Severe Weather Threat - May 6, 2024

[Casuarina Head]

SPC AC 040729

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0229 AM CDT Sat May 04 2024

Valid 061200Z - 071200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN/CENTRAL PLAINS...

...SUMMARY...
Numerous severe thunderstorms will likely develop and move eastward
Monday afternoon and evening across parts of the southern/central
Plains. Strong tornadoes, very large to giant hail, and damaging
winds all appear possible.

...Synopsis...
A negatively tilted upper trough with embedded 50-70 kt mid-level
speed maximum will eject northeastward across the northern/central
Plains on Monday. At the surface, the primary low should consolidate
over the northern High Plains of eastern MT/western ND and vicinity,
with a secondary surface low possibly developing over the central
High Plains by Monday evening. A rather moist low-level airmass,
with surface dewpoints generally in the mid 60s to low 70s, will
spread northward across the southern/central Plains ahead of an
eastward-mixing dryline. A warm front should eventually extend
eastward across parts of NE/IA, and this boundary will probably be
the northern limit of appreciable severe-thunderstorm potential.

...Southern/Central Plains...
A severe-weather outbreak still appears possible across parts of the
southern/central Plains on Monday, focused from south-central/
southeast NE into central/eastern KS and much of OK. Robust diurnal
heating of the moist low-level airmass, coupled with steep mid-level
lapse rates overspreading much of the warm sector, will likely
foster moderate to strong instability (MLCAPE generally ranging from
2000-3500 J/kg) by Monday afternoon. Enhanced mid-level winds and a
favorably veering/strengthening wind profile with height through
mid/upper levels will support around 40-55 kt of effective bulk
shear, stronger with northward extent in KS/NE.

Current expectations are for scattered supercells to erupt along the
length of the dryline in south-central NE and western/central KS by
mid to late Monday afternoon, coincident with stronger large-scale
ascent overspreading this region. Given the rather favorable
thermodynamic and kinematic parameter space, very large to giant
hail (2-4 inch diameter) will likely be a threat with these initial
supercells. The threat for tornadoes should quickly increase through
the late afternoon and early evening in tandem with a strengthening
southerly low-level jet. Ample 0-1 km and effective SRH shown in
various NAM/GFS forecast soundings suggest a threat for strong
tornadoes with any supercell that can remain discrete. With time
Monday evening and into early Tuesday morning, upscale growth into
multiple linear structures is probable, with an increased threat for
severe/damaging winds, along with embedded tornadoes given the
forecast strength of the low-level shear.

The southward extent of the substantial severe risk into OK and
north TX remains somewhat uncertain, as better forcing for ascent
will tend to remain across the central Plains. Still, modest
mid-level height falls should encourage isolated to perhaps widely
scatted supercells developing along the length of the dryline into
the southern Plains. Very large hail and strong tornadoes will be
the main threats with any supercell that can develop and persist
across this region Monday afternoon/evening. Model trends will also
be monitored for a more favorable corridor of strong tornadoes and
giant hail, which may necessitate greater severe probabilities for
Monday in a later outlook.

..Gleason.. 05/04/2024

I am curious: which models are being referred to here? The 00Z EPS continues to strongly favour a more-linear solution due in part to occlusion.

 

[tennessee storm chaser]

Meg already mentions tornadoes their forecast area ….

 

[tennessee storm chaser]

I am curious: which models are being referred to here? The 00Z EPS continues to strongly favour a more-linear solution due in part to occlusion.

The ukie and gfs are showing super cellular activity out ahead dryljne… the euro slowly caved more to that scenario… but plenty time iron things out for sure

 

[Casuarina Head]

The NAM is still a dangerous solution, 84-hour modelled convective mode aside.

The bigger concern I have re: Monday is the degree of occlusion of the main upper low and separation from the jet streak that rounds its base later in the day. The 12z Euro shows this well, with a lack of "focus" to the main belt of mid/upper level flow (helps sharpen the dryline) and relatively meridional mid level flow. This would be less favorable for long lived supercells and encourage upscale growth. IMO, the Euro would not be a top tier event, but would probably still yield some significant severe. To get the high end, the trough needs to be a bit more focused on the southern end and stay more of an open wave as it ejects (something perhaps akin to the 12z UK, GFS, or Euro AIFS solutions).

Re: Monday’s potential, I’m just curious as to when the south-central Plains of TX/OK/KS will finally see a HIGH-Risk EF2+ event again. In this area I can’t think of any event since 2013 or so that really seems to have met all the criteria for a HIGH in terms of EF2+ tornadoes, though I am probably overlooking an event or two, and my interpretation of the criteria may be/is likely wrong. (Obviously probability has nothing to do with the potential for a damaging, destructive event, regardless.) Here is my view of the criteria, based on the wording of official and/or reliable sources:

https://www.spc.noaa.gov/misc/about.html

4-MDT (red): widespread severe weather with several tornadoes and/or numerous severe thunderstorms…some of which should be intense.
5-HIGH (magenta): numerous intense and long-tracked tornadoes…high confidence exists in widespread coverage of severe weather with embedded instances of extreme severe…violent tornadoes

E/F scale: “strong/significant” E/F2+, “intense” E/F3+, “violent” E/F4+
“Several”, “numerous” imply three or more, “some” two/a pair (=few)?

https://www.spc.noaa.gov/publications/broyles/longtrak.pdf

A map of the United States from 1880 to 2003 was constructed showing normalized frequencies of F3 to F5 tornadoes with path lengths of at least 25 miles.

https://www.ustornadoes.com/2014/04/11/long-track-tornadoes-historical-clues-about-intensity-plus-where-and-when-they-occur-most/

use 25 miles as a base

For EF2+ tornadoes*, this is my interpretation of the above information (please feel free to correct me):

MDT Risk: features many tornadoes (incl. several EF2+?), a few “intense” (EF3+), usually numerous supercells
HIGH Risk: features many intense (EF3+), long-lived (PL ≥ 25 mi) tornadoes, including multiple violent (EF4+)

For example, the most recent event in this region...

27 Apr 2024: 7 EF2+ (3 EF3+, 1 EF4+), 2 EF3+ w/ PL ≥ 25 mi

...does not seem to have fulfilled all the criteria?

The ukie and gfs are showing super cellular activity out ahead dryljne… the euro slowly caved more to that scenario… but plenty time iron things out for sure

I am referring to the Euro ensemble mean rather than the operational run. So far the EPS seems to be trending away from an upper-tier TOR event on Monday. The UA pattern on the EPS seemingly supports too much of an occlusion to allow for a HIGH Risk (“upper-tier”) TOR-wise, and if anything, the most recent run seemingly shows the most pronounced occlusion yet.

 

[UK_EF4]

CSU guidance seems very aggressive on a major 3 day severe weather outbreak:





Personally, there do seem to be multiple possible failure modes/limiting factors in terms of tornadoes, and right now I am not anticipating anything huge, although a high ceiling exists on all three days so its important to be very vigilant. However at least in terms of hail and wind, next week looks significant.

 

[tennessee storm chaser]

CSU guidance seems very aggressive on a major 3 day severe weather outbreak:

View attachment 26288
View attachment 26289
View attachment 26290

Personally, there do seem to be multiple possible failure modes/limiting factors in terms of tornadoes, and right now I am not anticipating anything huge, although a high ceiling exists on all three days so its important to be very vigilant. However at least in terms of hail and wind, next week looks significant.

Be honest at this range to early be sure , but a severe weather event of all modes looks very possible for least Monday to Tuesday . Wednesday needs be watched very closely also . Things get clearer as we draw closer next week

 

[UK_EF4]

Be honest at this range to early be sure , but a severe weather event of all modes looks very possible for least Monday to Tuesday . Wednesday needs be watched very closely also . Things get clearer as we draw closer next week

You are definitely right, this period of Day 3-5 can often be quite unclear in terms of what's going to happen with lots of model changing. Probably better for me to adopt more of a wait and see mindset.

 

[Casuarina Head]

CSU guidance seems very aggressive on a major 3 day severe weather outbreak:

Personally, there do seem to be multiple possible failure modes/limiting factors in terms of tornadoes, and right now I am not anticipating anything huge, although a high ceiling exists on all three days so its important to be very vigilant. However at least in terms of hail and wind, next week looks significant.

Undoubtedly Monday and Tuesday both look to be quite significant wind- and hail-wise, thereby meriting attention for these alone. Re: Monday, I was only speaking about the dearth of top-tier tornado outbreaks over the south-central Plains for nearly a decade or so, which has been talked about by others, i.e., professional meteorologists, climatologists (Thomas P. Grazulis), and chasers. Even if truly historic events are infrequent, high-end, HIGH-Risk-worthy tornado outbreaks have historically tended to occur more frequently on a decadal basis regionally than we have seen since 2013 or so. I am just wondering as to when big tornado outbreaks will finally start to return to this part of the Plains. So I am asking: what are the odds that the Euro ensemble mean will swing toward a top-tier tornado scenario for Monday at this range?

 

[Clancy]

D3 areal outlook; large 15% highlights for D4 and D5; mid-range disco.

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Sat May 04 2024

Valid 071200Z - 121200Z

...DISCUSSION...
An active period of organized severe thunderstorms should persist
into at least the middle of next week across parts of the southern
Plains into the mid MS Valley, Mid-South, and Midwest/OH Valley. The
15% severe areas for both Day 4/Tuesday and Day 5/Wednesday have
been expanded based on latest model trends.

...Day 4/Tuesday...
The primary upper low over the northern Plains is forecast to
gradually occlude on Tuesday. But, a strong mid-level jet streak
should overspread parts of the mid MS Valley and Midwest through the
day. A secondary surface low should develop northeastward across
these regions, with a warm front also lifting northward towards
southern WI and southern Lower MI. Thunderstorms related to
low-level warm advection and activity that has spread eastward from
the southern/central Plains may be ongoing Tuesday morning. It
remains unclear if these thunderstorms will strengthen once again as
they develop eastward in tandem with a destabilizing warm sector.
Additional robust convection will likely develop Tuesday afternoon
farther south along the dryline over the Ozarks and Mid-South. A
favorable parameter space for supercells and all severe hazards
remains evident, with the threat for severe thunderstorms continuing
Tuesday afternoon/evening across parts of the OH Valley.

...Day 5/Wednesday...
Although some differences in model guidance regarding the upper-air
pattern across the central/eastern CONUS begin to emerge by
Wednesday, there is still good agreement that a belt of strong
mid-level flow will remain in place from the southern/central Plains
northeastward to the OH Valley and Great Lakes. It appears that
another embedded shortwave trough will advance eastward from the
southern/central Plains into the mid MS Valley by Wednesday evening.
A very moist and moderately to strongly unstable airmass should
reside to the east of a cold front/dryline across these regions,
potentially extending as far north into much of the Midwest/OH
Valley. Strong deep-layer shear will favor organized convection,
including supercells and bowing line segments posing a threat for
all severe hazards. Depending on the influence of prior convection,
the very favorable parameter space forecast for Wednesday across
parts of the southern Plains into the mid MS Valley and OH Valley
may necessitate greater severe probabilities in a later outlook.

...Day 6/Thursday...
Multiple days of robust and potentially widespread convection
complicates the severe potential for Thursday. Still, some severe
risk remains evident along/south of what will probably be a
convectively reinforced front/boundary extending across parts of the
southern Plains into the Southeast and Mid-Atlantic. It is possible
that one or more 15% severe areas for Thursday will be needed for
these regions given favorable forecast instability/shear. But, this
is still dependent on better agreement in model guidance regarding
the extent/placement of moderate to strong instability, and overall
convective coverage Thursday afternoon/evening.

...Day 7/Friday and Day 8/Saturday...
The spatial extent of the warm sector should tend to become more
confined late next week and into the weekend. There is a fair amount
of spread in model guidance regarding the strength and placement of
an upper trough/low over the eastern CONUS in this time frame.
Still, a severe risk may continue Friday along/south of a front that
should be in place over parts of the Southeast. Any lingering severe
threat into Saturday may be even farther south and confined to
mainly parts of FL.

..Gleason.. 05/04/2024

 

[Tempestas Tonitrua]

Lord have mercy.

Going to second that again

 

[KevinH]

Undoubtedly Monday and Tuesday both look to be quite significant wind- and hail-wise, thereby meriting attention for these alone. Re: Monday, I was only speaking about the dearth of top-tier tornado outbreaks over the south-central Plains for nearly a decade or so, which has been talked about by others, i.e., professional meteorologists, climatologists (Thomas P. Grazulis), and chasers. Even if truly historic events are infrequent, high-end, HIGH-Risk-worthy tornado outbreaks have historically tended to occur more frequently on a decadal basis regionally than we have seen since 2013 or so. I am just wondering as to when big tornado outbreaks will finally start to return to this part of the Plains. So I am asking: what are the odds that the Euro ensemble mean will swing toward a top-tier tornado scenario for Monday at this range?

Your word salads always amuse me lol

 

[jiharris0220]

It’s truly amazing the human ability to say so much and yet say absolutely nothing at all.

 

[KevinH]

It’s truly amazing the human ability to say so much and yet say absolutely nothing at all.

Right

 

[Tempestas Tonitrua]

It’s truly amazing the human ability to say so much and yet say absolutely nothing at all.

Good point. I may come across as harsh, but he has a long history of doing this and not in good faith. His posts are shrouded as him posing “questions”, but he’s actually attempting to push a personal agenda.

 

[cincywx]

CSU guidance seems very aggressive on a major 3 day severe weather outbreak:

View attachment 26288
View attachment 26289
View attachment 26290

Personally, there do seem to be multiple possible failure modes/limiting factors in terms of tornadoes, and right now I am not anticipating anything huge, although a high ceiling exists on all three days so its important to be very vigilant. However at least in terms of hail and wind, next week looks significant.

gotta dust this off for the third time this season:

 

[ZexityViking]

 

[KevinH]

Good point. I may come across as harsh, but he has a long history of doing this and not in good faith. His posts are shrouded as him posing “questions”, but he’s actually attempting to push a personal agenda.

Which is probably why he isn’t taken too seriously and/or ignored *shrug*

Anyway… back to our REGULARLY scheduled severe programming lol

 

[UK_EF4]

Undoubtedly Monday and Tuesday both look to be quite significant wind- and hail-wise, thereby meriting attention for these alone. Re: Monday, I was only speaking about the dearth of top-tier tornado outbreaks over the south-central Plains for nearly a decade or so, which has been talked about by others, i.e., professional meteorologists, climatologists (Thomas P. Grazulis), and chasers. Even if truly historic events are infrequent, high-end, HIGH-Risk-worthy tornado outbreaks have historically tended to occur more frequently on a decadal basis regionally than we have seen since 2013 or so. I am just wondering as to when big tornado outbreaks will finally start to return to this part of the Plains. So I am asking: what are the odds that the Euro ensemble mean will swing toward a top-tier tornado scenario for Monday at this range?

Of the Top 7 outbreaks with the highest 24 hour tornado counts, the 2020s alone have had more than any other decade - and we are just 4 years in - let that sink in. Sure you could make an argument for increased tornado detection 'inflating' counts - but then you also have had numerous long track, violent tornado disasters as part of these outbreaks in the last 10 years as well.

I do respect your opinion, and appreciate your dedication to finding obscure pieces of evidence and (sometimes near impossible to hit) criteria to back up your theory, but there seems to be a clear bias that is blindsiding you. Its no doubt that tornadic patterns will be/and already are changing as the climate shifts. But any indication that this reduces the number of significant outbreaks and violent tornadoes is *currently* incredibly murky, with little evidence to back it up: Outbreaks with multiple discrete supercells which produce multiple long tracked intense tornadoes have always been extremely rare, and always will be, and I'm genuinely curious what makes you think this isn't the case.

 

[Fred Gossage]

With respect to what constitutes a High Risk level outbreak, it is probabilistically driven completely these days, but from the system's inception in the early 80s up through at least the mid 2000s or later, the outlooks (while having probabilities publicly as early as the early 2000s), were still verified on a reports vs square mileage schematic. Under that verification system, per every 50,000 square miles (think roughly Oklahoma without the panhandle), a High Risk's criteria was met if 20 or more tornadoes occurred with a minimum of at least two of them having to be (E)F3 or higher intensity. Since the late 2000s, those outlooks stopped being verified on a hard reports vs aerial coverage schematic and were 100% driven in all aspects by the probabilistic contours. That makes verification a little more subjective. And in terms of issuing a High Risk outlook these days, SPC has gone on record publicly stating that they tend to try to focus on days when they specifically think violent tornadoes (EF4+) are an elevated concern, even though significant tornadoes overall is what is looked at for verification. With all that in mind, however, the system was designed so that those two verification methods wouldn't really clash with each other. That shows that it doesn't take something as widespread violent as a rare once-a-decade outbreak to verify a High Risk. Both April 26th and April 27th last week would've verified High Risk outlooks on their respective days with total tornado count over a regionally concentrated area coupled with number of those being EF3 or greater each day. That's not a hindsight 20/20 criticism of the SPC outlooks that were issued. Both days had question marks on them. However, in terms of verification itself, both days met High Risk criteria. It doesn't take a once-a-decade type outbreak to do that. We need to stop trying to pull talking points out of our intestinal tracts, please.....

 

[Tempestas Tonitrua]

You’re right about this. By no means do I “like” the controversy and ugliness that all this inevitably invites and dredges up again and again. I will admit, however, that the entire AGW issue, and the general blindness surrounding it, genuinely makes me angry at times…

As someone who once volunteered (not interned, I don’t want to exaggerate my role) for the Atlantic hurricane reanalysis project by utilising old newspaper microfiche and other historical sources, I am particularly attuned to this. If I come across as arrogant in some of my posts, it’s because I’m personally worn out and tired due to this singular issue that has consumed me.

All quotes taken Here.

I will admit that I am on a “crusade” here, but solely out of a sincerely held belief.

@UK_EF4 while I appreciate your willingness to try and debate, engage, and educate him, it’s not going to get very far. This isn’t a rational actor (saying this subject consumes him). He does this every tornado season and it’s on purpose as he says in the above posts.