April 12 Severe Event

[Amped]

1 minute ago, Quincy said:

If you want supercell tornadoes, steeper low-level lapse rates are preferred. If you have a QLCS moving into an area with marginal lapse rates, like we’ve had today (around 5-5.5 C/km), but substantial low-level shear, that’s different. 

If you dig back, I cited that 6-6.5 C/km lapse rates will get it done. If you look at mesoanalysis right now, that’s confined to southern MS/LA. They’re barely around 5 C/km along the warm front, which is where SPC has been highlighting an “enhanced” sig tor potential.

As the warm front lifts, you should see lapse rates improve a bit, mainly down near I-20, not up near the TN border. 

The warm front is creating heavy WAA precip and slowing itself down. This is part of the problem.  

Things may change if it eventually makes a northward surge in a few hours.

[Radtechwxman]

7 minutes ago, Quincy said:

If you want supercell tornadoes, steeper low-level lapse rates are preferred. If you have a QLCS moving into an area with marginal lapse rates, like we’ve had today (around 5-5.5 C/km), but substantial low-level shear, that’s different. 

If you dig back, I cited that 6-6.5 C/km lapse rates will get it done. If you look at mesoanalysis right now, that’s confined to southern MS/LA. They’re barely around 5 C/km along the warm front, which is where SPC has been highlighting an “enhanced” sig tor potential.

As the warm front lifts, you should see lapse rates improve a bit, mainly down near I-20, not up near the TN border. 

Couldn't agree more. Seems like better low level instability isn't lining up well with best shear. Then the storm mode is very messy, esp near the warm front

[Quincy]

Just now, Amped said:

The warm front is creating heavy WAA precip and slowing itself down. This is part of the problem.  

Things may change if it eventually makes a northward surge in a few hours.

Today is a good example of why STP is not always helpful. Sure, it’s maxed out near the warm front, but lapse rates are sub-marginal.

We had a high risk bust in Oklahoma last year that was largely due to junky lapse rates. 6 C/km is a good benchmark. 6.5 C/km is the mean for most tornado environments.

I’m curious to see what happens down in LA/southern MS. Can the convection remain sustained? If so, does it evolve into a broken line? There’s good 0-3km CAPE, steeper lapse rates and strong low-level flow there. 

[SluggerWx]

Cell tops in SW MS are now > 40,000 feet. 

[DanLarsen34]

1 minute ago, Quincy said:

Today is a good example of why STP is not always helpful. Sure, it’s maxed out near the warm front, but lapse rates are sub-marginal.

We had a high risk bust in Oklahoma last year that was largely due to junky lapse rates. 6 C/km is a good benchmark. 6.5 C/km is the mean for most tornado environments.

I’m curious to see what happens down in LA/southern MS. Can the convection remain sustained? If so, does it evolve into a broken line? There’s good 0-3km CAPE, steeper lapse rates and strong low-level flow there. 

Today reminds me of that day a lot, at least at the moment. 

[jrips27]

Area Forecast Discussion
National Weather Service Peachtree City GA
332 PM EDT Sun Apr 12 2020


...INCREASED CONCERN OF SIGNIFICANT SEVERE WEATHER OUTBREAK LATE 
TODAY INTO EARLY MONDAY MORNING...

.SHORT TERM /Rest of today through Monday Night/...

Things should ramp up quickly here for a significant outbreak of 
severe storms (possibly the strongest event in at least the last 2 
to 3 years) having the big three main threats of strong long- 
track tornadoes, damaging winds, and large hail this afternoon 
into the overnight. Much of the western CWA remains in a Moderate 
Risk with the rest of the area in an Enhanced, though the storm
threats could occur area-wide. All the recent convective 
development across the western and northern CWA has been tapping 
into mostly elevated instability, though concern is increasing 
with the evolution of a warm front/lingering wedge front across
portions of north Georgia (currently extending near the Atlanta 
Metro to just south of Athens) as this may end up focusing some 
stronger rotating convection tapping into more surface based 
energy along with localized enhanced low level helicity and 
frontogenetic forcing on top of the ample upper forcing/jet 
dynamics. The HRRR continues to ramp up the Sig Tor Param along 
and south of this feature that could slowly lift northward this 
afternoon into evening and bulk shear vectors have strong veering,
so will need to watch for discrete supercell and tornado 
potential even ahead of the main overnight expected storms.

Hi-res CAM consensus continues to have expected intense convective 
zones/broken lines with embedded supercells pushing into the CWA 
after about 04z (midnight) tonight pushing eastward through the 
early morning hours. The HRRR indicates impressive swaths of updraft 
helicity along these storms interacting with over 400 m2/s2 of 0-1km 
SRH, so there is concern of some strong long-track tornadoes, even 
more dangerous given the nocturnal timing. Regardless there will be 
a widespread damaging wind threat with a robust 65 kt LLJ and 80-100 
kts of bulk deep layer shear as the upper wave swings negative. 

[DanLarsen34]

 

[cheese007]

2 minutes ago, Quincy said:

We had a high risk bust in Oklahoma last year that was largely due to junky lapse rates. 6 C/km is a good benchmark. 6.5 C/km is the mean for most tornado environments.

 

So many folks threw in the towel after that day that the incredibly active following weeks of severe weather basically got no attention. SPC learned their lesson this year sticking with the MOD 

[Radtechwxman]

Just now, DanLarsen34 said:

https://twitter.com/wxmann/status/1249411874510106624?s=20

Was just about to post this. Very interesting. Wonder if that lead wave left some subsidence behind it

[Quincy]

By the way, it’s been mentioned, but the convective line that produced QLCS tornadoes has been accelerating somewhat ahead of schedule. The HRRR depiction hasn’t been far off, but it’s been enough to lead to a messy evolution north of I-20.

Aside from the southern target this afternoon, maybe this is mostly a late afternoon/evening event. Once the LLJ really cranks tonight, I think bad news is spelt for AL.

[SnowGoose69]

2 minutes ago, cheese007 said:

So many folks threw in the towel after that day that the incredibly active following weeks of severe weather basically got no attention. SPC learned their lesson this year sticking with the MOD 

That was more or less a clear air bust wasn’t it?  My memory is there was a massive burst of AM convection that killed instability but even though it totally cleared out for hours after nothing ever happened 

[BhamParker]

I am fairly concerned here just to the SW of Birmingham about later. HRRR has been consistent on some very strong storms in the line that I believe will have some embedded tornadoes. My home is in an area that has produced some dangerous tornadoes in the past.

[SouthernNJ]

In the heavy rainfall, a narrow line has formed near Oxford MS and appears to

be getting stronger winds within.

[cheese007]

2 minutes ago, SnowGoose69 said:

That was more or less a clear air bust wasn’t it?  My memory is there was a massive burst of AM convection that killed instability but even though it totally cleared out for hours after nothing ever happened 

There were a fair few tornadoes but nothing near what was expected of an >95% all hazards PDS watch. Proof that 1 in 20 chances do, in fact, happen 

[DanLarsen34]

3 minutes ago, SnowGoose69 said:

That was more or less a clear air bust wasn’t it?  My memory is there was a massive burst of AM convection that killed instability but even though it totally cleared out for hours after nothing ever happened 

Not really. We had a bunch of storms try to fire across the warm sector, but none of them were ever able to take off. They were a lot like the WAA storms we’re seeing right now. Any time it looked like one had a shot, it crashed over the surging front and died too. 

[MUWX]

4 minutes ago, cheese007 said:

There were a fair few tornadoes but nothing near what was expected of an >95% all hazards PDS watch. Proof that 1 in 20 chances do, in fact, happen 

It isn’t a 95% all hazard watch though

[cheese007]

Just now, MUWX said:

It isn’t a 95% all hazard watch though

Exactly. So I don't know why folks are so shocked this is under-performing 

[DanLarsen34]

I’m beginning to wonder if we even end up with 5-10 tornadoes in the PDS watch across Mississippi at this point. Line has advanced pretty far across the watch area. The embedded cell might have been the only shot we have to get there. (Key word is might). 

[SmokeEater]

By the way, it’s been mentioned, but the convective line that produced QLCS tornadoes has been accelerating somewhat ahead of schedule. The HRRR depiction hasn’t been far off, but it’s been enough to lead to a messy evolution north of I-20.
Aside from the southern target this afternoon, maybe this is mostly a late afternoon/evening event. Once the LLJ really cranks tonight, I think bad news is spelt for AL.

James Spann's been pushing this for AL, he's been saying after 5-6pm for AL for a couple days now.

Sent from my SM-G973U using Tapatalk

[janetjanet998]

BULLETIN - EAS ACTIVATION REQUESTED  
TORNADO WARNING  
NATIONAL WEATHER SERVICE JACKSON MS  
251 PM CDT SUN APR 12 2020  
  
THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A  
  
* TORNADO WARNING FOR...  
  SOUTHEASTERN CHOCTAW COUNTY IN CENTRAL MISSISSIPPI...  
  NORTHWESTERN NOXUBEE COUNTY IN EAST CENTRAL MISSISSIPPI...  
  SOUTHERN OKTIBBEHA COUNTY IN NORTHEASTERN MISSISSIPPI...  
  NORTHERN WINSTON COUNTY IN EAST CENTRAL MISSISSIPPI...  
  
* UNTIL 345 PM CDT.  
          
* AT 250 PM CDT, A CONFIRMED TORNADO WAS LOCATED NEAR ACKERMAN, OR 13  
  MILES NORTHWEST OF LOUISVILLE, MOVING EAST AT 45 MPH.  
  
  HAZARD...DAMAGING TORNADO.  
  
  SOURCE...RADAR CONFIRMED TORNADO.  

[LithiaWx]

3 minutes ago, DanLarsen34 said:

I’m beginning to wonder if we even end up with 5-10 tornadoes in the PDS watch across Mississippi at this point. Line has advanced pretty far across the watch area. The embedded cell might have been the only shot we have to get there. (Key word is might). 

Does that mean the threat increased farther east towards AL and west GA or just less tornadoes from this system in general?

[audioguy3107]

From the radar, it does appear that the line of storms in Mississippi is breaking up....whether this translates into more dangerous discrete cells remains to be seen.

[DanLarsen34]

1 minute ago, LithiaWx said:

Does that mean the threat increased farther east towards AL and west GA or just less tornadoes from this system in general?

This was just a comment on the threat in Mississippi right now. Alabama and Georgia are still facing a potentially significant threat a few hours from now. Don’t let your guard down.

[JakkelWx]

New storms have fired across Louisiana currently. They've already gotten pretty large and they seem to be outflow induced storms. Once they enter the MDT risk zone things could get ugly.

I've also noticed clearing behind the storms to the east and there is still lots of daylight left.

[ATLTHRASHER]

6 minutes ago, LithiaWx said:

Does that mean the threat increased farther east towards AL and west GA or just less tornadoes from this system in general?

The soundings near my house in NW GA are still looking nasty...

[Eskimo Joe]

Believe this now has a visually confirmed tornado with it:

 

[SouthernNJ]

Seeing a few areas, one near Louisville, a stronger one near Noxapater, both

are in the southern of the two polygons are could do something.

[yoda]

[Solak]

Central NC specific from latest RAH AFD.

The severe threat is looking increasingly alarming. IMO the most 
remarkable/concerning aspect is the HREF high probabilities(80-90%) 
that show moderate instability(1000-1500 J/Kg) spreading west to 
east across central NC, amidst the large 0-1 km hodographs and 400-
500 m/s of helicity created by the incredibly strong low-level shear 
moving through the region. This environment will be highly conducive 
for widespread thunderstorm wind damage, tornadoes and large hail 
across the area between 09Z(4am) to 16z(Noon), with the pending of 
evolution/mode of the convection(line/bow segment vs. discrete 
supercells) playing a critical role in what the main severe threat 
will be.  

[yoda]

3 minutes ago, yoda said: