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Severe WX Severe Weather Threat 3/14-3/16

Bulkshear said:
This one also correlates with a TNI above 2! You also have this storm happening in the correct phase too, well this only matters if you think ENSO heavily dictates major outbreaks.
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Like said take that gfs run face value for now .look for SPC have rather large area 30 percent shade for Friday . If euro Ukie and ensembles are correct
 
Justin Hindman said:
I look at these models, but it’s all blank to me until it’s 24-48 hours out. Last three systems have been big hyped . This one does looks the strongest so far I will say
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For weenies, good strategy to avoid chaser heartbreak. For general public, the need to be aware is self-evident.
 
Just out of sheer curiosity, of the event which we shall speak not of, do we have any good model data archived from 5-7 days ahead of the event? It'd be interesting to compare. NOT saying this is similar, but let's be honest, that event is the benchmark we kinda-sorta have to compare all others against these days.
 
wx_guy said:
Just out of sheer curiosity, of the event which we shall speak not of, do we have any good model data archived from 5-7 days ahead of the event? It'd be interesting to compare. NOT saying this is similar, but let's be honest, that event is the benchmark we kinda-sorta have to compare all others against these days.
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There is plenty of data in the 4/27 thread on this site
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Archive - Severe threat April 26-27, 2011

This thread is a real-time re-creation of the April 27, 2011 event thread. Posts in this thread will be made at the same date and time as the original thread in 2011. Replies will not be allowed in this thread, instead we ask that you use the April 27, 2011 discussion thread instead...
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I know a few of my posts today have referenced both 4/3/74 and 4/27/11. Not to absolutely compare them to what could possibly occur this weekend. My point is to really highlight not every set up has to be extremely perfect and pristine with zero possible fail modes to yield a big outbreak.

4/3/74 had a massive MCS roll through the day of. Actually closer in timeframe to the main event than the nighttime QLCS on 4/27/11. That could’ve absolutely hampered instability. If winds hadn’t channeled correctly to induce confluence in the Mississippi River Valley we may have not had convective band 2 on 4/3/74. Parts of Alabama stayed stormy All day on 4/27/11 (Northwest Alabama and Northeast Alabama) and hadn’t recovered atmospherically like the central part of the state, that didn’t stop the Hackleburg tornado or The two Jackson county EF4s later. those possible fail modes just didn’t matter.

You can have a slam dunk model set up (5/20/2019) that craps out, or a major outbreak that looks marginal at first (thinking of 4/26/2024).

Edit: for reference, convective band 2 was responsible for the vast majority of violent tornados on 4/3/74. Those supercells actually initiated 200 miles east of the dryline.
 
This is from Chat GPT so please...take it with grains of salt! That being said, it's very obvious AI is making leaps and bounds and can interpret this sounding pretty effectively. This is its response to my box sounding encompassing all of eastern MS and all of western AL at 21z on Saturday. Thoughts?



This box sounding from the 18z GFS valid for Saturday (March 15, 21z) over eastern Mississippi and western Alabama suggests a highly volatile severe weather environment with strong tornado potential.

Thermodynamics:​

  • MLCAPE: ~1700 J/kg, with SBCAPE slightly higher at ~1900 J/kg. These values indicate moderate instability, sufficient for sustained deep convection.
  • LCL (Lifted Condensation Level): ~745m AGL – very low, suggesting strong low-level buoyancy and efficient stretching of updrafts.
  • LFC (Level of Free Convection): ~1.1 km – also quite low, which supports quick storm development and low CINH.
  • EL (Equilibrium Level): ~12.5 km, meaning strong updrafts will have room to grow deep into the troposphere.
  • Steep lapse rates: The 700-500mb lapse rate is 7.0°C/km, which is favorable for robust convection.

Kinematics (Shear & Hodograph Analysis):​

  • 0-1km SRH: 517 m²/s² and 0-3km SRH: 597 m²/s² – These values are highly supportive of tornadic supercells, especially in a low LCL environment.
  • Bulk shear:
    • 0-6km shear: ~80 knots – extremely strong, ensuring strong storm organization.
    • Effective inflow shear: 64 knots – indicating supercell support.
  • Critical Angle: 56° – Favorable for effective streamwise vorticity ingestion.
  • Hodograph: Displays a large, curved shape in the lowest 1-3 km, with substantial veering and elongation – highly favorable for tornado development.

Significant Tornado Potential:​

  • Supercell Composite Parameter (SCP): 16.6 – very high, strongly supportive of discrete supercells.
  • Significant Tornado Parameter (STP):
    • Effective-layer STP: 3.6 (without CIN) and 1.1 (with CIN). This is supportive of strong tornadoes, though CINH may need to erode for storm initiation.
  • SARS Analog Matches:
    • 77% match to a past violent tornado case (TOR PDS)
    • 50% significant hail match
  • PDS Tornado Threat Classification – This highlights the strong risk of EF2+ tornadoes given convective initiation.

Storm Mode & Hazards:​

  • Storm motions: Right-moving supercells expected with a 220°/55kt mean vector – fast-moving storms.
  • Low-Level Shear (LLS): ~200 m²/s² – highly supportive of tornadogenesis.
  • EBWD (Effective Bulk Wind Difference): 64 knots, reinforcing the supercell threat.

Conclusion:​

This box sounding strongly suggests a dangerous severe weather event with the potential for significant, long-track tornadoes. If convection initiates and remains discrete, any storm developing in this environment will likely become tornadic quickly. The combination of low LCLs, extreme low-level shear, and strong instability makes this a classic high-end tornadic setup for the Deep South. If this forecast holds, this would warrant a moderate or higher risk outlook from SPC.
 
ColdFront said:
I know a few of my posts today have referenced both 4/3/74 and 4/27/11. Not to absolutely compare them to what could possibly occur this weekend. My point is to really highlight not every set up has to be extremely perfect and pristine with zero possible fail modes to yield a big outbreak.

4/3/74 had a massive MCS roll through the day of. Actually closer in timeframe to the main event than the nighttime QLCS on 4/27/11. That could’ve absolutely hampered instability. If winds hadn’t channeled correctly to induce confluence in the Mississippi River Valley we may have not had convective band 2 on 4/3/74. Parts of Alabama stayed stormy All day on 4/27/11 (Northwest Alabama and Northeast Alabama) and hadn’t recovered atmospherically like the central part of the state, that didn’t stop the Hackleburg tornado or The two Jackson county EF4s later. those possible fail modes just didn’t matter.

You can have a slam dunk model set up (5/20/2019) that craps out, or a major outbreak that looks marginal at first (thinking of 4/26/2024).

Edit: for reference, convective band 2 was responsible for the vast majority of violent tornados on 4/3/74. Those supercells actually initiated 200 miles east of the dryline.
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Yep, extremely important to highlight that even some of our classic example outbreaks weren't 100% magically perfect setups in every sense, and you certainly don't need any such thing to get a deadly and prolific outbreak.
 
wx_guy said:
This is from Chat GPT so please...take it with grains of salt! That being said, it's very obvious AI is making leaps and bounds and can interpret this sounding pretty effectively. This is its response to my box sounding encompassing all of eastern MS and all of western AL at 21z on Saturday. Thoughts?



This box sounding from the 18z GFS valid for Saturday (March 15, 21z) over eastern Mississippi and western Alabama suggests a highly volatile severe weather environment with strong tornado potential.

Thermodynamics:​

  • MLCAPE: ~1700 J/kg, with SBCAPE slightly higher at ~1900 J/kg. These values indicate moderate instability, sufficient for sustained deep convection.
  • LCL (Lifted Condensation Level): ~745m AGL – very low, suggesting strong low-level buoyancy and efficient stretching of updrafts.
  • LFC (Level of Free Convection): ~1.1 km – also quite low, which supports quick storm development and low CINH.
  • EL (Equilibrium Level): ~12.5 km, meaning strong updrafts will have room to grow deep into the troposphere.
  • Steep lapse rates: The 700-500mb lapse rate is 7.0°C/km, which is favorable for robust convection.

Kinematics (Shear & Hodograph Analysis):​

  • 0-1km SRH: 517 m²/s² and 0-3km SRH: 597 m²/s² – These values are highly supportive of tornadic supercells, especially in a low LCL environment.
  • Bulk shear:
    • 0-6km shear: ~80 knots – extremely strong, ensuring strong storm organization.
    • Effective inflow shear: 64 knots – indicating supercell support.
  • Critical Angle: 56° – Favorable for effective streamwise vorticity ingestion.
  • Hodograph: Displays a large, curved shape in the lowest 1-3 km, with substantial veering and elongation – highly favorable for tornado development.

Significant Tornado Potential:​

  • Supercell Composite Parameter (SCP): 16.6 – very high, strongly supportive of discrete supercells.
  • Significant Tornado Parameter (STP):
    • Effective-layer STP: 3.6 (without CIN) and 1.1 (with CIN). This is supportive of strong tornadoes, though CINH may need to erode for storm initiation.
  • SARS Analog Matches:
    • 77% match to a past violent tornado case (TOR PDS)
    • 50% significant hail match
  • PDS Tornado Threat Classification – This highlights the strong risk of EF2+ tornadoes given convective initiation.

Storm Mode & Hazards:​

  • Storm motions: Right-moving supercells expected with a 220°/55kt mean vector – fast-moving storms.
  • Low-Level Shear (LLS): ~200 m²/s² – highly supportive of tornadogenesis.
  • EBWD (Effective Bulk Wind Difference): 64 knots, reinforcing the supercell threat.

Conclusion:​

This box sounding strongly suggests a dangerous severe weather event with the potential for significant, long-track tornadoes. If convection initiates and remains discrete, any storm developing in this environment will likely become tornadic quickly. The combination of low LCLs, extreme low-level shear, and strong instability makes this a classic high-end tornadic setup for the Deep South. If this forecast holds, this would warrant a moderate or higher risk outlook from SPC.
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That's wild that chatGPT basically breaks down soundings.
 
UncleJuJu98 said:
That's wild that chatGPT basically breaks down soundings.
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Yes, it's definitely gotten much better in the past year or so! I gave it a sounding last severe weather season in the spring and it made lots of mistakes. This time it's pretty accurate and explains things very well.
 
Clancy said:
Yep, extremely important to highlight that even some of our classic example outbreaks weren't 100% magically perfect setups in every sense, and you certainly don't need any such thing to get a deadly and prolific outbreak.
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100%

On the AmericanWX forum there were already people saying the crapvection rolling through Alabama in the early morning hours would hamper the outbreak. Our gold standard outbreaks all had fail modes and flies in the ointment the day of. They just pushed them aside.
 
UncleJuJu98 said:
Can you ask it what the fail modes of this event could be?
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Sure


Despite the highly favorable parameters in this sounding, there are several potential failure modes that could limit this event from becoming a full-fledged outbreak. Here are the main avenues of failure:

1. Capping and Lack of Initiation (CI Failure)​

  • CIN (Convective Inhibition): While relatively weak (-13 J/kg), there is still some CINH present. If large-scale ascent (e.g., a shortwave trough or surface forcing) does not adequately overcome this, storms may struggle to initiate.
  • Weak Mid-Level Cooling: If mid-level temperatures remain too warm (i.e., EML influence), inhibition could persist longer than expected, delaying or preventing storm development.

2. Early or Widespread Convection Leading to Messy Storm Mode​

  • Too Many Storms / Upscale Growth: If convection initiates too early or in too many places, storms could quickly merge into a linear system (QLCS), reducing the potential for long-track supercells.
  • Cold Pool Interactions: If early convection generates strong cold pools, it could undercut inflow and disrupt the environment before peak instability is realized.
  • Storm Interference: Given high storm-relative helicity (SRH), storms will be competing for low-level vorticity. If too many storms develop in proximity, they may disrupt each other's inflow.

3. Veered Surface Winds / Suboptimal Low-Level Hodograph​

  • Surface Winds Not Backing Enough: The hodograph is already large and curved, but if surface winds veer too much (e.g., shift to SW too early), it could reduce low-level SRH and negatively impact tornado potential.
  • Critical Angle Shift: The current 56° critical angle is sufficient for effective inflow, but if it tightens (e.g., drops to <30°), storms may struggle to ingest streamwise vorticity efficiently.

4. Poor Timing of Key Ingredients​

  • Upper-Level Forcing Misalignment: If the best synoptic ascent arrives too late (e.g., after peak diurnal heating), storms may not fully realize their potential.
  • Dewpoint Mixing / Boundary Layer Drying: If drier air entrains into the warm sector or mixing lowers dewpoints (currently low-to-mid 60s°F, but ideally should stay higher), instability could be reduced.

5. Excessive Storm Motion & Outrun of Low-Level Instability​

  • Very Fast Storm Speeds (~55 knots): Storms moving too quickly may struggle to remain in the most unstable air for long enough.
  • Displacement of Low-Level CAPE (3CAPE = 28 J/kg): If storms outpace low-level instability, tornadogenesis could be limited.

Bottom Line​

The biggest failure mode would likely stem from either too little storm coverage (CI failure) or too much (messy storm mode/QCLS evolution). The current parameters strongly favor supercells and tornadoes, but subtle shifts in low-level wind profiles, surface moisture, or convective evolution could dramatically alter the outcome.
 
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