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

jiharris0220 said:
What prevented yesterday from becoming a super outbreak is that the PBL was too saturated, and believe it or not, that’s really the only major thing that held it back.

Sure, we can nit pick the wave guide and jet streak timing, but those were minor imperfections.

The over saturated PBL caused a huge precip shield to incase the individual supercells, pretty much constantly chocking them out; which led to overall less tornado spam than expected.

This is why the supercells that managed to over come this (which was impressive enough) simply could not sustain a long track tornado, as rain cooled air swiftly cut off inflow.

If you compared soundings with yesterdays and the 4/27 outbreak, the only things 4/27 had over yesterday was slightly better thermos, (3500-4000j/kg cape and LLLR of 8+C/km). Of course, upper/mid level jet stream had a longer wave guide and more perpendicular orientation as well; which made it easier for storms to bunker right.

But by far the most important aspect was the difference in vertical profiles in the PBL. 4/27 had surface temps in the low to mid 80s and dew points in the low to high 60s, a bit “dry”. This all but denied stratus form precip or shallow convection to form within the confluence bands, which allowed supercells to produce long track tornadoes.

Remember the storm mode yesterday, and you guys will notice something. And it’s that yesterday’s storm mode was indeed semi to completely discrete, as the supercells yesterday after the initial 3 hours into the event were clearly spaced out and weren’t embedded in a squall line.

Instead of full fledged thunderstorms interfering with them, it was just a bunch of strato form precip, 4/27 would’ve ended up like that (along with the other minor synoptic/mesoscale factors) if weren’t for the surface mixing that occurred at midday.

Again, I want everyone to understand just how scarily close yesterday came to being a super outbreak. A little more surface mixing, better waveguide structure and jet streak placement was the glass plain that slowed down the bullet, “only” leaving a modest wound, instead of gaping whole in the torso.
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This is awesome. Thank you for a really nice explanation. That’s exactly what I was looking for when I asked my original question earlier this AM.
 
CheeselandSkies said:
Some of the 4/27 supercells had really odd/interesting structures. The updraft bases were really dramatically carved out with huge, widely visible tornado cyclones/wall clouds, but the bases of those themselves were quite low, leading to the actual tornadoes appearing as rather stubby cylinders/wedges. Of course there were exceptions, such as the tall stovepipe/multi-vortex early stages of the Cullman tornado.
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Honestly with yesterday’s outbreak and looking at back at 4/27, I think we actually have a substantial lead on what makes or breaks a super outbreak.

4/27 was an anomaly regarding the highly visible tornadoes and high cloud bases.

Apparently, this anomaly was actually the one major ingredient we overlooked despite it staring us in the face.

Look at the two soundings again, and notice the LFC is far higher in altitude than yesterday’s event, and it’s obvious that was due to the surface mixing.

It’s actually quite substantial looking at it, no wonder crapvection was utterly non existent.

I always wondered why there were none, I mean sure there was a cap and weak forcing but I always thought it was weird how there simply wasn’t any precip in between the supercells that day. It’s literally Dixie alley, yet the low levels were behaving like central plains setups.

Well, now I know why.
 
CheeselandSkies said:
Some of the 4/27 supercells had really odd/interesting structures. The updraft bases were really dramatically carved out with huge, widely visible tornado cyclones/wall clouds, but the bases of those themselves were quite low, leading to the actual tornadoes appearing as rather stubby cylinders/wedges. Of course there were exceptions, such as the tall stovepipe/multi-vortex early stages of the Cullman tornado.
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That’s a really good point because there’s a study I’ve read with pictures showing that once the Cullman tornado crossed the rain cooled boundary from the midday MCS, it actually lowered into more of a stubby wedge shape as the LCLs dropped lower.

The Hackleburg tornado when it was well north of thermal boundary when it was caught on tv cameras was also scraping the ground, I believe the temp/dew was something like 66/65 at that stage. Here is a RAP proximity sounding for the Hackleburg/Smithville tornados that day:

1742142208116.png

Those cells were pretty jam packed in that little area of NE MS and NW AL.

That wind profile should be in a museum
 
I am very excited to see how much/how fast AI learning improves forecasting and catching these types of variables. Just look at medicine… AI is finding pathways to solutions doctors and scientists have worked on for years. And it’s not the they are poorly-trained, ignorant, or stupid- but rather some of these problems are complex and multifaceted such as two unique weather sequences utilizing / affecting the same kinetic resources on back to back days.
 
ColdFront said:
That’s a really good point because there’s a study I’ve read with pictures showing that once the Cullman tornado crossed the rain cooled boundary from the midday MCS, it actually lowered into more of a stubby wedge shape as the LCLs dropped lower.

The Hackleburg tornado when it was well north of thermal boundary when it was caught on tv cameras was also scraping the ground, I believe the temp/dew was something like 66/65 at that stage. Here is a RAP proximity sounding for the Hackleburg/Smithville tornados that day:

View attachment 36496

Those cells were pretty jam packed in that little area of NE MS and NW AL.

That wind profile should be in a museum
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I remember that black low hackleburg for sure.
 
All in all, I think we can identify the 6 main ingredients for a super outbreak.

1. Longwave trough

2. Perpendicular orientation of the jet streak over PBL flow

3. Modest forcing

4. A decent amount of surface mixing (drying of low levels) to prevent crapvection

5. Moist mid levels

6. Extreme kinematics

Getting all 5 of these to occur at the same time is why these sorts of outbreaks only happen every 30+ years.
 
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Blountwolf said:
Seconded - and those of you who I see ALL the time in here <cough cough> have very little excuse to not be sustaining members. Cheaper than going to Starbucks once a month.
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GA Stormchaser said:
I’m also well overdue for this. Thanks for the nudge.
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I was also well overdue to do this. I've been on this forum for a long time, at least 2011. It has taught me much and kept me updated on many situations.
 
I’m working on a side hobby project of collecting proximity soundings using RAP and Python for all the major tornados on 4/27/11 that I think will be very interesting.

On the topic of super outbreak soundings, specifically 4/3/74 here is MGM(Montgomery) at 12Z. Monster loaded gun with a lot of dry air a loft. The atmosphere was already primed.

1742143032246.gif
And later at 0Z:
1742143073599.gif


Similar look for BNA (Nashville) at 12Z:
1742143124482.gif

Dayton at 12Z and 0Z:

1742143290165.png


1742143317835.png
 
ColdFront said:
I’m working on a side hobby project of collecting proximity soundings using RAP and Python for all the major tornados on 4/27/11 that I think will be very interesting.

On the topic of super outbreak soundings, specifically 4/3/74 here is MGM(Montgomery) at 12Z. Monster loaded gun with a lot of dry air a loft. The atmosphere was already primed.

View attachment 36497
And later at 0Z:
View attachment 36498


Similar look for BNA (Nashville) at 12Z:
View attachment 36499

Dayton at 12Z and 0Z:

View attachment 36500


View attachment 36501
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All of these soundings contain a decent amount of mixing in the low levels, which would explain why cloud bases for the 1974 super outbreak were also a bit elevated and no crapvection.
 
jiharris0220 said:
Honestly with yesterday’s outbreak and looking at back at 4/27, I think we actually have a substantial lead on what makes or breaks a super outbreak.

4/27 was an anomaly regarding the highly visible tornadoes and high cloud bases.

Apparently, this anomaly was actually the one major ingredient we overlooked despite it staring us in the face.

Look at the two soundings again, and notice the LFC is far higher in altitude than yesterday’s event, and it’s obvious that was due to the surface mixing.

It’s actually quite substantial looking at it, no wonder crapvection was utterly non existent.

I always wondered why there were none, I mean sure there was a cap and weak forcing but I always thought it was weird how there simply wasn’t any precip in between the supercells that day. It’s literally Dixie alley, yet the low levels were behaving like central plains setups.

Well, now I know why.
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Very interesting. I wonder if there are soundings available from '74 and Palm Sunday '65 that support this

Edit: well I already have my answer on 74.
 
Tomcats Forever! said:
Very interesting. I wonder if there are soundings available from '74 and Palm Sunday '65 that support thos
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Look at what @ColdFront just posted above, very similar soundings to 4/27, particularly the mixing occurring in the low levels that we have been discussing.

But now I’m wondering if 1965 Palm Sunday also has similar soundings.
 
jiharris0220 said:
Look at what @ColdFront just posted above, very similar soundings to 4/27, particularly the mixing occurring in the low levels that we have been discussing.

But now I’m wondering if 1965 Palm Sunday also has similar soundings.
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I have seen soundings from Palm Sunday, let me see if I can find them. The instability wasn’t on the super outbreak level, but the actual kinematics were extremely on the high end, and probably surpassed the super outbreaks in certain spots. You had deep bulk shear in excess of 100 KTs in places
 
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