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

[Kds86z]

Yes, that’s a good point. I think both Friday and Yesterday were highly cyclic. The strong shear meant the mid level mesocyclones were obviously strong but I noticed the RFDs were often quite unstable, in some cases positioned behind the FFD of the supercell which resulted in numerous tornadoes, each strong, from most of the supercells. As opposed to a day like 12/10 where your supercells were extremely stable and long tracked. The observed sound from LIX at 18z yesterday in fact was very plains like I thought, with the classic sickle shape.

Would’ve been worse obviously if we had a lot of long trackers and faster storm motions.

 

[Telstar]

Storms starting to pop southwest of Nashville

It really has to be a challenge deciding whether the model has lost touch or the dynamics have changed. And I would venture to say the best route on that front is better safe than sorry.

Friday was certainly the most impressive- at least in my eyes and on the storm report scoreboard (if there is such a thing). On Wednesday, if you had told me that I would have been surprised.

I am honestly wondering if 4/27 and a few of the other major outbreaks have adjusted (unrealistically) the ceiling for many. Similar to becoming an Alabama fan in the late 2000’s, your expectations are always national championship or else. Maybe it’s on US (professionals/enthusiast/and general public) to readjust our expectations for what a high end risk looks like. I think most of us have to be honest with ourselves and even if we don’t vocally state the comparison, it’s hard to not use that as a benchmark.

I think this is spot on. Whenever we get a high-risk day, I can’t help but remember 4/27. High risk and 4/27 have become linked. But I still want the SPC to call it like they see it. Better to err on the side of caution and be thankful it wasn’t worse than it was.

 

[Kds86z]

Except there was that pesky whatever-it-was (general consensus seems to be a series of destructive mergers) that prevented that long-track supercell across central Illinois from a significant tornado-producer. And the excessive forcing in the northern mode that made the Keota cell essentially a one-off in terms of cyclic tornadic supercells.

We like to say nature doesn't have a calendar and a "generational" outbreak can happen any time, but there's a reason they're as rare as they are. Everything has to go absolutely perfect for a setup to go as completely off the chains as those two did.

Yeah I always tell friends who aren’t as familiar, just how absolutely perfect it has to be more strong and especially violent tornadoes, let alone significant outbreaks.

 

[jiharris0220]

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.

 

[Kds86z]

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 mid 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 and 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.

Thanks for this @jiharris0220, but what about that spread of temperature and dewpoints? Should be high LCL.

 

[GA Stormchaser]

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.

I’m also well overdue for this. Thanks for the nudge.

 

[jiharris0220]

Thanks for this @jiharris0220, but what about that spread of temperature and dewpoints? Should be high LCL.

The dew points yesterday were in the mid to high 60s, low 70s, with temperatures in the high 60s to 70s, with no drying at all up until the EML.

LCL doesn’t really matter, although they would’ve been higher had more surface heating occurred.

Remember how unusually high the cloud bases were for 4/27? I remember a lot of discussion on how unique it was for a Dixie alley event.

 

[UK_EF4]

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 mid 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.

I also think your mesoscale issue become a lot less important with extremely high end synoptic setups. If yesterday’s trough had ejected even just a few hours later, and a tad to the north, we would have easily seen the most significant Dixie outbreak since 2011. Once the trends in the trough commenced to be slower and More meridional and we had that lead shortwave which really developed some of the early day convection it looked clear a 45% level outbreak was not on the cards.

Even then, with plenty of strong tornadoes, and probably a couple violent intensity tornadoes, this outbreak clearly verified the High Risk and will remembered as possibly the most significant of the year.

 

[Kds86z]

The dew points yesterday were in the mid to high 60s, low 70s, with temperatures in the high 60s to 70s, with no drying at all up until the EML.

LCL doesn’t really matter, although they would’ve been higher had more surface heating occurred.

Remember how unusually high the cloud bases were for 4/27? I remember a lot of discussion on how unique it was for a Dixie alley event.

Yeah you got my attention with 4/27 I meant. Usually you need very low lcl for violent tornadoes. I am stunned…

 

[Tomcats Forever!]

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 mid 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.

What does PBL mean?

 

[Kds86z]

What does PBL mean?

Planetary boundary layer

 

[jiharris0220]

I also think your mesoscale issue become a lot less important with extremely high end synoptic setups. If yesterday’s trough had ejected even just a few hours later, and a tad to the north, we would have easily seen the most significant Dixie outbreak since 2011. Once the trends in the trough commenced to be slower and More meridional and we had that lead shortwave which really developed some of the early day convection it looked clear a 45% level outbreak was not on the cards.

Even then, with plenty of strong tornadoes, and probably a couple violent intensity tornadoes, this outbreak clearly verified the High Risk and will remembered as possibly the most significant of the year.

Maybe, but looking at the soundings between the two outbreaks, there really wasn’t much difference until you looked at the PBL and it becomes obvious what caped yesterday.

Surface mixing would’ve made it too dry for crapvection to form, and looking at how yesterday evolved it’s also clear had it not been for that, we would’ve had many more tornadoes, as well as long tracked ones.

Not saying at all that there weren’t minor synoptic setbacks though.

 

[tornado examiner]

QRT definitely coming in for this one. Impressive damage indeed.

 

[jiharris0220]

Speaking of which, here are the practically perfect obs for the march 14th outbreak. Obviously more reports need to come in but so far it actually looks like moderate risk was the right call for now.

 

[Kds86z]

Speaking of which, here are the practically perfect obs for the march 14th outbreak. Obviously more reports need to come in but so far it actually looks like moderate risk was the right call for now.
View attachment 36492

Wow. Yes indeed . They were spot on also, saying multiple long lived intense tornadoes. @UK_EF4 also was right with detailed forecast hours before. Classic supercell outbreak.

 

[jiharris0220]

And here are the soundings regarding both outbreaks in the afternoon hours for context. Thanks to @ColdFront for providing these.

 

[jiharris0220]

 

[CheeselandSkies]

The dew points yesterday were in the mid to high 60s, low 70s, with temperatures in the high 60s to 70s, with no drying at all up until the EML.

LCL doesn’t really matter, although they would’ve been higher had more surface heating occurred.

Remember how unusually high the cloud bases were for 4/27? I remember a lot of discussion on how unique it was for a Dixie alley event.

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.

 

[ColdFront]

And here are the soundings regarding both outbreaks in the afternoon hours for context. Thanks to @ColdFront for providing these.

I actually didn’t notice this yesterday when I looked at the soundings, but yesterday had more MLCAPE than the special BMX sounding. And a full 2 hours before. 2018 vs 2196.

For reference, here is BMX at 00Z that day.



Cap is completely eroded, the lower levels are a tad saturated but not nearly to the point of yesterday. The event was already well underway and the EML had done its job and the warm sector was still clean of anything but tornadic supercells over Alabama.

 

[AJS]

Assuming construction was good, EF4 is definitely on the table Contextual damage seems pretty intense.