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Severe WX April 1-2 (overnight) Severe Weather Event

DanLarsen34 said:
Taken at face value, that would depict the most significant event by aerial extent that we’ve seen since the March 31, 2023 outbreak.

We’ll see if these trends continue as we close in, but the signals are there right now for an incredibly high-ceiling event.

Just out of curiosity, what are the CIPS analogs pinging right now for comparable events?
Click to expand...
Screenshot_2025-03-29-19-18-29-68_40deb401b9ffe8e1df2f1cc5ba480b12.jpg
 
The setup next Wednesday continues to look pretty high-end, its not hard to see why the experts at the SPC have delineated a very large 30% area with the mention of 'several tornadoes'.

Very strong, broad-based trough overlapping a very large warm sector. I tried to draw the 60F DP line in black over the 500mb chart, and you can clearly see how the mid-level speed max is impinging on the northern half of the warm sector. While fairly basic, that alone is a fairly strong signal for a widespread severe weather risk

500wh.conus.jpg

The one thing that could be viewed as somewhat of a limiter is the fact the strongest synoptic scale forcing will be limited to the Upper Midwest and Great Lakes region, further north than the warm sector. In fact, most regions in the SPC 30% area see very small or even zero height falls throughout the forecast period, especially 21z-03z. This is likely to make initiation, especially from S IN into TN much more dependent on surface factors.

That being said, surface factors at the moment do seem to favor at least a scattered storm mode. Most model soundings suggest capping will be fairly minimal, and there also seems to be support for a confluence zone (rough position denoted with green dashed line) running from NE Arkansas up to wards IN/OH. This does seem to set the stage for dangerous event Wednesday afternoon/evening.

I don't make this comparison in terms of saying this event will be the same, whatsoever. However, 1974 had a similar situation in that height falls were fairly minimal through the southern portion of the risk area but mesoscale features led to the development of a couple convective bands. Read more in this paper here:

journals.ametsoc.org

Revisiting the 3â4 April 1974 Super Outbreak of Tornadoes

Abstract The Super Outbreak of tornadoes over the central and eastern United States on 3â4 April 1974 remains the most outstanding severe convective weather episode on record in the continental United States. The outbreak far surpassed previous and succeeding events in severity, longevity, and...
journals.ametsoc.org journals.ametsoc.org

To stress again, I am not in anyway comparing the events other than noting a lack of strong upper level forcing doesn't necessarily mean there wont be widespread severe. I am sure there are better examples than this, but I trust this forum is not as weenie as other places (cough wxtwitter) to take comparisons like this out of context anyway.

Either way, models should be watched closely next few days.
 
UK_EF4 said:
The setup next Wednesday continues to look pretty high-end, its not hard to see why the experts at the SPC have delineated a very large 30% area with the mention of 'several tornadoes'.

Very strong, broad-based trough overlapping a very large warm sector. I tried to draw the 60F DP line in black over the 500mb chart, and you can clearly see how the mid-level speed max is impinging on the northern half of the warm sector. While fairly basic, that alone is a fairly strong signal for a widespread severe weather risk

View attachment 37720

The one thing that could be viewed as somewhat of a limiter is the fact the strongest synoptic scale forcing will be limited to the Upper Midwest and Great Lakes region, further north than the warm sector. In fact, most regions in the SPC 30% area see very small or even zero height falls throughout the forecast period, especially 21z-03z. This is likely to make initiation, especially from S IN into TN much more dependent on surface factors.

That being said, surface factors at the moment do seem to favor at least a scattered storm mode. Most model soundings suggest capping will be fairly minimal, and there also seems to be support for a confluence zone (rough position denoted with green dashed line) running from NE Arkansas up to wards IN/OH. This does seem to set the stage for dangerous event Wednesday afternoon/evening.

I don't make this comparison in terms of saying this event will be the same, whatsoever. However, 1974 had a similar situation in that height falls were fairly minimal through the southern portion of the risk area but mesoscale features led to the development of a couple convective bands. Read more in this paper here:

journals.ametsoc.org

Revisiting the 3â4 April 1974 Super Outbreak of Tornadoes

Abstract The Super Outbreak of tornadoes over the central and eastern United States on 3â4 April 1974 remains the most outstanding severe convective weather episode on record in the continental United States. The outbreak far surpassed previous and succeeding events in severity, longevity, and...
journals.ametsoc.org journals.ametsoc.org

To stress again, I am not in anyway comparing the events other than noting a lack of strong upper level forcing doesn't necessarily mean there wont be widespread severe. I am sure there are better examples than this, but I trust this forum is not as weenie as other places (cough wxtwitter) to take comparisons like this out of context anyway.

Either way, models should be watched closely next few days.
Click to expand...
I would not rule out another slp developing further south …
 
tennessee storm chaser said:
I would not rule out another slp developing further south …
Click to expand...

Unless something fairly major changes in the forecast, I would say that a true secondary low is exceptionally unlikely.

1743331396103.png1743331461024.png

The jet pattern doesn't really indicate any synoptic scale ascent that would make that likely. On the right, note how the vorticity advection is almost entirely across the Upper Midwest where the main surface low will be.

A convectively induced secondary low would probably be the only way you would get an area of lower pressure in this setup, but the the implications of this on severe risk are different to a true secondary low (like the one on 4/27/2011). The models like the GFS which are showing small dips in the surface pressure are very likely just attempting to model deep convection.

All that being said, a secondary low pressure is not necessary in this case for a widespread severe risk.
 
UK_EF4 said:
.I don't make this comparison in terms of saying this event will be the same, whatsoever. However, 1974 had a similar situation in that height falls were fairly minimal through the southern portion of the risk area but mesoscale features led to the development of a couple convective bands. Read more in this paper here:
Click to expand...
This is an excellent write up @UK_EF4

I’ve read Corfidi’s paper countless times and you pretty much nailed it. What’s interesting is height falls were on the lower side as well on the northern end, per Trey’s analysis, even with the main jet starting to impinge on that area. Convective Band 2 supercells, which were the primary violent tornado producer, formed 200 miles east of the actual synoptic dryline. So you had very deep OWS initiation due to as you said, finer mesoscale mechanisms.

What’s very interesting is I read a recent paper by Tony Lyza on the characteristics and formation areas of supercells on 4/27/11 that I’ll link below. On 4/27/11, Twelve supercells that initiated were in the vicinity of a remnant thermal boundary zone left by the first two QLCSs. So because of those two precursor rounds, you had an additional 12 supercells able to form due to a mix of outflow and mesoscale interactions.

Guess what other event had a morning MCS plow through the main threat area merely hours before the main event? 4/3/1974. Which I am sure the outflow left behind from that MCS led to additional supercells forming, just like on 4/27/11. The only difference was, in a few cases on 4/27/11, the northern outflow cells ran right northeast off the boundary and in 50 miles they were right into that cooler rain shield up into Tennessee. On 4/3/74 there were no rain shields anywhere near initiation, so those additional outflow cells were able to continue deep into the warm sector.

All this is to say, it takes some mesoscale black magic and optimal alignment with the Synoptics to produce a very high end outbreak. With mesoscale and storm scale so hard to resolve on models, you really don’t know how ultra high a ceiling of an event is until it’s occurring.

 
UK_EF4 said:
The setup next Wednesday continues to look pretty high-end, its not hard to see why the experts at the SPC have delineated a very large 30% area with the mention of 'several tornadoes'.

Very strong, broad-based trough overlapping a very large warm sector. I tried to draw the 60F DP line in black over the 500mb chart, and you can clearly see how the mid-level speed max is impinging on the northern half of the warm sector. While fairly basic, that alone is a fairly strong signal for a widespread severe weather risk

View attachment 37720

The one thing that could be viewed as somewhat of a limiter is the fact the strongest synoptic scale forcing will be limited to the Upper Midwest and Great Lakes region, further north than the warm sector. In fact, most regions in the SPC 30% area see very small or even zero height falls throughout the forecast period, especially 21z-03z. This is likely to make initiation, especially from S IN into TN much more dependent on surface factors.

That being said, surface factors at the moment do seem to favor at least a scattered storm mode. Most model soundings suggest capping will be fairly minimal, and there also seems to be support for a confluence zone (rough position denoted with green dashed line) running from NE Arkansas up to wards IN/OH. This does seem to set the stage for dangerous event Wednesday afternoon/evening.

I don't make this comparison in terms of saying this event will be the same, whatsoever. However, 1974 had a similar situation in that height falls were fairly minimal through the southern portion of the risk area but mesoscale features led to the development of a couple convective bands. Read more in this paper here:

journals.ametsoc.org

Revisiting the 3â4 April 1974 Super Outbreak of Tornadoes

Abstract The Super Outbreak of tornadoes over the central and eastern United States on 3â4 April 1974 remains the most outstanding severe convective weather episode on record in the continental United States. The outbreak far surpassed previous and succeeding events in severity, longevity, and...
journals.ametsoc.org journals.ametsoc.org

To stress again, I am not in anyway comparing the events other than noting a lack of strong upper level forcing doesn't necessarily mean there wont be widespread severe. I am sure there are better examples than this, but I trust this forum is not as weenie as other places (cough wxtwitter) to take comparisons like this out of context anyway.

Either way, models should be watched closely next few days.
Click to expand...
spc states that the main storm mode is supercells
 
CheeselandSkies said:
So NAM is now in range for Wednesday afternoon as of today's 12Z run. I pulled two soundings off the northern extent of the risk area (northern Illinois) one valid for 18Z (1 PM) and the other 21Z (4 PM) and found it amusing that the analogs on each were both from BMX, but different events.

View attachment 37734View attachment 37735
Click to expand...
Yikes. I see a cold season analog with spring thermodynamics..
 
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