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Severe WX Severe threat 3/30-3/31

LoopingHodos said:
The SPC wording seems more nonchalant than I expected. May just be the lack of certainty but the threat level does not seem to be as significant even as yesterdays Day 5 outlook.
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The threat is still significant. SPC doesn’t just hand out huge Day 5 outlooks. The model consistency is all over the place. You need to look at general pattern recognition rather than model by model at this point in time. What we really know is there will be plenty of instability pushing rather far north and sufficient wind shear that could lead to big issues. What we don’t know is the trajectory of the low/placement and other mitigating factors that really won’t come into focus until we have the CAM models. Even then if there is an appreciable tornado threat we won’t really know until the morning of the event.
 
Bulkshear said:
The threat is still significant. SPC doesn’t just hand out huge Day 5 outlooks. The model consistency is all over the place. You need to look at general pattern recognition rather than model by model at this point in time. What we really know is there will be plenty of instability pushing rather far north and sufficient wind shear that could lead to big issues. What we don’t know is the trajectory of the low/placement and other mitigating factors that really won’t come into focus until we have the CAM models. Even then if there is an appreciable tornado threat we won’t really know until the morning of the event.
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We're also kindve in the funky transition period from Globals to Cams. GFS doesn't look all that impressive, but a shift back in the other direction could happen anytime. The event on the 15th, went through this funky phase from what I remember where it didn't look as impressive as what it was and then came back to being super impressive within like 24-36 hours. Just my 2 cents. It'll be fun to watch model trends
 
UncleJuJu98 said:
We're also kindve in the funky transition period from Globals to Cams. GFS doesn't look all that impressive, but a shift back in the other direction could happen anytime. The event on the 15th, went through this funky phase from what I remember where it didn't look as impressive as what it was and then came back to being super impressive within like 24-36 hours. Just my 2 cents. It'll be fun to watch model trends
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Regardless of what does happen, the confidence is there for a pretty widespread severe weather event.
 
Adding on to it, I'm not that surprised SPC remained a 15%. FWIW, I believe it should be mentioned that the GFS in the past 24 hours has really dropped off the amount of CAPE, as well as SRH values cross the risk area (see 06z GFS from yesterday vs today), specifically across the eastern part of Arkansas to the eastern part of Tennessee including northern Alabama (specifically across the Huntsville NWS CWA). If it remains consistent, this would remain a damaging wind threat rather than tornadic.

Will be interesting to see where the GFS 12z and 18z trend later today, and see if it ramps back up. Eager as well to see the NAM runs come in.
 
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NWS Birmingham morning AFD:
"Upper-air pattern and height falls along with
deep layer shear will be favorable for supercells to move across
the area after midnight Sunday night, probably eventually becoming
more linear by Monday morning.

The positive tilt orientation of the front could actually aid in
supercells having more "room to roam" in the pre-frontal warm
sector. Parameters will be favorable for large hail, damaging
winds, and at least isolated tornadoes. The magnitude of the
tornado threat is where the uncertainty lies. Looking at cluster
analyses, there is very little overlap between the EPS and GEFS
members while the GEPS members lie somewhere in between. The EPS
members indicate stronger 500mb and 850mb winds than the GEFS
members, as well as more backed surface winds. Also, the
deterministic ECMWF indicated a more upright (north-south)
convection orientation, with convection appearing to initiate on a
pre-frontal trough. These mesoscale details will need to be
monitored closely, as they will determine whether there is more of
an isolated tornado threat vs. a more concerning overnight strong
tornado threat."

I am concerned about the supercell potential across MS as well.
 
I ran my WRF-ARW model yesterday, but life got in the way, and I wasn't able to run analysis on it and post the results. Here it is for anyone interested. This initialized at 12z *yesterday* and is at 9 km resolution.

First up is the Composite Radar. I snapped an image of it in the evening hours on Sunday. The general idea is pockets of cells initiate overnight in MS and TN and propagate eastward.

1743082405592.png


A stout 2k-3k SBCAPE permeates the area, which gives the storms fuel to thrive.

1743082497400.png


As somewhat of a new metric, this is the Vertically Integrated Graupel. Graupel in convective storms is highly associated with storm cores, lightning, and hail. We see here it highlights a line of discrete storm cores going through MS into TN.

1743082587842.png


Below is a new metric I'm calling the Storm Mode Index, which is essentially an extension of the Bulk Richardson Number to account for helicity and a few other metrics. I've also overlaid the hodographs on top of this plot. You see in the open warm sector, it largely favors discrete (potentially tornado-producing) supercells with curved hodographs, and a multicellular/linear threat along the front itself.

1743082869180.png


I plan to do another run today and see what the new data say. From looking at the GFS, Euro, and ensembles (in addition to this), I feel it's possible the threats may not be widespread but rather scattered, but where they do form, they could be problematic.
 
wx_guy said:
I ran my WRF-ARW model yesterday, but life got in the way, and I wasn't able to run analysis on it and post the results. Here it is for anyone interested. This initialized at 12z *yesterday* and is at 9 km resolution.

First up is the Composite Radar. I snapped an image of it in the evening hours on Sunday. The general idea is pockets of cells initiate overnight in MS and TN and propagate eastward.

View attachment 37341


A stout 2k-3k SBCAPE permeates the area, which gives the storms fuel to thrive.

View attachment 37343


As somewhat of a new metric, this is the Vertically Integrated Graupel. Graupel in convective storms is highly associated with storm cores, lightning, and hail. We see here it highlights a line of discrete storm cores going through MS into TN.

View attachment 37345


Below is a new metric I'm calling the Storm Mode Index, which is essentially an extension of the Bulk Richardson Number to account for helicity and a few other metrics. I've also overlaid the hodographs on top of this plot. You see in the open warm sector, it largely favors discrete (potentially tornado-producing) supercells with curved hodographs, and a multicellular/linear threat along the front itself.

View attachment 37346


I plan to do another run today and see what the new data say. From looking at the GFS, Euro, and ensembles (in addition to this), I feel it's possible the threats may not be widespread but rather scattered, but where they do form, they could be problematic.
Click to expand...
Fascinating writeup! Always enjoy reading your analysis from using your weather model.

I agree that judging so far by the models, it's going to be more of a scattered event (unknown obviously where they'll form), but where they do form, they could be problematic.

Altogether, there's just a lot of uncertainty and disagreements between the GFS and other models (especially ECMWF). I think whenever we get the NAM & NAMNST data in for the event this weekend, we'll finally start to get the answers needed (or at least more confidence).
 
I get most interested in a storm system after it comes ashore. I still look at model guidance prior to, but more so after. I see this morning that the SPC has introduced a categorical risk for Saturday and for Sunday kept the 15% risk which makes sense for the time being. It's not completely out of the question that the Sunday event could turn out to be messy after dark squall line with a few spin up tornadoes.
 
From a Sunday night Supercell potential standpoint, that's similar to the previous event (14th/15th) in that regard. That's the only similarity I see. From what I've seen and reading between the lines, the bulk of the activity, at least for North MS down into Central MS, would not be starting until prior to/just after Sunset Sunday. If that turns out correct, it would be very problematic. I also don't buy into this being JUST a QLCS (aka Squall Line) event.
 
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