Severe WX Severe Threat 17-18 March 2021

[Richardjacks]

wow going trough the 12z NAM, the shear is up also instability..although I got to wonder if it is too quick in developing showers in the afternoon. Although it isn't a CAM model, it is trying to show a couple of supercells. The warm sector should have wider/cleaner look that will likely lead to explosive development in east Miss/west Al/TN by mid afternoon. While northwest Alabama could have the highest risk, the I65 corridor for all of north Alabama up into Tennessee will very much be into play.

 

[Fred Gossage]

And the low-level jet only ramps up toward sunset and increases the tornado risk deep into central Alabama.

 

[Austin Dawg]

I hate days like this. My entire state (Mississippi) is under the gun. It’s spring break week so I’m worried about kids home alone. I wouldn’t be surprised if we end up at the school at some point on Wednesday (the cafeteria/gym is a tornado shelter).

Me too. I still have a lot of family and friends in MS and AL.

 

[andyhb]

A large region of destabilization/good lapse rates, strong low level/deep layer shear, moderate forcing for ascent, and very favorable track to the surface low? It’s no wonder the CIPS analogs are pulling so many significant events. Warm sectors like this in March are not to be messed with.

 

[Richardjacks]

A large region of destabilization/good lapse rates, strong low level/deep layer shear, moderate forcing for ascent, and very favorable track to the surface low? It’s no wonder the CIPS analogs are pulling so many significant events. Warm sectors like this in March are not to be messed with.

That pretty much sums it up...What really concerns me is the instability really approaching that of an April/later Spring event while the shear more in line with a March event...if the low level jet wasn't increasing over time, this would not be quite as alarming. The shear and instability are well matched.

 

[Matt Grantham]

NAM is on an island with the strength of the 500/850mb winds. The globals continue to downtrend. This is going to be critical for tornado production.

 

[tennessee storm chaser]

NAM is on an island with the strength of the 500/850mb winds. The globals continue to downtrend. This is going to be critical for tornado production.

Low level sheer appears be upwards though . If that continues anything get going it’s going get rooted

 

[Casuarina Head]

NAM is on an island with the strength of the 500/850mb winds. The globals continue to downtrend. This is going to be critical for tornado production.

What is the biggest possible reason for the downtrend?

 

[andyhb]

Impulse along the STJ in the models might be affecting the degree of LLJ response, would cause issues with the low level height gradient.

 

[Richardjacks]

Undeniable trend in the GFS

 

[Richardjacks]

Even the para GFS has backed off some, but not as dramatic

 

[Clancy]

SREF has a large corridor of high SigTor Ingredient parameters at 00Z Thursday.

 

[kcyalater]

Would very much appreciate the model trend downward to continue.

 

[MichelleH]

I *really* don't like it when Spann is this concerned.

 

[Richardjacks]

I think we have to keep in mind that the GFS could reverse course in the next 2 days...the nam could be right.

 

[GA Stormchaser]

I guess where at the max range of the SREF today. How does the SREF compare to the GFS at this range, or is that question not even valid?

I know the SPC uses the SREF, but they use every other model as well (I assume)


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[andyhb]

Euro looks like a mess.

 

[Casuarina Head]

I think we have to keep in mind that the GFS could reverse course in the next 2 days...the nam could be right.

There is a rather significant difference in the NHEM pattern between previous major outbreaks and this one. Of course, this was unlikely to be in the same league as those events on the left, but the STJ clearly is playing a bigger role this time. Do you see any indication that the global models would be more likely to revert to the NAM rather than vice versa? Anyway, I, too, hope that this event underperforms relative to its ceiling. The influence of the STJ would tend to limit the aerial coverage and duration of the SIGTOR threat, barring thermodynamic and mesoscale compensation.

 

[Brice Wood]

I’m worried for the towns that are still recovering from last years tragic outbreak

 

[Clancy]

The 18Z NAM didn't seem quite as aggressive as earlier runs.