March 17-18 Severe Weather Event

[DanLarsen34]

Hi all, 

Thought that I would get a thread going for this coming Wednesday.
 

Models are starting to show a potentially volatile scenario across Mississippi and Alabama. The SPC just issued a broad 15% risk area in their day 5 outlook and mentioned that greater probabilities may be needed in later outlooks. James Spann is also bringing attention to this set-up, mentioning that a significant severe weather event with violent tornadoes is possible in his latest write-up about Wednesday. https://www.alabamawx.com/?p=224731

[crossbowftw3]

Some vbv exists in the soundings but the broad-brush potential of this event cannot be understated. 

[Cheeznado]

I have been looking at this for a few days now,  will probably be my first storm chase in over a year.

[Ground Scouring]

I think this event will end up verifying on the “low” side of current expectations. The two most recent GFS runs have shifted toward a higher-amplitude, blockier setup due to their resolving the situation in the North Pacific (Gulf of Alaska) better. This means that the downstream circulation over the Ozark region will have a tendency to become “pinched” due to enhanced shortwave ridging over the Great Lakes. In turn, this implies a surging cold front along with mid-level winds paralleling the surface boundary, especially toward the northern half of the warm sector. I think we may see a few supercells capable of producing a couple of strong tornadoes, but these will likely be localised along boundaries from eastern MS eastward across the southern two-thirds of AL. Most of this event should consist of QLCS and bows, with some isolated, discrete events along boundaries, as mentioned. One thing I have noticed is that “major” events since 2011–13 have ended up underperforming in terms of either severity and/or aerial coverage, perhaps due to the warming Pacific basin, the slowing AMOC, and the +PMM signature; the warmer Pacific basin and emergent -AMO over time have tended to hinder low-amplitude, progressive setups, regardless of temporary shifts toward -ENSO/-PDO.

[buckeyefan1]

On 2/27/2021 at 6:44 PM, buckeyefan1 said:

Seriously though, mid March is looking interesting for a severe threat somewhere in the south   

And here we are  

[jburns]

10 hours ago, crossbowftw3 said:

Some vbv exists in the soundings but the broad-brush potential of this event cannot be understated. 

Hmm.  It doesn’t exist?

[DanLarsen34]

New outlook from the SPC overnight raised probabilities to 30% in the Day 4 outlook on Wednesday across most of Mississippi and Alabama. Their confidence is quite high at this range regarding the potential for a major severe weather event: 

 

“

On Wednesday, convection will likely be ongoing across the eastern
   Texas/Arkansas/Louisiana areas, with some severe risk possible
   during the morning hours.  By afternoon, an increase in coverage and
   intensity is expected as closed upper system shifts out of the
   Plains toward the Mississippi Valley.  With a rather
   large/destabilizing warm sector and ample shear across a broad
   region, a rather large 15% area will be maintained, representative
   of an all-hazards severe risk.  Corridors of greater risk --
   including possibly more concentrated tornado potential -- may evolve
   during the afternoon, possibly near the northward-moving warm front.
    While the ECMWF is farther south with this west-to-east front
   (central MS/AL) during the afternoon than the GFS (southern TN),
   will nonetheless introduce a 30% risk area -- encompassing a range
   of possible warm-frontal locations -- given likelihood for
   widespread severe weather that warrants greater probability at this
   time.  ”

[Cheeznado]

This NAM sounding from the KTCL area is about as textbook for tornadoes as you can get.

[crossbowftw3]

This is a dizzyingly wide warm sector on the NAM

[janetjanet998]

 

[MattPetrulli]

SREF already at 60 for 00z Thursday.

[wizard021]

1 hour ago, MattPetrulli said:

SREF already at 60 for 00z Thursday.

Cmc very slow moving upper low and it arrives Wed night . This supports weak ll shear.  Marginal slight risk warranted mainly for large hail.

[wizard021]

If it speeds up the upper jet is fairly weak. The low level wind response will not result in a big outbreak. Ceiling is 10 percent locally in backed wind along wf.

[wizard021]

https://www.tropicaltidbits.com/analysis/models/?model=gem&region=us&pkg=uv250 as modeled you will see a clustering of hail with large cape and lapse rates and 40 to 50kt 06km shear .  Low level shear generally weak 850 to 700mb.  Gfs and nam too fast as always. 

[Misstertwister]

Hey all. I come on here for weather updates. I am learning how to read analogs. However, I’ve got a business trip coming up in New Orleans and ill be driving in from East Texas Wednesday and arriving in NO Wednesday afternoon. Is this more of an AL/MS event or Louisiana/NO also?

 

ill obviously be watching the SPc next few days but does travel and stay in NO look alright for Wednesday?

[CheeselandSkies]

9 hours ago, Misstertwister said:

Hey all. I come on here for weather updates. I am learning how to read analogs. However, I’ve got a business trip coming up in New Orleans and ill be driving in from East Texas Wednesday and arriving in NO Wednesday afternoon. Is this more of an AL/MS event or Louisiana/NO also?

 

ill obviously be watching the SPc next few days but does travel and stay in NO look alright for Wednesday?

SPC's Day 3 Enhanced risk clips the northeast corner of Louisiana, with the New Orleans area in the slight risk.

You'd probably be OK to travel but definitely stay weather aware.

[eyewall]

I think we may need to add Thursday to this thread too but definitely the first big Dixie Alley event of the year.

[Orangeburgwx]

I think we may need to add Thursday to this thread too but definitely the first big Dixie Alley event of the year.

Indeed so, 12z NAM absolutely smashes central South Carolina on Thursday

 

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[PackGrad05]

12 minutes ago, Orangeburgwx said:

Indeed so, 12z NAM absolutely smashes central South Carolina on Thursday

 

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Which NAM product are you looking at?  

[wizard021]

Yes Thursday looks like the bigger day .

[Orangeburgwx]

Which NAM product are you looking at?  

Pivotal

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[Bob's Burgers]

[PackGrad05]

NAM shows a good amount of 0-3km helicity over NC on Thursday...  Sig Tor Parameter around 1-2. .  Limiting factor appears to be instability...  progression of warm front and time of day will play big.

[Orangeburgwx]

NAM shows a good amount of 0-3km helicity over NC on Thursday...  Sig Tor Parameter around 1-2. .  Limiting factor appears to be instability...  progression of warm front and time of day will play big.

Each of the last 4 runs have slowed down the progression

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[Orangeburgwx]

The very definition of weather porn:

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[magpiemaniac]

[hlcater]

Of course I check in here and see someone posting the GFDL C-Shield lol.

[janetjanet998]

UM...

 

[brianc33710]

5 hours ago, magpiemaniac said:

Will the SPC consider upgrading this to a "Moderate Risk"? The parameters seem pretty scary. I WON'T hold out for a "High" risk. We didn't even get that for the Easter 2020 Tornado Outbreak. 

EDIT: JP Dice on FOX 6 says winds & large hail are the greatest threats. James Spann on ABC 33/40 forecasts tornadoes as our biggest threat. Spann seems to think the SPC will raise us to a Moderate at some point. I just don't know when to expect the SPC's next update.

[magpiemaniac]

18 minutes ago, brianc33710 said:

Will the SPC consider upgrading this to a "Moderate Risk"? The parameters seem pretty scary. I WON'T hold out for a "High" risk. We didn't even get that for the Easter 2020 Tornado Outbreak. 

EDIT: JP Dice on FOX 6 says winds & large hail are the greatest threats. James Spann on ABC 33/40 forecasts tornadoes as our biggest threat. Spann seems to think the SPC will raise us to a Moderate at some point. I just don't know when to expect the SPC's next update.

The next update should come out at 0730 UTC or 2:30 AM CDT.