• Hello, please take a minute to check out our awesome content, contributed by the wonderful members of our community. We hope you'll add your own thoughts and opinions by making a free account!

Severe 3/17/21 Severe Weather Outbreak Al/Ms/Tn/Ar nowcast

I wonder when a Tornado Watch will be issued for GA ? With a PDS watch literally on the border of GA i'm guessing a tornado watch is pretty much a guarantee.
 
07F2FF15-F2C5-4522-BCAC-BD1E9E9DF808.jpeg

DISCUSSION...Widespread strong to severe storms are ongoing across
much of northern Alabama. Storms have transitioned to a
predominately linear mode over the last two hours, suggesting a
shift toward a damaging wind threat. However, strong low-level shear
(0-1km SRH 400 m2s2) as sampled from the HTX radar and university
soundings remains in place across northern Alabama and southern
Tennessee. As storms move east into more marginal buoyancy, (250-500
J/kg MUCAPE) along and northeast of the diffuse frontal zone
tonight, there remains a chance for a tornado along with the threat
of damaging wind gusts. The threat will likely begin to decrease
after 03 to 04Z as storms move into an increasingly unfavorable
environment for severe weather.
 
Also — do these QLCS/squall lines EVER move through as slowly as modeled? It seems like no matter the forecast, once the line is in Mississippi you can count on the event being over within 3-4 hours (for Birmingham) every single time
 
I try hard not to ask questions and just read and learn, and yes I'm on the fringes of the severe, but is the jet really going to kick in that much/ front actually get here that I need to worry? It just looks like a mess, not even like a 'regular' QLCS headed this way.
 
The line is entering my county now, if it's going to go back severe, I would expect it would here since we haven't had any rain all day. Either way, it needs to push through so I can get some sleep.
 
My thoughts:

1: Round one failed because of meager low level helicity. I’ve seen it many times and this is what happens when 0-1km helicity is 150-200. You have storms spin like a top, with little ground truth unless the storm rides a boundary or it strengthens enough to finally get a tornado down for a short period of time. This was pretty well modeled.

2. I believe round two failed because of unidirectional flow aloft. This lead to messy storm modes which also helped work over the area. Most of the modeled helicity was speed shear not directional shear(the opposite happened over AL)This was also well modeled.

3. Initiation of supercells the occurred earlier and speed of the squall line also helped. The past few days had supercell initiation over central AL at or around 21z to 0z, however supercells were being initiated by 11am this morning. Slow them down and the shear increases some, although I don’t know if it changes the event.

4. The CAMs were throwing out warning after warning with the overall lack of UH streaks over the high risk area. These are never fully accurate and bust often, but when models that absolutely love to nuke the area don’t nuke the area, they may be on to something.
 
A few areas in that line sorta have that shape a little bit like they could rotate. I am honestly surprised there not at least severe thunderstorm warnings for this line.



b139ecafc85180d5c921343c1b657df3.jpg



Sent from my iPhone using Tapatalk
 
Arcc said:
My thoughts:

1: Round one failed because of meager low level helicity. I’ve seen it many times and this is what happens when 0-1km helicity is 150-200. You have storms spin like a top, with little ground truth unless the storm rides a boundary or it strengthens enough to finally get a tornado down for a short period of time. This was pretty well modeled.

2. I believe round two failed because of unidirectional flow aloft. This lead to messy storm modes which also helped work over the area. This was also well modeled.

3. Initiation of supercells the occurred earlier and speed of the squall line also helped. The past few days had supercell initiation over central AL at or around 21z to 0z, however supercells were being initiated by 11am this morning.

4. The CAMs were throwing out warning after warning with the overall lack of UH streaks over the high risk area. These are never fully accurate and bust often, but when models that absolutely love to nuke the area don’t nuke the area, they may be on to something.
Click to expand...
Ya I wound drop the high and MDT to be honest. I would only go MDT for SE GA and the Carolinas tomorrow.
 
I mean there were still over 20 tornadoes reported today. Doesn't sound like most of them did much damage, though. Not sure if that meets the criteria for a high risk and PDS watch, though. I don't think tomorrow will meet the hype the local mets here are giving it.
 
Arcc said:
My thoughts:

1: Round one failed because of meager low level helicity. I’ve seen it many times and this is what happens when 0-1km helicity is 150-200. You have storms spin like a top, with little ground truth unless the storm rides a boundary or it strengthens enough to finally get a tornado down for a short period of time. This was pretty well modeled.

2. I believe round two failed because of unidirectional flow aloft. This lead to messy storm modes which also helped work over the area. Most of the modeled helicity was speed shear not directional shear(the opposite happened over AL)This was also well modeled.

3. Initiation of supercells the occurred earlier and speed of the squall line also helped. The past few days had supercell initiation over central AL at or around 21z to 0z, however supercells were being initiated by 11am this morning. Slow them down and the shear increases some, although I don’t know if it changes the event.

4. The CAMs were throwing out warning after warning with the overall lack of UH streaks over the high risk area. These are never fully accurate and bust often, but when models that absolutely love to nuke the area don’t nuke the area, they may be on to something.
Click to expand...

What do you expect as the storms get into E/SE Alabama?
 
Arcc said:
My thoughts:

1: Round one failed because of meager low level helicity. I’ve seen it many times and this is what happens when 0-1km helicity is 150-200. You have storms spin like a top, with little ground truth unless the storm rides a boundary or it strengthens enough to finally get a tornado down for a short period of time. This was pretty well modeled.

2. I believe round two failed because of unidirectional flow aloft. This lead to messy storm modes which also helped work over the area. Most of the modeled helicity was speed shear not directional shear(the opposite happened over AL)This was also well modeled.

3. Initiation of supercells the occurred earlier and speed of the squall line also helped. The past few days had supercell initiation over central AL at or around 21z to 0z, however supercells were being initiated by 11am this morning. Slow them down and the shear increases some, although I don’t know if it changes the event.

4. The CAMs were throwing out warning after warning with the overall lack of UH streaks over the high risk area. These are never fully accurate and bust often, but when models that absolutely love to nuke the area don’t nuke the area, they may be on to something.
Click to expand...

Been lurking most of this event. I always was wary of this event from the storm modes on models. That’s always my number one factor when dealing with tornado outbreaks.

If models have multicellular clusters and super messy storm mode it honestly doesn’t matter how PDS TOR your soundings are. Soundings are just POTENTIAL energy that can be used by a storm. They are not guaranteeing a EF5 tornado. With this type of storm mode you are cutting the efficiency of storms to use that energy in half atleast. And you have a ton of cells all sucking in that energy opposed to 5-10 individual cells.

if we had discreet cells today. Sure, you’d have multiple ef3+ long tracked tornadoes. But that just simply was never going to be the case. The NAM and HRRR never showed discreet cells as the primary storm mode. It was always this messy junk.

Thankfully, today was a recipe for storms to not “live up to the hype.” I know it’s easy to say in hindsight but that really was my thinking most of the time. To me storm mode is everything for tornadoes. I’ve seen a discreet cell drop a tornado in extremely marginal conditions. It is all about how efficiently a storm is able to use that energy available.
 
Fountainguy97 said:
Been lurking most of this event. I always was wary of this event from the storm modes on models. That’s always my number one factor when dealing with tornado outbreaks.

If models have multicellular clusters and super messy storm mode it honestly doesn’t matter how PDS TOR your soundings are. Soundings are just POTENTIAL energy that can be used by a storm. They are not guaranteeing a EF5 tornado. With this type of storm mode you are cutting the efficiency of storms to use that energy in half atleast. And you have a ton of cells all sucking in that energy opposed to 5-10 individual cells.

if we had discreet cells today. Sure, you’d have multiple ef3+ long tracked tornadoes. But that just simply was never going to be the case. The NAM and HRRR never showed discreet cells as the primary storm mode. It was always this messy junk.

Thankfully, today was a recipe for storms to not “live up to the hype.” I know it’s easy to say in hindsight but that really was my thinking most of the time. To me storm mode is everything for tornadoes. I’ve seen a discreet cell drop a tornado in extremely marginal conditions. It is all about how efficiently a storm is able to use that energy available.
Click to expand...

Well had we had 0-1km helicity across AL around 300 today, it verifies the High easy. However that can be said for a handful of events over the past years as well. Also it’s not like the helicity here busted low, it was fairly well modeled.
 
Last edited:
I still can’t get over the Easter Sunday setup, shear was there but it was so messy, imo that setup had a shot to be close to 2011 vs this one
 
Some impressive rainfall totals in some areas, other areas haven't gotten anything.

Capture.JPG
 
I wouldn’t at all be surprised to see a few brief spin ups in that line. And they may not even get a Tornado warning for all of them. You can see hints of a little rotation


269bc51dd5f8e483f0ff4b35b2b5bf27.jpg



Sent from my iPhone using Tapatalk
 
You must log in or register to reply here.
Back
Top