April 12 Severe Event

[joshwx2003]

Latest Euro model run shows the set up to be almost exactly like April 27th 2011. The deep low (992mb) is forecast to move just south of St Louis, along with a neutral/negative tilted trough. 

PDS soundings are now screaming all over the south for Sunday.

[jojo762]

12Z Euro continues to depict potential for a high-end severe weather event on Sunday April 12 across mostly Mississippi, Alabama, and Tennessee.

100-110kt 500mb jet streak atop a 60-70kt LLJ, juxtaposed to 67-71 degree dewpoints and steep lapse rates leading to CAPE values on the order of 2000-4000 j/kg. Insane.

12Z GFS is about 9 to 12 hours faster than the ECMWF, leading to a significantly lessened severe threat.

If the last few runs of the Euro were to verify, we would be dealing with a historic tornado outbreak, if the GFS verifies we will probably be dealing with a lower-end severe threat. 

[joshwx2003]

1 hour ago, jojo762 said:

12Z Euro continues to depict potential for a high-end severe weather event on Sunday April 12 across mostly Mississippi, Alabama, and Tennessee.

100-110kt 500mb jet streak atop a 60-70kt LLJ, juxtaposed to 67-71 degree dewpoints and steep lapse rates leading to CAPE values on the order of 2000-4000 j/kg. Insane.

12Z GFS is about 9 to 12 hours faster than the ECMWF, leading to a significantly lessened severe threat.

If the last few runs of the Euro were to verify, we would be dealing with a historic tornado outbreak, if the GFS verifies we will probably be dealing with a lower-end severe threat. 

Which model do you think is more accurate?

[jojo762]

1 hour ago, joshwx2003 said:

Which model do you think is more accurate?

Euro almost always wins in these situations, as the GFS is usually too fast with systems east of the Rockies... that being said, that doesn’t mean that the exact conditions the euro currently shows are going to come to fruition. It’s still in the “model lala land” range. 

[andyhb]

There's more to a "historic" tornado outbreak than just parameters. My biggest concern as of now is early convection mitigating the threat, especially if the warm front has more difficulty lifting north than forecast.

UK and Euro are consistent in a fairly ominous solution, but they also were for 3/28.

[jojo762]

1 hour ago, andyhb said:

There's more to a "historic" tornado outbreak than just parameters. My biggest concern as of now is early convection mitigating the threat, especially if the warm front has more difficulty lifting north than forecast.

UK and Euro are consistent in a fairly ominous solution, but they also were for 3/28.

Hmmm... Euro seemingly shows this, when looking at morning/early afternoon QPF; but vectors and storm motions seem to indicate that any junky early stuff *could* lift north of the warm front, negating any deleterious impact to the warm sector. I definitely agree with the potential problem of how far north the warm front can retreat, especially with a possible morning MCS and/or plenty of elevated convection.

Taking the Euro verbatim -- that would be a historic outbreak. Parameters aside, synoptic-scale (what's important at Day 6) specs on the euro are currently better than most outbreaks in that region. Doubt that it holds serve as is, especially given that this wave basically didn't exist a few runs ago, but we'll see.

[Macintosh]

4 hours ago, andyhb said:

There's more to a "historic" tornado outbreak than just parameters. My biggest concern as of now is early convection mitigating the threat, especially if the warm front has more difficulty lifting north than forecast.

UK and Euro are consistent in a fairly ominous solution, but they also were for 3/28.

April 27, 2011 through Huntsville AL... significant morning severe activity over the same areas did nothing to negate the afternoon activity. Wish it had. 
 

 

 

 

 

[StormySquares]

It depends on how prolonged the convection is. Much of Tennesee didn't destabilize on 4/27/11 because of prolonged convection. Had it, then the threat area could of reached further north then it did. 

[hlcater]

Definitely worried about sloppy storm modes for this one. Models(particularly the UK) have somewhat improved here, but there continues to be a signal for widespread thunderstorm activity potentially as early as 12z. Ideally, I'd like to put some distance between the setup and the gulf, or otherwise put something over the gulf/gulf coast(like the right exit region or an EML or both!) to temper the amount of thunderstorm activity we have. I'm not entirely sure there's much that can be done about tstm activity north of the warm front, or that it particularly matters in this setup if it clears out in a timely fashion. I think the ceiling is super high here given the frankly excessive hodographs that are present on the UK/Euro, IF we can get supercells in that environment. Even if we cant, a parameter space like that has a tendency to just make tornadoes out of blobs of rain.

[joshwx2003]

This is what we've been waiting for! The GFS has FINALLY almost mirrored the ECMWF's trend regarding a possible severe thunderstorm outbreak this coming Sunday across the Gulf Coast states. Both models show incredible dynamics & sufficient CAPE. This is it!

[Bob's Burgers]

12z NAM would suggest a High Risk is coming

[Sydney Claridge]

36 minutes ago, Bob's Burgers said:

12z NAM would suggest a High Risk is coming

That would be a very scary situation anywhere from Louisiana to Alabama, but particularly across northern Mississippi, if that run verifies.  I still have some questions about the extent of precipitation, but with the level of shear and helicity depicted, any area of warm-sector precipitation could be at risk of turning supercellular and tornadic.  This NAM run also shows an area of precipitation ahead of the main line (that is at the western edge of the 70F+ dewpoints) in E Mississippi and SE Louisiana, and I have little doubt that those storms could also turn tornadic.

Let's just hope that any tornadoes avoid highly-populated areas.  Given the COVID-19 pandemic, people that lose homes will need places to stay in the aftermath of a tornado, so they do not risk contracting COVID-19 (or contribute to its spread if they already have the virus); this is much more manageable if the tornadoes can stick to rural areas and avoid population centers, unfortunately the South is more densely populated than the Plains, so the odds are higher that a population center could get hit.  Hospitals are already burdened in some places by COVID-19 (particularly around New Orleans, though the worst of the severe weather should stay north of there), and the U.S. South is at particular risk of people developing serious complications, given that more people living there have preexisting medical conditions such as heart disease and diabetes.  Having a major tornado outbreak occur amongst this pandemic is one of my worst fears, especially should at least one of those tornadoes strike a major population center.  Needless to say I am hoping that this busts completely, but there could be a tornado outbreak this Sunday.

[jojo762]

46 minutes ago, BrandonC_TX said:

That would be a very scary situation anywhere from Louisiana to Alabama, but particularly across northern Mississippi, if that run verifies.  I still have some questions about the extent of precipitation, but with the level of shear and helicity depicted, any area of warm-sector precipitation could be at risk of turning supercellular and tornadic.  This NAM run also shows an area of precipitation ahead of the main line (that is at the western edge of the 70F+ dewpoints) in E Mississippi and SE Louisiana, and I have little doubt that those storms could also turn tornadic.

The "precipitation ahead of the main line" you're referencing would almost certainly be the main show, with several tornadic supercells in the open warm-sector associated with a pre-frontal trough -- consistent with outbreaks in Dixie Alley.

Also, looks like the 12z GFS has mostly came on board with the rest of the models with respect to potential for a dangerous severe weather outbreak, still some important differences though, especially with instability in the warm sector.

Not that it exactly matters, but would anticipate a rare Day 3 MDT risk encompassing large parts of Louisiana, Mississippi, and Alabama tomorrow.

My knowledge of southeast tornado environments is fairly lackluster, but something of concern to me is a similar looking thermodynamic environment to 5/20/19 in Oklahoma, and storms really struggled that day to get going in spite of amazing shear... Perhaps someone more knowledgeable could chime in?

[Sydney Claridge]

28 minutes ago, jojo762 said:

The "precipitation ahead of the main line" you're referencing would almost certainly be the main show, with several tornadic supercells in the open warm-sector associated with a pre-frontal trough -- consistent with outbreaks in Dixie Alley.

Sounds about right.  That line near the Mississippi River would probably go linear, but I doubt you could rule out tornadic supercells there either if that 12z NAM run is correct (with higher EHI in that area), and even if linear, QLCS tornadoes and embedded supercells could pose a danger.  But the most violent activity would have to be with any supercells ahead of this line.

[DanLarsen34]

One thing that jumps out to me in the model runs right now is that instability, though sufficient for an outbreak of tornadoes, isn’t off the charts. That’s one distinct difference from the 4-27 comparison that was tossed out there. 
 

The speed and directional shear, however, is highly concerning. Will be interesting to see how things play out over the next couple of model runs. 

[Bob's Burgers]

17 minutes ago, DanLarsen34 said:

One thing that jumps out to me in the model runs right now is that instability, though sufficient for an outbreak of tornadoes, isn’t off the charts. That’s one distinct difference from the 4-27 comparison that was tossed out there. 
 

The speed and directional shear, however, is highly concerning. Will be interesting to see how things play out over the next couple of model runs. 

Yep. You'd have to add about 1,200 j/kg ML cape to get to april 27 levels. Shear is there though. Modeled afternoon temps in the low 80's is very concerning though, especially the UKmet.

[Bob's Burgers]

13 minutes ago, Bob's Burgers said:

Yep. You'd have to add about 1,200 j/kg ML cape to get to april 27 levels. Shear is there though. Modeled afternoon temps in the low 80's is very concerning though, especially the UKmet.

12z Euro now on board with 80+ temps across LA, MS. Very bad scenario unfolding here.

[ILMRoss]

Stating the obvious, extremely high ceiling with this event. The 'best case' scenario is forcing coalescing the warm sector into a 'mega-squall', where you have one of those days that rack up 1000+ wind reports and a smattering of EF0-EF1 spin-ups on the line. 

A baked in source of good news is that on Easter Sunday, a shining candidate for our first high risk of the year, stay-at-home orders due to COVID-19 will make it much easier to communicate to people what's going on. 

[bdgwx]

The globals (GFS, UKMET, and ECMWF) have the high risk style look to them. And there's already a 60 contour showing up on the SREF tornado ingredients product. That's pretty high for the FH81 frame. There's not a whole of lot data to constrain this event at this point in time. 

I'm usually pretty conservative when guessing at the risk outlooks...sometimes too much so...but yeah, if tonight's global runs are not materially different than today then I too would not be surprised by a D3 moderate from the SPC tomorrow.

[joshwx2003]

20 minutes ago, bdgwx said:

The globals (GFS, UKMET, and ECMWF) have the high risk style look to them. And there's already a 60 contour showing up on the SREF tornado ingredients product. That's pretty high for the FH81 frame. There's not a whole of lot data to constrain this event at this point in time. 

I'm usually pretty conservative when guessing at the risk outlooks...sometimes too much so...but yeah, if tonight's global runs are not materially different than today then I too would not be surprised by a D3 moderate from the SPC tomorrow.

It might sound like a dumb question but why can’t they issue a Day 3 High Risk

[Calderon]

5 minutes ago, joshwx2003 said:

It might sound like a dumb question but why can’t they issue a Day 3 High Risk

They're just never done and operationally are impossible to issue.

[jojo762]

2 minutes ago, Calderon said:

They're just never done and operationally are impossible to issue.

Also, from a practical standpoint they just do not make sense. Too many things can happen between D3 to D1 to be sounding the alarms that much.

[DanLarsen34]

22 minutes ago, jojo762 said:

Also, from a practical standpoint they just do not make sense. Too many things can happen between D3 to D1 to be sounding the alarms that much.

Exactly. The language in the outlook can adequately convey the level of the potential threat that far out without having to issue a high risk. Moderates are rare enough as it is for Day 3. 

[Bob's Burgers]

16 minutes ago, DanLarsen34 said:

Exactly. The language in the outlook can adequately convey the level of the potential threat that far out without having to issue a high risk. Moderates are rare enough as it is for Day 3. 

^This. You can tell it's pretty clear from the SPC Convective Outlook that at least one upgrade is coming. Rare to see "Outbreak" mentioned in a D4, let alone a headline with 3 more subsequent uses.  While it's ENH for now, it's worded like a high-end moderate risk. 

[StormySquares]

It could be possible for a day 2 high risk. I doubt it with this event, but it has happened. Twice I think, 2006 and 2012.

[MattPetrulli]

Unless 00z guidance tanks, I think we will be seeing a day 3 moderate. Pretty good model agreement on a major threat for Sunday, however we have definitely seen threats like these fall apart within 3 days so lets not take an outbreak as a 100% certainty despite what some FB posters may say.

[Buddy1987]

23 minutes ago, MattPetrulli said:

Unless 00z guidance tanks, I think we will be seeing a day 3 moderate. Pretty good model agreement on a major threat for Sunday, however we have definitely seen threats like these fall apart within 3 days so lets not take an outbreak as a 100% certainty despite what some FB posters may say.

Kind of just starting to acclimate myself to this threat, as Blacksburg has somewhat kept it tepid. Do the ingredients get as far north as VA or is it more NC,SC and the Deep South on this one? 

[crossbowftw3]

31 minutes ago, StormySquares said:

It could be possible for a day 2 high risk. I doubt it with this event, but it has happened. Twice I think, 2006 and 2012.

4/7/06 and 4/14/12

[StormySquares]

2 minutes ago, crossbowftw3 said:

4/7/06 and 4/14/12

4/7/06 was also the only 60 sig tornado risk. I wonder if we would see that ever again. 

[Buddy1987]

More I look now more the parameters are the highest I’ve seen in some time for 0-1 helicity being 450-500 on the NAM and winds ripping right above the surface over 60 knots based on the GFS. Temps get close to 70. Question for the pros would be are we looking more at high shear low instability environment or do we have a chance to build up anything before everything comes together.