Severe WX Severe Threat 17-18 March 2021

[Bama Ravens]

...Lower MS Valley into AL/GA...

Multiple rounds of intense, severe convection will be possible,
mainly across MS/AL on Wednesday afternoon into the overnight hours.
Convection will intensify along the eastward progressing cold front
across central and eastern AR/LA during the late morning/afternoon
as it encounters effective shear greater than 60 kt, MLCAPE around
1500-2500 J/kg and midlevel lapse rates around 7-8 C/km. Fast storm
motion, with 925-700 mb flow greater than 40 kt will support
widespread damaging gusts with some gusts greater than 65 kt
expected. Large hail (some greater than 2 inch in diameter,
especially from the AR/MO border into northern LA, southwest TN and
northern/central MS) is also expected with this activity.

Further east across northeast LA into MS and AL a more concerning
scenario appears possible. Most forecast guidance agrees that a
round of afternoon thunderstorms are expected. This activity is
expected to develop in weaker ascent, driven by heating and low
level warm advection. Strong 0-3 km shear near 30-40 kt will already
be in place with enlarged low level hodographs evident. Given weaker
forcing, this activity will have an opportunity to remain more
discrete and any cell will quickly become a supercell capable of
producing strong tornadoes. As a 40-50 kt low level jet increases
around 00-03z, intense supercells are expected to advance eastward
along with the cold front across MS and into AL overnight. This will
bring a second round of significant severe storms capable of intense
tornadoes, large hail and intense damaging winds across much of
MS/AL. If these trends are maintained, an upgrade to a High risk
could be necessary with the initial Day 1
Convective Outlook at 06z
tonight.

 

[Kory]

Add in the UKMET into the group that doesn’t agree with the NAM and a weaker LLJ...even prior to 00z. That idea seems to be on an island from the data I’ve looked at.

Add in the Euro now. It looks a bit stronger with the LLJ earlier.

 

[Fred Gossage]

Add in the Euro now. It looks a bit stronger with the LLJ earlier.

50 kt in south MS at 18z that is coming north, and faster at developing 50kt over central AL at 00z. This changes things.

 

[Jack16]

A purpose-built tornado shelter, or a location such as a school or church designated as a shelter? I have exactly 1 purpose-built shelter within 25 miles of me. Georgia has a severe lack of shelters.

Local governments across Georgia find great liability in building shelters. Not so much with relation to people taking shelter in them, but as to what happens to them between storms....homeless, drug use, all types of bad stuff.

 

[Tanner]

I like what James Spann says.... if there is one tornado tomorrow, and it comes down your street..... it’s is YOUR April 27.


Sent from my iPhone using Tapatalk

I live in Western Massachusetts. We had a high-end, long-track EF3 move through the area back on June 1st, 2011. And to say it felt like what you just said was an understatement. I had never seen such devastation, especially in my home area. So Spann is 100% right. Okay, enough of that, let's get on track with the threat tomorrow. I'm new here btw, so hello!

 

[Jetstream]

I live in Western Massachusetts. We had a high-end, long-track EF3 move through the area back on June 1st, 2011. And to say it felt like what you just said was an understatement. I had never seen such devastation, especially in my home area. So Spann is 100% right. Okay, enough of that, let's get on track with the threat tomorrow. I'm new here btw, so hello!

Hello Tanner, and welcome to talkweather!

 

[Whyrob1998]

I think the High risk area will be where MS AR and TN meet will be under a high risk. STP is around 3.4 in spots. Especially around Columbus, MS and AR

 

[Jack16]

As a practicing emergency manager for 39 years every severe weather episode is taken seriously. No one can determine how many structures will be damaged, people injured or impacts to infrastructure. April 27, 2011, April 3-4, 1974, November 21, 1992, April 3, 2000, March 27, 1994, April 11, 1965, all big days for those who were impacted.

 

[Brice Wood]

Fred, is they were to issue a high risk, where would you most likely see that to be at?

 

[Fred Gossage]

Fred, is they were to issue a high risk, where would you most likely see that to be at?

Their discussion is focusing on much of MS/AL for the highest threat.

 

[Ingyball]

I wanted to share a post made by a meteorologist I know from another forum as it's great analysis as to why we may see a high risk tomorrow.

"
I’ve kinda mentioned this either directly or indirectly... but you need a big window of opportunity for significant tornadoes to get a high risk. 1 to 2 days ago we didn’t really know if that was gonna happen because we didn’t have much confidence about storm mode; will there be warm sector cells? What will the frontal storm mode be like? Etc.

But now that the CAMs are in range, we’re seeing a distinct chance for warm sector supercells AND semi-discrete cells along the front AND that it looks like the front will continue to produce tornadic supercells through the night.

For the current moderate risk, there are 2 rounds of tornadic storms. The afternoon round of warm sector supercells, then the frontal storms in the evening and overnight. So for the moderate risk it looks like there’s gonna be a 6+ hour window of opportunity for tornadic supercells. That’s more than enough to check off the duration aspect.

2 rounds of tornadic storms means 2 chances for the moderate risk to verify... if we can see some consistency where warm sector supercells are most likely, confidence in seeing a tornado warning in that area essentially doubles. Hence, SPC would feel comfortable increasing the probabilities."

However, one thing that would throw a wrench in this is the warm sector having higher shear than expected. If that happened then all the sudden the warm sector storms would be worthy of a high risk on their own. If the LLJ is stronger and arrives earlier than expected, then that spells trouble.

 

[Fred Gossage]

I wanted to share a post made by a meteorologist I know from another forum as it's great analysis as to why we may see a high risk tomorrow.

"
I’ve kinda mentioned this either directly or indirectly... but you need a big window of opportunity for significant tornadoes to get a high risk. 1 to 2 days ago we didn’t really know if that was gonna happen because we didn’t have much confidence about storm mode; will there be warm sector cells? What will the frontal storm mode be like? Etc.

But now that the CAMs are in range, we’re seeing a distinct chance for warm sector supercells AND semi-discrete cells along the front AND that it looks like the front will continue to produce tornadic supercells through the night.

For the current moderate risk, there are 2 rounds of tornadic storms. The afternoon round of warm sector supercells, then the frontal storms in the evening and overnight. So for the moderate risk it looks like there’s gonna be a 6+ hour window of opportunity for tornadic supercells. That’s more than enough to check off the duration aspect.

2 rounds of tornadic storms means 2 chances for the moderate risk to verify... if we can see some consistency where warm sector supercells are most likely, confidence in seeing a tornado warning in that area essentially doubles. Hence, SPC would feel comfortable increasing the probabilities."

However, one thing that would throw a wrench in this is the warm sector having higher shear than expected. If that happened then all the sudden the warm sector storms would be worthy of a high risk on their own. If the LLJ is stronger and arrives earlier than expected, then that spells trouble.

If the Euro and UKMET trends are right, that specific thing is happening now. 0-1 km bulk shear of 40-50 kts in east MS/west AL by 21z, widespread through central AL by 00z. 40-50 kts in the 0-1 km layer is supportive of violent tornadoes with cool season instability. That's getting juxtaposed in time when the CAPE will be 2000+...

 

[Richardjacks]

If the Euro and UKMET trends are right, that specific thing is happening now. 0-1 km bulk shear of 40-50 kts in east MS/west AL by 21z, widespread through central AL by 00z. 40-50 kts in the 0-1 km layer is supportive of violent tornadoes with cool season instability. That's getting juxtaposed in time when the CAPE will be 2000+...

I was thinking the very same thing. This is not a case of waiting for instability, it is a case of when shear arrives. The earlier, the greater chance of significant tornadoes

 

[Evan]

I was thinking the very same thing. This is not a case of waiting for instability, it is a case of when shear arrives. The earlier, the greater chance of significant tornadoes

Yep. And the Euro is definitely showing that. Let's see if the 18z NAM is still on an island. If it caves to the faster arrival of shear and backs off the wedge then I definitely think a high risk is going to be in the cards.

 

[TH2002]

While there's no telling for sure I see a pretty decent probability of an upgrade to a High Risk area by late tonight or early tomorrow morning.

 

[Richardjacks]

The HRRR 18z...
The makings of a high risk day especially for central/north Miss and Ala.

 

[Justin Hindman]

While there's no telling for sure I see a pretty decent probability of an upgrade to a High Risk area by late tonight or early tomorrow morning.

High risk is possible. I would say this is the biggest potential since April 28, 2014. Whether it goes high risk or not it really doesn’t matter, it’s going to be a nasty day and night for many

 

[TornadoFan]

The HRRR 18z...

View attachment 6987





View attachment 6986

Not a good thing, I take it?

 

[Clancy]

FFC released a briefing for the upcoming storm. They mention the potential for a strong tornado or two.

 

[KoD]

The HRRR 18z...
The makings of a high risk day especially for central/north Miss and Ala.
View attachment 6987





View attachment 6986

Yikes....