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

UK_EF4 said:
Friday now really starting to look like a very widespread severe weather day too - moisture has trended upwards on the NAM in the last few runs, likely both because it's catching up on its cooler bias and also a possible hint that the wave today isn't as damaging to moisture return as thought (note the trend from SE to S surface winds). The globals haven't quite caught on to this trend yet but by tomorrow morning, if we do see a proper shift, things will likely be clear by then as tonight's severe threat will have passed.

Regardless, as the mid-upper level cold pool starts to impinge on the warm sector from MO/IL up into IA, expect rapid development of powerful supercellular thunderstorms which quickly develop into a QLCS with embedded mesocyclones. Current simulated reflectivity from the models indicate an arced band of storms pretty much following the boundary of the cold pool in red which would make plenty of sense. Would be a pretty notable large hail risk, especially into Iowa where low level shear is a little weaker and those 500mb temps are coldest.

View attachment 35186View attachment 35187

Tornado threat seems fairly uncertain mainly due to questions about storm mode and surface moisture quality. Too much dry air at the surface could over strengthen downdrafts early on, though I'm wondering if due to the strength of the storm relative inflow this may be balanced somewhat. By about 00z though, moisture depth improves and given the wind shear - which looks to be perpendicular to the line of storms, especially across E/NE MO, we could see an environment extremely supportive of long tracked, potentially strong, QLCS circulations and embedded mesocyclones. I honestly think for a maximized tornado risk you might want storms close to or within the line of storms as opposed to completely discrete, which would limit the effect of wind shear ripping updrafts apart.

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Greatest threat will almost undoubtedly be the wind threat though. Whilst obviously not the same, the positioning of that jet core literally right behind the line of storms almost acts as a synoptic scale RIJ, and especially when the boundary layer is drier early on your downdrafts are going to massively accelerate as they hit towards the ground and become very powerful. We honestly could have a full on derecho from MO into IL which is probably quite uncommon for this time of year.

There is then the more uncertain southern mode, which the SPC seems fairly bullish on so definitely needs close watching. Quality moisture will be in place from E AR into TN/MS by around 00z, spreading up into W KY by around 03z and wind profiles look just as favorable for long tracked, strong supercells. Obviously dont take STP too literally but I overlayed the rough position of the jet core at 500mb onto the STP map and that zone from NE AR into W KY and W TN certainly makes me nervous for a nocturnal intense tornado threat. Will need to see what kind of CAM signal develops for this area but already a fairly concerning look from the NAM.

View attachment 35198

All in all, a very significant one for Friday too. Some of the previous trends reducing the impact certainly seem to be slightly retreating but all I can think is thank god we had today's shortwave across the south otherwise we would have been in for an absolutely wild ride on Friday too. Could easily see the SPC going moderate as early as the first D2 outlook. Some aspects of the setup look reminiscent of some pretty high-end severe scenarios (northern mode especially has some hints of 12/15/21 and 3/31/23. Don't want to rush in completely at this point but if the current trends continue Friday-Saturday might unfortunately be one to remember.
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See easily. 15 hatched tornado threat being issued . Unfortunately do think the tornado threat is going up Friday. Latest trends
 
Speaking of the communications issues from 4/27 (which impacted me greatly that day), I just received a T-Mobile text message 45 minutes ago saying the satellite texting beta from Starlink was just activated on my phone.

Hopefully, it isn't something I'll ever have to use. Reason I'm bringing this up is that I believe other carriers have satellite messaging available nowadays. Anyone in a threat area should probably consider checking availability of satellite messaging with their carrier. Better to be safe than sorry.
 
Julian said:
Why is a broad based trough more conducive for tornados?
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Subtle forcing. It’s actually a delicate balance. You want enough forcing to get a few storms up and going but not enough to swamp the warm sector. While it may seem counterintuitive, too much forcing and you may get storms to go up, but they’ll quickly congeal into a line.

4/27/11 was so subtly forced that even the trailing dry line didn’t have a huge line of storms on it.
 
ColdFront said:
Subtle forcing. It’s actually a delicate balance. You want enough forcing to get a few storms up and going but not enough to swamp the warm sector. While it may seem counterintuitive, too much forcing and you may get storms to go up, but they’ll quickly congeal into a line.

4/27/11 was so subtly forced that even the trailing dry line didn’t have a huge line of storms on it.
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Thanks! I thought it had something to do with storm mode or expanse of the warm sector.
 
UK_EF4 said:
Greatest threat will almost undoubtedly be the wind threat though. Whilst obviously not the same, the positioning of that jet core literally right behind the line of storms almost acts as a synoptic scale RIJ, and especially when the boundary layer is drier early on your downdrafts are going to massively accelerate as they hit towards the ground and become very powerful. We honestly could have a full on derecho from MO into IL which is probably quite uncommon for this time of year.
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I agree with this, I could see a derecho/strong qlcs tornado threat out of this at a minimum
 
ColdFront said:
Subtle forcing. It’s actually a delicate balance. You want enough forcing to get a few storms up and going but not enough to swamp the warm sector. While it may seem counterintuitive, too much forcing and you may get storms to go up, but they’ll quickly congeal into a line.

4/27/11 was so subtly forced that even the trailing dry line didn’t have a huge line of storms on it.
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I’m addition to more subtle forcing, broader trough bases tend to lead to deep layer shear vectors that are more oblique to the main synoptic boundary. This tends to delay any upscale growth and keeps convective mode more discrete or semi-descrete. Convective mode is always finicky to forecast.
 
This sounding for 21z on Saturday off the 18z NAM is near the LA/MS stateline in eastern LA. To say it's bonkers is an understatement.


1741818408149.png


To those interested in my statistical journey in this, I applied the distance algorithm I developed yesterday against the SARS database that's used in the SHARPPY soundings on Pivotal Weather, Tropical Tidbits, SPC's website, and most other places. (By the way!!!! The soundings only go up to 2004 in the database, so the 4/27/11 CANT show up as an analog on it. In case you were wondering.)

Here are the Top 10 analogs to that sounding. 80% tornadic, 40% EF2+. And that's considering that 20% of this database is EF2+ tornadoes (technically F2 because it was before the EF scale). So that's high!

Of course, it doesn't take a statistical algorithm to show that the sounding above, painted in so much magenta, is bad news.




1741818373962.png
 
GA Stormchaser said:
I’m sure you know this, but I post this to just clarify to new folks…and to give the newbies the perspective of why folks in the Southeast are so sensitive to this day. “Several people died” equates to “324 people died”
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Just so people understand the gravity, 324 would be 10% of total (both sides) killed in action in the bloodiest single day of US combat, at Antietam.
 
Here is a large box sounding from the 18z NAM that encompasses all of central and eastern MS and all of western AL (seeing a pattern here?). I asked ChatGPT to give an unbiased, somewhat technical, and frank public message concerning this. Its output is below. It's not mincing words.

1741819204170.png





Severe Weather Analysis and Forecast – March 15, 2025​

Synoptic Overview & Sounding Analysis:
The provided NAM forecast sounding for 21Z on March 15, 2025, captures a large domain across central/eastern Mississippi and western Alabama, encompassing a highly sheared, strongly unstable pre-convective environment conducive to tornadic supercells.

Thermodynamics:

  • MLCAPE: 1,758 J/kg – Sufficient for robust updrafts, especially with deep-layer shear in place.
  • 3CAPE: 91 J/kg – Favorable for near-ground stretching, enhancing tornado potential.
  • SFC Temperature / Dewpoint: 67°F-70°F / ~60°F – Warm, moist boundary layer supporting buoyant parcels.
  • LCL / LFC Heights: 655m / 1,140m – Very low LCLs favor tornadogenesis, particularly in high-shear regimes.
  • Mid-Level Lapse Rates: 7.7°C/km – Moderately steep, indicating strong mid-level cooling aloft.
  • PWAT: 1.51” – Ample moisture for sustained convection.
  • DCAPE: 800 J/kg – Sufficient for strong downdraft potential, suggesting a risk for damaging RFD surges.
Kinematics:

  • 0-1km Shear: 35 kt
  • 0-1km SRH: 355 m²/s² – Strongly supportive of low-level mesocyclones.
  • 0-3km SRH: 444 m²/s² – Further indicative of robust streamwise vorticity ingestion.
  • 0-6km Shear: 78 kt – Easily supports organized supercells with strong mid-level rotation.
  • Critical Angle: 55° – Favorable for streamwise vorticity ingestion and efficient tornadogenesis.
Supercell Composite & STP (Significant Tornado Parameter):

  • Supercell Composite: 15.6 – Strongly indicative of long-lived supercells.
  • STP (fixed): 4.2 – High-end values associated with significant tornadoes.
  • Effective Layer STP: Probability of EF2+ tornadoes at ~0.25-0.32, indicating a marked potential for strong tornadoes.
Analog Guidance:

  • The SARS dataset indicates a 67% match to past significant tornado outbreaks, further reinforcing the risk for violent tornadoes.

Forecast & Public Discussion: <EDIT: THIS IS NOT REAL, IT'S CHAT GPT SIMULATED MSG!!!>​

…SEVERE WEATHER OUTBREAK EXPECTED ACROSS THE DEEP SOUTH ON SATURDAY…
…POTENTIALLY LONG-TRACK TORNADOES POSSIBLE…

An extremely volatile environment will be in place across central/eastern Mississippi and western Alabama on Saturday, March 15. Forecast soundings depict a classic high-shear, high-CAPE setup with a strongly veering wind profile, deep low-level moisture, and very favorable tornado-supportive hodographs.

Thunderstorms will initiate along a surface boundary by mid-afternoon and quickly become discrete supercells, given 80+ kt deep-layer shear. Given 0-1km SRH exceeding 350-400 m²/s², multiple strong to violent tornadoes (EF2-EF4+) appear possible, particularly in the vicinity of the I-20 corridor.

Public Call to Action:
Residents in the highlighted region must have a severe weather plan in place. These types of setups are rare and can produce deadly tornadoes, particularly after dark. Ensure you have multiple ways to receive warnings, and be prepared to shelter immediately if a tornado warning is issued for your area. The combination of instability, moisture, and shear suggests that a high-end tornado outbreak is a distinct possibility.

Stay tuned for updates from the SPC, NWS, and local meteorologists. This is a life-threatening situation.
 
wx_guy said:
Here is a large box sounding from the 18z NAM that encompasses all of central and eastern MS and all of western AL (seeing a pattern here?). I asked ChatGPT to give an unbiased, somewhat technical, and frank public message concerning this. Its output is below. It's not mincing words.

View attachment 35216





Severe Weather Analysis and Forecast – March 15, 2025​

Synoptic Overview & Sounding Analysis:
The provided NAM forecast sounding for 21Z on March 15, 2025, captures a large domain across central/eastern Mississippi and western Alabama, encompassing a highly sheared, strongly unstable pre-convective environment conducive to tornadic supercells.

Thermodynamics:

  • MLCAPE: 1,758 J/kg – Sufficient for robust updrafts, especially with deep-layer shear in place.
  • 3CAPE: 91 J/kg – Favorable for near-ground stretching, enhancing tornado potential.
  • SFC Temperature / Dewpoint: 67°F-70°F / ~60°F – Warm, moist boundary layer supporting buoyant parcels.
  • LCL / LFC Heights: 655m / 1,140m – Very low LCLs favor tornadogenesis, particularly in high-shear regimes.
  • Mid-Level Lapse Rates: 7.7°C/km – Moderately steep, indicating strong mid-level cooling aloft.
  • PWAT: 1.51” – Ample moisture for sustained convection.
  • DCAPE: 800 J/kg – Sufficient for strong downdraft potential, suggesting a risk for damaging RFD surges.
Kinematics:

  • 0-1km Shear: 35 kt
  • 0-1km SRH: 355 m²/s² – Strongly supportive of low-level mesocyclones.
  • 0-3km SRH: 444 m²/s² – Further indicative of robust streamwise vorticity ingestion.
  • 0-6km Shear: 78 kt – Easily supports organized supercells with strong mid-level rotation.
  • Critical Angle: 55° – Favorable for streamwise vorticity ingestion and efficient tornadogenesis.
Supercell Composite & STP (Significant Tornado Parameter):

  • Supercell Composite: 15.6 – Strongly indicative of long-lived supercells.
  • STP (fixed): 4.2 – High-end values associated with significant tornadoes.
  • Effective Layer STP: Probability of EF2+ tornadoes at ~0.25-0.32, indicating a marked potential for strong tornadoes.
Analog Guidance:

  • The SARS dataset indicates a 67% match to past significant tornado outbreaks, further reinforcing the risk for violent tornadoes.

Forecast & Public Discussion:​

…SEVERE WEATHER OUTBREAK EXPECTED ACROSS THE DEEP SOUTH ON SATURDAY…
…POTENTIALLY LONG-TRACK TORNADOES POSSIBLE…

An extremely volatile environment will be in place across central/eastern Mississippi and western Alabama on Saturday, March 15. Forecast soundings depict a classic high-shear, high-CAPE setup with a strongly veering wind profile, deep low-level moisture, and very favorable tornado-supportive hodographs.

Thunderstorms will initiate along a surface boundary by mid-afternoon and quickly become discrete supercells, given 80+ kt deep-layer shear. Given 0-1km SRH exceeding 350-400 m²/s², multiple strong to violent tornadoes (EF2-EF4+) appear possible, particularly in the vicinity of the I-20 corridor.

Public Call to Action:
Residents in the highlighted region must have a severe weather plan in place. These types of setups are rare and can produce deadly tornadoes, particularly after dark. Ensure you have multiple ways to receive warnings, and be prepared to shelter immediately if a tornado warning is issued for your area. The combination of instability, moisture, and shear suggests that a high-end tornado outbreak is a distinct possibility.

Stay tuned for updates from the SPC, NWS, and local meteorologists. This is a life-threatening situation.
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wow
 
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