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April 5-6 Severe Threat

MattPetrulli

By MattPetrulli,
in Southeastern States

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FlatLander48

FlatLander48

Posted
Posted
9 minutes ago, Wmsptwx said:

We need some of our heavy hitters in severe to weigh in. This one is tough, plenty of precip and cloud debris, going to be touch and go. Where is the usual gang btw? 

I would suspect they start filing in late this morning and very early afternoon. It's going to get real busy in a few hours and gonna last til after midnight.

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Buckeye05

Buckeye05

Posted
Posted
13 minutes ago, Wmsptwx said:

We need some of our heavy hitters in severe to weigh in. This one is tough, plenty of precip and cloud debris, going to be touch and go. Where is the usual gang btw? 

Rapid destabilization is already in progress. This is the kind of dynamic system that won't require massive clearing to establish a good EML and surface based CAPE. This event's verification will likely hinge on kinematics and mesoscale features rather than thermo, as its looking likely (and it has been for a while) we will be dealing with a powder keg by this late afternoon and evening. The question is will the winds back adequately and will SRH be sufficient. If anything, these morning storms are just laying down boundaries that could potentially enhance the threat later on.

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Wmsptwx

Wmsptwx

Posted
Posted
4 minutes ago, Buckeye05 said:

Rapid destabilization is already in progress. This is the kind of dynamic system that won't require massive clearing to establish a good EML and surface based CAPE. This event's verification will likely hinge on kinematics and mesoscale features rather than thermo, as its looking likely (and it has been for a while) we will be dealing with a powder keg by this late afternoon and evening. The question is will the winds back adequately and will SRH be sufficient. If anything, these morning storms are just laying down boundaries that could potentially enhance the threat later on.

Now we're talking, great details. Look forward to all of your takes throughout the day.

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Calderon

Calderon

Posted
Posted

Starting to get a little concerned with the activity pushing east from eastern Alabama because that's laying down a nice boundary that'll serve as a focus for potential for any storm that rides it later today. Where will it set up and how far will it mix remains to be seen. I do have connections to another NWS office and they're noticing it as well and is an area of concern.

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kayman

kayman

Posted
Posted

The LLJ is starting to take its role in setting things for a severe weather episode up very quickly.  There is reports of breaks in the clouds and sunshine in Tuscaloosa and Demopolis in Alabama, so that is confirming to me the LLJ already at work.

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kayman

kayman

Posted
Posted
3 minutes ago, audioguy3107 said:

Most of the convection east of Atlanta looks to miss the majority of the metro to the NW.  Looks like everything is really trying to push of to the north now.  Keep in mind most of the guidance yesterday had us socked in here until about 1PM......it's possible it's moving north a little quicker than expected.

Yeah, that's the "bounce" to the north-northeast I started to see about an hour ago on the GOES 16 satellite data.   The lull is about to start very soon in the areas between Birmingham and Atlanta and north of Montgomery... 

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pbrussell

pbrussell

Posted
Posted
8 minutes ago, Buckeye05 said:

Rapid destabilization is already in progress. This is the kind of dynamic system that won't require massive clearing to establish a good EML and surface based CAPE. This event's verification will likely hinge on kinematics and mesoscale features rather than thermo, as its looking likely (and it has been for a while) we will be dealing with a powder keg by this late afternoon and evening. The question is will the winds back adequately and will SRH be sufficient. If anything, these morning storms are just laying down boundaries that could potentially enhance the threat later on.

Mmm. Outflow boundaries. Another added level of complexity to the forecast. 

There's not much doubt if the instability will be there. Models have been pretty consistent there run to run. Cape values are so fat that the lower SRH values may (and likely will be) overcome. I'm so new to forecasting though that I barely know what I'm talking about. Time will tell. 

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jrips27

jrips27

Posted
Posted

mcd0440.gif

   Concerning...Outlook upgrade 

   Valid 051443Z - 051645Z

   SUMMARY...Portions of the states of AL/GA/SC are being considered
   for an Outlook upgrade -- though the details are still being
   analyzed.  A very notable dry bias is apparent in the latest model
   guidance, and observational data and previous model runs are being
   heavily referenced in Outlook preparation.

   DISCUSSION...GPS PW data are exhibiting a low bias by at least 0.5
   inch from parts of AL into GA, which has influenced initialization
   of the latest numerical weather prediction guidance.  Per
   coordination with the Weather Prediction Center, it appears that
   related initialization is causing substantial dry biases in model
   guidance -- extended through the Day 1 forecast period.  With an
   inland influx of rich moisture feeding ongoing intense supercells in
   southern AL (with dewpoints into the middle 70s), and the
   around-16.6-g/kg mean mixing ratio per LIX 12Z sounding, and around
   1.5-inch PW per Atlanta and Birmingham 12Z soundings, it is evident
   that rich moisture and related strong buoyancy does indeed extend
   inland. As such, observational data and previous model runs will
   play a major role in the consideration for a High Risk upgrade, as
   the dry bias has influenced the latest model guidance. While an
   Outlook upgrade is possible, it is not certain.
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Buckeye05

Buckeye05

Posted
Posted
15 minutes ago, pbrussell said:

Mmm. Outflow boundaries. Another added level of complexity to the forecast. 

There's not much doubt if the instability will be there. Models have been pretty consistent there run to run. Cape values are so fat that the lower SRH values may (and likely will be) overcome. I'm so new to forecasting though that I barely know what I'm talking about. Time will tell. 

This is a "wait and see" setup in my opinion. Almost everything is there for a big event, but the hodos/wind profile are rather unidirectional across this part of the threat area, and it will take other factors (already mentioned) in play to compensate for this. This doesn't exactly sit well with me. I've seen events that seem to have it all going for them but end up "underperforming" purely because of the wind profile, so I'm not quite as on board with this setup as some others are. So will these other compensating factors pull through? I have no idea. At least across the southern portion of the threat area, this could be one of those events where we have a lot of cells that aren't doing too much, but one or two end up latching onto a boundary and going nuts. Because the kinematics are looking like they will be mesoscale-driven, I don't expect every single storm to be spinning like a top for when round 2 arrives, at least initially. 

Maybe i'm just a bit pessimistic from the other two High Risks this year, but I don't know if i'm totally on board for an upgrade to High at this point.

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Wmsptwx

Wmsptwx

Posted
Posted
1 minute ago, Buckeye05 said:

This is a "wait and see" setup in my opinion. Almost everything is there for a big event, but the hodos/wind profile are rather unidirectional across this part of the threat area, and it will take other factors (already mentioned) in play to compensate for this. This doesn't exactly sit well with me. I've seen events that seem to have it all going for them but end up "underperforming" purely because of the wind profile, so I'm not quite as on board with this setup as some others are. So will these other compensating factors pull through? I have no idea. At least across the southern portion of the threat area, this could be one of those events where we have a lot of cells that aren't doing too much, but one or two end up latching onto a boundary and going nuts. Because the kinematics are looking like they will be mesoscale-driven, I don't expect every single storm to be spinning like a top for when round 2 arrives, at least initially. 

Maybe i'm just a bit pessimistic from the other two High Risks this year, but I don't know if i'm totally on board for an upgrade to High at this point.

Glad you brought that up, profile has kinda had me a little tentative on a major outbreak. Basically, like you state it will be a wait and see afternoon. 

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pbrussell

pbrussell

Posted
Posted
2 minutes ago, Buckeye05 said:

This is a "wait and see" setup in my opinion. Almost everything is there for a big event, but the hodos/wind profile are rather unidirectional across this part of the threat area, and it will take other factors (already mentioned) in play to compensate for this. This doesn't exactly sit well with me. I've seen events that seem to have it all going for them but end up "underperforming" purely because of the wind profile, so I'm not quite as on board with this setup as some others are. So will these other compensating factors pull through? I have no idea. At least across the southern portion of the threat area, this could be one of those events where we have a lot of cells that aren't doing too much, but one or two end up latching onto a boundary and going nuts. Because the kinematics are looking like they will be mesoscale-driven, I don't expect every single storm to be spinning like a top for when round 2 arrives, at least initially. 

Maybe i'm just a bit pessimistic from the other two High Risks this year, but I don't know if i'm totally on board for an upgrade to High at this point.

I don't think there's anything wrong at all with your reasoning here. I'm on the wait and see boat as well. The hodographs/forecasted wind direction just isn't quite where I think they need to be for a high risk at the moment. But then, I'm not a meteorologist either ;)

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Thrasher Fan

Thrasher Fan

Posted
Posted
4 minutes ago, Buckeye05 said:

This is a "wait and see" setup in my opinion. Almost everything is there for a big event, but the hodos/wind profile are rather unidirectional across this part of the threat area, and it will take other factors (already mentioned) in play to compensate for this. This doesn't exactly sit well with me. I've seen events that seem to have it all going for them but end up "underperforming" purely because of the wind profile, so I'm not quite as on board with this setup as some others are. So will these other compensating factors pull through? I have no idea. At least across the southern portion of the threat area, this could be one of those events where we have a lot of cells that aren't doing too much, but one or two end up latching onto a boundary and going nuts. Because the kinematics are looking like they will be mesoscale-driven, I don't expect every single storm to be spinning like a top for when round 2 arrives, at least initially. 

Maybe i'm just a bit pessimistic from the other two High Risks this year, but I don't know if i'm totally on board for an upgrade to High at this point.

While I haven't been able to study the previous High Risks this year as much as I'd like, I would agree with all of this.

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