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Severe WX December 29 & 30, 2021 Severe Threat
- Thread starter KevinH
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Updated Day 2.
Pretty long discussion in the outlook, but here is the last portion :
An upgrade to enhanced (10%/sig) was considered across northern Mississippi and northwest Alabama, but ultimately settled on an expansion of the slight risk for this outlook. If guidance continues to trend toward a stronger surface low, and if CAM guidance starts to show more intense storm development, an upgrade to enhanced may be necessary.
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Pretty long discussion in the outlook, but here is the last portion :
An upgrade to enhanced (10%/sig) was considered across northern Mississippi and northwest Alabama, but ultimately settled on an expansion of the slight risk for this outlook. If guidance continues to trend toward a stronger surface low, and if CAM guidance starts to show more intense storm development, an upgrade to enhanced may be necessary.
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Don't pay attention to the exact timing with the SREF. It is historically known to have slow timing. It is what it shows as an environment that is most important.
Here is the latest run of the Baron 3k model with updraft helicity tracks overlaid. You can see multiple discrete, long-tracked supercells working through that environment. The thing about a subtle forcing/low amplitude regime like this is that it will favor a discrete storm mode. I'm not too concerned about a current lack of deeper UH tracks on the other CAMs. They are showing their cool season cold bias in the boundary layer, as evidenced by the afternoon temperatures and dewpoints they are modeling in the area of concern. When you combine that with the subtle forcing regime, it's easy to see why they lack a stronger UH signal. The fact that they have the biases they do but are still showing UH tracks at all in this regime is concerning.
My concern for Wednesday afternoon and Wednesday evening is significantly growing. I think the target zone for the highest risk is north MS, north/northwest AL, southern TN because of being closer to the mid-level forcing, being on the north/west side of the low-level jet where there is more low-level convergence and stronger low-level ascent, and closer to any mesoscale boundaries. However, the threat for severe/tornadic storms will extend significantly farther south, and the SPC outlook looks correct in that regard. Based on what I'm seeing right now, I would hope the midday Day 2 outlook today has a sigtor-driven ENH risk over north MS/AL and southern TN. I feel like this is heading toward a localized threat of a long-tracked, strong tornado or two or three in that area. Storm coverage would keep it below MDT+ criteria, but I wouldn't be shocked at all if there's an intense tornado or two, given what we see.
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There is a risk for tornadoes today across LA, MS, and possibly stretching into western Alabama.
JPWX
Member
Not much change in the new updated Day 2 Outlook from SPC. Say uncertainty in the forcing within the warm sector. Still though I can see where an Enhanced Risk upgrade is warranted.
Kory
Member
Not just forcing questions but there has been a downtrend in low level shear related to the LLJ.
akt1985
Member
A band of heavy rain has set up between Huntsville and Columbus, Mississippi tonight. I wonder if we will see any flash flood warnings towards sunrise?
Kory
Member
Looks like we get an organized complex that moves across North Central MS and North Central AL.
The enhanced region was expanded eastward a bit. It does look there will be sun today for Enh and further south. I would be ready for some sort of surprise with this one.
Kory
Member
The ongoing complex of storm across MS and what appears to be a boundary sinking south across N AL will play a huge role in placement of potential severe later today. Could very well cut out a large portion of the currently outlooked area…may need adjustments SE.
cheestaysfly
Member
Can you explain the end of your post to a weather noob like me? By "cut out a large portion" do you mean the weather conditions could get better or worse there? I'm in the enhanced area so naturally I'm hoping it won't get so bad later.
Kory
Member
If the meso low pressure does indeed follow the path on the HRRR (which is seemingly handling the current convection well) I believe a good portion N MS/Southern TN will stay in the rain cooled atmosphere…perhaps even the Shoals. A lot hinges on how this complex of rain reinforces the stable airmass behind a boundary in NE MS and N AL. This feels like a Franklin/Lamar County ENE to near Huntsville and south sort of deal.
cheestaysfly
Member
Thank you! I'm in the Shoals so I'm hoping for the best outcome today.
Bamamuscle
Member
I asked NWS about the rain this morning. Here’s the response I got.
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Bamamuscle
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CheeselandSkies
Member
Brett Adair seems to know his stuff...he doesn't get ultra overhyped like RT as far as I know. An eyebrow-raiser for sure.
CheeselandSkies
Member
SPC already considering a watch for the ARKLATEX region.
Storm Prediction Center Mesoscale Discussion 2070
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Kory
Member
15z HRRR continues to inch this further south each run. Has it going deep into AL well into the evening.
Bamamuscle
Member
Ummm wow? Is this overcooking the potential or has this trended into dangerous situation territory?
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