess there.

 

[Jason N]

Question on the Barnsdall / Bartlesville storm - what is the mechanical lifting mechanism for an open warm sector storm like that? Was it outflow from the line to its west? Or general large scale forcing from the upper trough? Some other source?

And is there ever any real basis for targeting a particular spot for an open warm sector storm (other than a boundary of some sort, in which case it’s no longer really an “open warm sector storm”) or is it pretty much a random / chaos theory thing?

I was watching the observations and radar, and I am not 100% sure, but it appeared as though there may have been a confluence line that initiated the cells, and at the time when they first started to loft, the LLJ was peaking out in a clear zone undisturbed by the line to the west. I didn't see any outflow influence at the time they fired off

 

[Patrick K]

I’ll offer my late thoughts while I wait on a delayed flight. Most of this has already been said in some capacity but here are things I noticed in the OK target area while virtual chasing this event;

1. Storms appeared outflow dominant on radar. I’m curious if this relates to some of the other observations/thoughts.

2. Timing was slightly misaligned with TEC-like storms forming more westward/later than ideal to take advantage of peak heating (which didn’t really materialize as expected anyway)

3. Related to #2, storm orientation was skewed more parallel to the dry line rather than orthogonal as expected. It also seemed like storm motion was slower at times and the combined effect was interference between supercells before they could fully mature and/or become surface based.

4. Once we got an isolated supercell in NE OK, it did go nuts before being absorbed, even despite IIRC appearing to be a bit of a left mover (correct me if I’m wrong, but I thought SRH would be maximized for right movers)

All in all, another tough situation for SPC, getting people to take high risk days seriously.