Severe WX April 11th-13th, 2020 Severe Weather Threat

[brianc33710]

OK. I can't get several quotes to post so I won't post any. I won't say that Sunday will be "a Forecasted Convective Amplification Deficiency." I think that we will have a significant severe weather outbreak tomorrow. I just question that significance. Will it be a once-a-year event or once-a-decade event? That's all. At worst, I will go with what I said last night, a 15 April 2011 event w/ the EF-4-5 thrown into the mix from 08 April 1998 outbreak.

Edit -- for what its worth, I have bookmarked that 27 April 2011 PDS Tornado Watch 235. Here is that link.

 

[bwalk]

Let's hope not, Tuscaloosa & Bham!

12Z Saturday high Res NAM model shows an STP(Significant Tornado Parameter) as high as 16.3 near Tuscaloosa at 11PM Sunday night.. It got up to around 13 on 4/27/11. All of the blue area is over 10, which is sky high.



[ref: weather nerds Alabama]

 

[MattPetrulli]

Can we stop posting pretty colors in reference to strong tornadoes? Convective evolution and mode is gonna make or break this, not the pretty colors.

 

[Parysa]

OK. I can't get several quotes to post so I won't post any. I won't say that Sunday will be "a Forecasted Convective Amplification Deficiency." I think that we will have a significant severe weather outbreak tomorrow. I just question that significance. Will it be a once-a-year event or once-a-decade event? That's all. At worst, I will go with what I said last night, a 15 April 2011 event w/ the EF-4-5 thrown into the mix from 08 April 1998 outbreak.

Edit -- for what its worth, I have bookmarked that 27 April 2011 PDS Tornado Watch 235. Here is that link.

4/15/11 was still a record-breaking day. It just got forgotten somewhat bc of 4/27.

 

[Kory]

Can we stop posting pretty colors in reference to strong tornadoes? Convective evolution and mode is gonna make or break this, not the pretty colors.

STP won’t matter as much if this vort max kicks out and fires off too much convection leading to a squall line and too much convection over the warm sector.

That is my biggest hang up right now. Too much forcing from the shortwave kicking out and then things gets all linear with cell interactions. But it’s not surface temps, nor dew point, nor too much capping.

 

[darkskys25]

Trust me, there is plenty enough forcing for convection across the warm sector as it pivots negative tilt in the afternoon...and that’s not a concern mentioned at all unless I missed it in the SPC discussion. The question the SPC explicitly states is when/where the elevated morning complex become surface based with the 60-70 kt LLJ begins bringing in higher dews and we get surface destabilization. They are trying to resolve where that southern edge from the morning complex of storms races across TN/MS/AL as that will determine the extent of the warm sector.

Calling potential Forecasted Convective Amplification Deficiency a day out might be a new record.

SPC: The extent of
development within the warm sector remains somewhat uncertain, given
the presence of a capping inversion and generally subtle foci for
initiation.
SPC:
While the conditional risk of all severe hazards will be quite high
if supercells develop

Note: "conditional risk"

They didnt say when supercells develop they said "if"

Im just saying that i agree there are uncertanties. And of course tomorrow can Forecasted Convective Amplification Deficiency. It was but just two weeks ago everyone was talking about the epic outbreak in Illinois. That was a Forecasted Convective Amplification Deficiency and it looked epic the day before. We have big busts every year. We had a quite a few this year here in dixie alley if you believed the euro 3 to 4 days out. Just ask Reed Timer. How many times has he called for an outbreak this year. We have all experienced it many times and will continue to see busts. I was just stating that there are uncertanties and so was SPC. But like I said prior to my last line this has big potential for sig severe wx tomorrow no doubt. But the uncertanties give me pause. Apparently SPC feels the same way.

 

[brianc33710]

Let's hope not, Tuscaloosa & Bham!

12Z Saturday high Res NAM model shows an STP(Significant Tornado Parameter) as high as 16.3 near Tuscaloosa at 11PM Sunday night.. It got up to around 13 on 4/27/11. All of the blue area is over 10, which is sky high.

View attachment 2750

[ref: weather nerds Alabama]

While I want to avoid mentioning that April 2011 superoutbreak as much as possible, I will bring up a couple of things from James Spann's & James Simpson interactions from that day. When that rain shower developed a tornado signature in just 10 min, Spann showed the details. At that time, both thought that the STP maxed out at 10. All of a sudden the STP pops up at a 12.6, and they're briefly without words lol. I remember seeing a 17.5 STP that night, 5 or more 15+, and a dozen STPs > 10.

 

[jmills]

Composite parameters like STP, SCP, EHI and others are great for first glance situational awareness but they all make significant assumptions and say nothing regarding convective mode, evolution, and they gloss over some of the finer points of the thermodynamic and kinematic profiles.

Don’t get too caught up in them. Just take them as indicators of a background environment that is supportive of significant severe weather. But that assumes storms form in that environment and convective mode/convective mode plays along nicely.

 

[darkskys25]

Taking the current DPs/Temps and saying "the models are wrong about what's going to happen because of what's happening now" still a full day out just seems irresponsible. We won't know much from surface obs until at least tomorrow morning as it'll give us a better idea of which models are handling this event better.

I dont know of any model that had us destabilizing tonight. The dews come crashing in tomorrow quickly! There is some uncertainty how far north that gets advected.

 

[Stormchaser4life]

Cams definitely showing a very complex and possible messy evolution tomorrow. Lead shortwaves ahead of the main disturbance can really wreak havoc on models. 18z hrrr continues to show widespread storms into the afternoon with really no period of a lull. This could hold warm sector further south and possibly impact low level cape/lapse rates. The evolution of this early day activity will determine how volatile the main event will be. Definitely not looking as clear as a few days ago

 

[MichelleH]

While I want to avoid mentioning that April 2011 superoutbreak as much as possible, I will bring up a couple of things from James Spann's & James Samsons interactions from that day. When that rain shower developed a tornado signature in just 10 min, Spann showed the details. At that time, both thought that the STP maxed out at 10. All of a sudden the STP pops up at a 12.6, and they're briefly without words lol. I remember seeing a 17.5 STP that night, 5 or more 15+, and a dozen STPs > 10.

Jason Simpson

 

[Kory]

SPC: The extent of
development within the warm sector remains somewhat uncertain, given
the presence of a capping inversion and generally subtle foci for
initiation.
SPC:
While the conditional risk of all severe hazards will be quite high
if supercells develop

Note: "conditional risk"

They didnt say when supercells develop they said "if"

Im just saying that i agree there are uncertanties. And of course tomorrow can Forecasted Convective Amplification Deficiency. It was but just two weeks ago everyone was talking about the epic outbreak in Illinois. That was a Forecasted Convective Amplification Deficiency and it looked epic the day before. We have big busts every year. We had a quite a few this year here in dixie alley if you believed the euro 3 to 4 days out. Just ask Reed Timer. How many times has he called for an outbreak this year. We have all experienced it many times and will continue to see busts. I was just stating that there are uncertanties and so was SPC. But like I said prior to my last line this has big potential for sig severe wx tomorrow no doubt. But the uncertanties give me pause. Apparently SPC feels the same way.

Reed Timmer is irrelevant here and I’m not sure why you’re bringing him up. As I just stated, I think the only hang up here is TOO much forcing leading to a lot of cell interaction and quicker than anticipated transition to linear storm mode.

 

[brianc33710]

4/15/11 was still a record-breaking day. It just got forgotten somewhat bc of 4/27.

Yeah. The only thing that 15 April 2011 outbreak lacked was a violent EF-4/5 tornado. Not to forget, the AM 27 April 2011 outbreak was huge too, with EF-3s. That knocked out power which dramatically increased the death toll from that afternoon thru early AM 28 April. March 1994, April 1998, April 2010, March 2019, and other outbreaks had the violent twisters but not as many overall tornadoes.

 

[brianc33710]

Jason Simpson

Fixed! Thank you!

 

[bwalk]

Can we stop posting pretty colors in reference to strong tornadoes? Convective evolution and mode is gonna make or break this, not the pretty colors.

So MattMexs: Are you saying you don't see any value in the STP - especially when the numbers are as remarkable as they are with this system? Are you saying the STP should be ignored in a moderate outbreak situation? I'm just trying to respectfully figure out your aversion to graphs with color in them & you telling people not to post graphs on this board.

 

[bwalk]

UKMET hodo for Sunday night 00z (7 pm). Critical value has jumped from Day 3 in the 40s to Day 2 at 75. Critical value could approach the sweetspot 90 degree range by Day 1 (or not).




Notice: There are no "pretty colors" in this graph.

 

[South AL Wx]

BMX afternoon AFD is a good write-up about the complexity of the forecast:

/Regional severe weather event with high-impact potential
expected on Sunday; some intricate elements becoming evident,
making for complex forecast/

At sunrise Sunday, a lead shortwave, having aided in some early day
showers & elevated storms across northern areas, will be moving
toward Southern Appalachia. Additional impulses emanating from the
southwesterly flow aloft, preceding the primary/potent trough,
will play crucial roles in the weather setup for the rest of the
event. Through the morning & afternoon, unstable air will advect
northward immediately behind the warm front. Guidance still shows
the warm front moving far enough north to include all of Central
Alabama within a plume of upper 60s to near 70 (F) dew points.
Very strong dynamics & wind shear will also arrive at a swift
pace. Surface winds will be breezy/gusty outside of any
thunderstorms. A wind advisory will be in effect.

Guidance is triggering convection associated with a follow-up
impulse aloft arriving around midday. Some of this activity would be
north of the instability axis, while some would be involved within
the unstable side of the warm front. Given the background parameters
in place, any convection favoring the warm side could become severe
with all hazards.

Through the afternoon & evening, dynamics & wind shear increase
further as the upper trough takes on a negative tilt. Strong
southerly advection will supply us with moderate SB-CAPE. Mid-level
lapse rates are expected to be around 6.5 to 7 C/km. 1km/3km SRH
will be high given backed surface flow & large, curved hodographs.
Convection (already severe) arriving from the west will pose a
threat of tornadoes, damaging winds, and large hail. Corridors of
enhanced threats could evolve, yielding a strong/long-track
tornado potential as well as swaths of damaging straight-line
winds. These would result from discrete supercells, line-embedded
supercells, and bowing structures. Considering earlier convection,
surface boundaries could come into play.

Could there be a drawback? Sure, considering the `waves` of
convection as well as development & evolution characteristics/mode
of the primary wave (late afternoon/evening). Even so, the overall
setup is highly supportive of widespread severe weather. Analogs
are implying a prominent area from the ArkLaMiss to Central
Alabama. This is in line with the higher severe probabilities.

 

[xJownage]

So MattMexs: Are you saying you don't see any value in the STP - especially when the numbers are as remarkable as they are with this system? Are you saying the STP should be ignored in a moderate outbreak situation? I'm just trying to respectfully figure out your aversion to graphs with color in them & you telling people not to post graphs on this board.

His point seems to be that the STP with this system isn't going to make a huge difference on whether the system pans out as violent or not, and that storm modes and other factors are more likely to determine what we see.

 

[MattPetrulli]

So MattMexs: Are you saying you don't see any value in the STP - especially when the numbers are as remarkable as they are with this system? Are you saying the STP should be ignored in a moderate outbreak situation? I'm just trying to respectfully figure out your aversion to graphs with color in them & you telling people not to post graphs on this board.

Jownage gets it, those parameters aren't gonna be mean much when its all messy and destructive storm mode. STP, EHI, SCP, etc isn't gonna determine much in this setup when the main issue here is obviously storm mode and convective evolution.

 

[bwalk]

His point seems to be that the STP with this system isn't going to make a huge difference on whether the system pans out as violent or not, and that storm modes and other factors are more likely to determine what we see.

His point seems to be that the STP with this system isn't going to make a huge difference on whether the system pans out as violent or not, and that storm modes and other factors are more likely to determine what we see.

Thanks, XJownage. The issue to me is censorship in a public forum. Do we need to choose a committee to analyze each system and decide what information is relevant and what is not for that particular system and then only allow committee-deemed relevant information to be posted?

I just posted info about the hodos for tomorrow's system. Now I feel like I have done something "wrong" in doing so.