April 12 Severe Threat

[StormySquares]

Still some details to work out but severe weather may be returning to the valley this Weekend

[nrgjeff]

Euro doubled down for Sunday this afternoon (12Z Wednesday) with even more turning with height. However it's not all that warm Sunday. GFS continues to insist the WF gets hung up in the Deep South on widespread rain. Either way it's not ideal weather for an egg hunt.

[PowellVolz]

Euro doubled down for Sunday this afternoon (12Z Wednesday) with even more turning with height. However it's not all that warm Sunday. GFS continues to insist the WF gets hung up in the Deep South on widespread rain. Either way it's not ideal weather for an egg hunt.

I noticed temps are mid/upper 60’s for Sunday but you wonder if the mods are having issues with return flow this far out?


.

[nrgjeff]

Yes models are definitely struggling. Lots of WF rain would anchor the WF. However it's a robust neutral/negatively tilted system which can push WFs around. Models keep it cool. Yet their QPF swaths hint beasts moving from southwest to northeast. Note they did that a couple times last year, and it turned out non-severe rain with thunder; so, it's not set.

One thing upstairs the turning with height is at or greater than 45 deg. That can sometimes push precipitation off boundary triggers. If it were to close up to say, 30 deg, might have a better shot at a rain-out less severe.

I will say that this is no 4/27. That day turning was nearly 90 degrees; and, a true dry line punched through Dixie. It was like a Plains outbreak. Not happening Easter. 

My bearish lean is for our Region only! Deep South could have a nasty day closer to the Gulf Coast. Still no 4/27, but could be a top 1-2 for just this year 2020 and just the Deep South.

[StormySquares]

1 hour ago, nrgjeff said:

Yes models are definitely struggling. Lots of WF rain would anchor the WF. However it's a robust neutral/negatively tilted system which can push WFs around. Models keep it cool. Yet their QPF swaths hint beasts moving from southwest to northeast. Note they did that a couple times last year, and it turned out non-severe rain with thunder; so, it's not set.

One thing upstairs the turning with height is at or greater than 45 deg. That can sometimes push precipitation off boundary triggers. If it were to close up to say, 30 deg, might have a better shot at a rain-out less severe.

I will say that this is no 4/27. That day turning was nearly 90 degrees; and, a true dry line punched through Dixie. It was like a Plains outbreak. Not happening Easter. 

My bearish lean is for our Region only! Deep South could have a nasty day closer to the Gulf Coast. Still no 4/27, but could be a top 1-2 for just this year 2020 and just the Deep South.

Recent runs of the GFS, ECMWF, and UKMet have been warmer. How much do you think this would change things?

[Santa Clause]

2 hours ago, nrgjeff said:

Yes models are definitely struggling. Lots of WF rain would anchor the WF. However it's a robust neutral/negatively tilted system which can push WFs around. Models keep it cool. Yet their QPF swaths hint beasts moving from southwest to northeast. Note they did that a couple times last year, and it turned out non-severe rain with thunder; so, it's not set.

One thing upstairs the turning with height is at or greater than 45 deg. That can sometimes push precipitation off boundary triggers. If it were to close up to say, 30 deg, might have a better shot at a rain-out less severe.

I will say that this is no 4/27. That day turning was nearly 90 degrees; and, a true dry line punched through Dixie. It was like a Plains outbreak. Not happening Easter. 

My bearish lean is for our Region only! Deep South could have a nasty day closer to the Gulf Coast. Still no 4/27, but could be a top 1-2 for just this year 2020 and just the Deep South.

Imo there may never be another 4/27 in most of our lifetimes, or 1974 type so yeah understand no comparison to that.

[crossbowftw3]

My own digging through model evidence makes me think something closer to 4/24/10 or Veteran's Day 2002.

 

which wouldn't be 4/27 bad but still plenty bad on its own.

[nrgjeff]

1 hour ago, StormySquares said:

Recent runs of the GFS, ECMWF, and UKMet have been warmer. How much do you think this would change things?

They may be right, or rainy pattern recognition could score a huge coup. Praying for the latter.

[StormySquares]

Something else to watch is warming at 850 and 700 mb between 18z and 0z. This could put a cap in place over much of the warm sector by 0z. 

[Windspeed]

I agree with the whole trying to forecast a similar setup or expect another 4/27. Too many variables need to be dead nuts for that to occur. I seem to recall that 4/27 could have been even worse over the central Valley had the bulk of early onset precip along the warm front not lingered west of Knoxville. But by the time the outbreak had started, instability went nuts over the eastern Valley with warm southerly flow and it didn't matter there. Hence all the long-track tornadoes into the Chattanooga area to SWVA. That was an insane setup all for bad luck for the folks involved. Having said this, we may still be in for a bad outbreak Sunday.

[McMinnWx]

Anybody got the latest STP? I’m a newb and don’t know where to find it. Or if it’s even a relevant piece of data. Forgive my ignorance. 

[McMinnWx]

Nevermind. Found it. Good grief! Hours 81 and 84. 

[jaxjagman]

Watch the trends here the last few runs with the Upper level Ridge in the east

[jaxjagman]

The Euro 18z is even stronger with the ULR and the system goes -ve tilt into the S/plains and heads towards the Lakes

[PowellVolz]

The Euro 18z is even stronger with the ULR and the system goes -ve tilt into the S/plains and heads towards the Lakes

That puts most of Tennessee in the game right?


.

[jaxjagman]

43 minutes ago, PowellVolz said:

That puts most of Tennessee in the game right?


.

Yes sir

[jaxjagman]

.The Euro and NAM has better instability unlike the GFS.The GFS could be just as right with clouds and rain before .One thing if the GFS is right Nashville will have some problems with flash flooding

GFS 0.5 Degree FORECAST FOR: BNA    LAT=  36.12 LON=  -86.68 ELE=   591

                                            00Z APR10   * - APPROXIMATED
                6 HR    6 HR    SNCVR   TOTAL    SFC     2 M    1000    1000 
                 QPF     CVP     LIQ     QPF     PCP     TMP     500     850 
                (IN)    (IN)    (IN)    (IN)    TYPES    (C)     THK     THK 
SUN 00Z 12-APR  0.00    0.00    0.00    0.00            13.6     557     136    
SUN 06Z 12-APR  0.00    0.00    0.00    0.00      RA    12.7     558     136    
SUN 12Z 12-APR  0.06    0.00    0.00    0.06            11.2     558     135    
SUN 18Z 12-APR  0.14    0.00    0.00    0.21      RA    15.5     562     137    
MON 00Z 13-APR  2.56    0.02    0.00    2.77      RA    14.9     567     138    
MON 06Z 13-APR  0.98    0.16    0.00    3.75            16.8     558     138    
MON 12Z 13-APR  0.00    0.00    0.00    3.76      RA    11.3     554     134    
MON 18Z 13-APR  0.00    0.00    0.00    3.76             8.7     546     131    
TUE 00Z 14-APR  0.00    0.00    0.00    3.76             7.6     541     131    

 

Edit:I'm just taking about in our parts,to avoid confusion

[jaxjagman]

Getting dizzy yet ?

[Windspeed]

Getting dizzy yet ?  

 

Hoping this is just nonsense and the models suck right now. Don't feel like hype-bust but this does look bad from a modeling perspective.  Edit: Bad in that I don't like the way this is trending... don't want it, don't need it. Bust bust bust. Modeling for this event looks nasty right now but there is still plenty of time for this to not be a big bad monster outbreak.

 

 

 

 

 

[Windspeed]

If nothing else, the lower Tennessee Valley is swaying more assuredly to a tornadic outbreak. The northern Valley is still in question at this point. The parameters are there however if the airmass trench keeps shifting north. Big *if* of course.

[Windspeed]

Sharing this post concerning the SREF's sigtor probs from the SE forum:

 

I don't post here often, mostly lurk, but wanted to post the 21z SREF Sigtor probs for 21z on Sunday. 

[Windspeed]

[Windspeed]

..and not often you see a hatched area that large for a Day 3 Moderate. Potential is key. Seriousness of the situation needs to get out early. If it becomes high risk, at least we had ample warning. If it doesn't pan out, better to have heeded the eyebrow-raising model guidance than to be too conservative and to regret those that were complacent I suppose.

[jaxjagman]

4 hours ago, Windspeed said:

 

 

..and not often you see a hatched area that large for a Day 3 Moderate. Potential is key. Seriousness of the situation needs to get out early. If it becomes high risk, at least we had ample warning. If it doesn't pan out, better to have heeded the eyebrow-raising model guidance than to be too conservative and to regret those that were complacent I suppose.

 

Yeah but with the virus on-going and the stay at home policy ,people living in mobile homes will be  more vulnerable unless you lift the ban so they can seek shelter.Not a good situation to be in right now

[StormySquares]

1 hour ago, jaxjagman said:

Yeah but with the virus on-going and the stay at home policy ,people living in mobile homes will be  more vulnerable unless you lift the ban so they can seek shelter.Not a good situation to be in right now

I can't imagine the travel ban extends to people who live in mobile homes if a tornado is coming at them. Or why you would yield to the ban in the first place in such an event.

[nrgjeff]

One would think a storm shelter is essential. If any government official thinks otherwise, they should be fired and not allowed to serve ever again.

Here's the deal. If 100% of the mobile home residents get coivd-19 a few would become seriously ill and maybe 1-2 would pass away. Well, 100% won't get infected even in a crowded shelter. How about the tornado without shelter? Much much worse!

That said the 4/27 propaganda is uncalled for. I knew it'd come, but now I'm surprised coming from some otherwise reliable forecasters. Did we not hear that last year? I remember the High Risk system had like 30 degrees turning from 850/500 mb (nowhere close to the 60 deg. 4/27). Guess what? Last year busted!

OK we have a solid 45 degrees of turning progged on Sunday. It's gonna be bad. Probably ends up High Risk.  However it's not 4/27 or 1974, period. Pray for the Deep South; but, don't freak out.

[Santa Clause]

Imo won’t even be close to 4/27...that being said widespread severe weather is likely. 

[Windspeed]

Very good thread/discussion by Cameron Nixon, a post-grad atmospheric scientist doing his PHD work @ CMU. He seems to know his stuff. At any rate, knowledgeable enough to warrant sharing his thoughts on the upcoming event:

 

 

This comment in particular:

Given (likely) cloudiness and perhaps strong 850mb convergence, it is possible that elevated convection is most likely at least initially, before forcing encourages more of a linear/mixed-mode evolution. If supercells do "break the cap" initially, tornado threat will be realized.

 

 

Edit: He also does point out a worst-case scenario based on nuances in the recent ECMWF runs that suggest a small extension of the shortwave during initial phase. This would amplify the low-level flow, increase instability and allow capping to break down ahead of the linear mode.

[MUWX]

7 minutes ago, Windspeed said:

Very good thread/discussion by Cameron Nixon, a post-grad atmospheric scientist doing his PHD work @ CMU. He seems to know his stuff. At any rate, knowledgeable enough to warrant sharing his thoughts on the upcoming event:

 

 

 

This comment in particular:

 

 

 

Unless I  missing something, he doesn’t seem to think this will be a high end out break. 

[Windspeed]

Unless I  missing something, he doesn’t seem to think this will be a high end out break. 

He does give a worst case scenario that would lead to a high end outbreak however. He explains different possibilities and why, which is why I shared.