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Severe WX Wednesday/Thursday/Friday April 17th-19th Severe Threat (2 Viewers)


Messages
314
Location
jackson tennessee
Special Affiliations
SKYWARN® Volunteer
the 0z euro has a surface low in the tenn valley Thurs evening, would love to know if there is much ensemble support on that idea
the 0z euro has a surface low in the tenn valley Thurs evening, would love to know if there is much ensemble support on that idea
thats actually not the primary slp am I correct...? And that slp over Tennessee valley on the euro would be a secondary slp?
 

Richardjacks

Member
Meteorologist
Messages
492
Location
Hoover, Al
lots to be figured out at this point, but some of the models runs I have seen look very concerning. Assuming there isn't an issue with instability, I think the key is the 2nd vort max diving in. If it is slow enough it will cause the trough to become more broad based...opening the door for a large wide warm sector with plenty of expansive mid level shear....if there is low level shear too, in some ways, a classic April outbreak setup for the mid south/dixie...but again, there are still a lot of unknowns to be figured out yet.
 

Attachments

amp1998

Member
Messages
48
Location
Alabama
lots to be figured out at this point, but some of the models runs I have seen look very concerning. Assuming there isn't an issue with instability, I think the key is the 2nd vort max diving in. If it is slow enough it will cause the trough to become more broad based...opening the door for a large wide warm sector with plenty of expansive mid level shear....if there is low level shear too, in some ways, a classic April outbreak setup for the mid south/dixie...but again, there are still a lot of unknowns to be figured out yet.
That's a concerning look. I don't like that at all.
 

jmills

Member
Messages
105
Location
Troy, AL/Montevallo, AL
12z Euro is a dangerous look for the central Gulf states. I think it is underestimating surface temperatures (as a lot of synoptic models do at this range), It looks like it depicts a prefrontal trough/convergence axis and that is a concerning look, esp. this far out.
 

Fred Gossage

Member
PerryW Project Supporter
Messages
118
Location
Florence, AL
I will provide a word of caution preemptively in case this starts coming up in discussion in places:

Don't get too hung up on the surface low being pretty far to the north. Low-level winds are still backed way down in the warm sector, there are still significant surface pressure falls through the MS/AL/GA/TN portion of the warm sector, and the actual upper-level energy Thursday is more directly aimed here. To the thunderstorms, it still "feels" like the surface low is closer because of all that. They don't check the GFS, or Euro, to see what the surface low position is before they decide to rotate. We have had MANY outright violent tornado events over the decades here in Alabama with surface low positions a good bit north of what is considered that "classic" track from central Arkansas into Kentucky.
 

Richardjacks

Member
Meteorologist
Messages
492
Location
Hoover, Al
I will provide a word of caution preemptively in case this starts coming up in discussion in places:

Don't get too hung up on the surface low being pretty far to the north. Low-level winds are still backed way down in the warm sector, there are still significant surface pressure falls through the MS/AL/GA/TN portion of the warm sector, and the actual upper-level energy Thursday is more directly aimed here. To the thunderstorms, it still "feels" like the surface low is closer because of all that. They don't check the GFS, or Euro, to see what the surface low position is before they decide to rotate. We have had MANY outright violent tornado events over the decades here in Alabama with surface low positions a good bit north of what is considered that "classic" track from central Arkansas into Kentucky.
Fred, you are right on...we have seen plenty of severe events with the sfc low centered well away..there are several ways to get strong pressure falls and backing winds without the low being in your backyard.
 

Xenesthis

Member
Messages
247
Location
McMinnville TN
I will provide a word of caution preemptively in case this starts coming up in discussion in places:

Don't get too hung up on the surface low being pretty far to the north. Low-level winds are still backed way down in the warm sector, there are still significant surface pressure falls through the MS/AL/GA/TN portion of the warm sector, and the actual upper-level energy Thursday is more directly aimed here. To the thunderstorms, it still "feels" like the surface low is closer because of all that. They don't check the GFS, or Euro, to see what the surface low position is before they decide to rotate. We have had MANY outright violent tornado events over the decades here in Alabama with surface low positions a good bit north of what is considered that "classic" track from central Arkansas into Kentucky.
I concur entirely. I was alluding to that in prior posts. This feels like it could affect a lot of real estate and could be quite a significant event
 

MattW

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Messages
82
Location
Decatur, GA
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SKYWARN® Volunteer
HAM Callsign
KG4GUF
The timing slowed considerably since I last looked at it. Previously, it was looking to be a Wednesday afternoon threat for Georgia, but now seems to be Friday morning verbatim.
 

Equus

Member
Messages
714
Location
Saragossa, AL
I'm flying Bham-ATL-San Francisco Thursday starting at noon, so it's going to be interesting either way. Maybe will get some interesting aerial views of supercells if I luck into a window seat.
 
Messages
155
Location
Daleville, AL
Special Affiliations
NWS Tallahassee Discussion mentions possible 'Outbreak'.

.LONG TERM [Wednesday Night Through Monday]...

As multiple shortwaves superposition over the Southern Plains and
Lower Mississippi Valley, an anomalously deep longwave trough
will develop over the Deep South. This frontal system will be
stronger than this past weekends and will bring a high likelihood
of severe weather to the Southeast. Severe weather probabilities
based off of analog data are quite high across the Tri-State
region Thursday night, and SPC has steadily carried a Slight Risk
since this system appeared in their day 4-8 forecast. While the
exact timing, and placement of the highest threat for severe
weather is highly uncertain at this time, everyone should pay
close attention to the forecast over the next few days as the
chance of a severe weather `outbreak` across the Southeast is
increasing.
 

KoD

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Staff member
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PerryW Project Supporter
Messages
731
Location
Huntsville, AL
NWS HUN has a good write up for North Alabama on Thursday:

Looking at the severe threat, confidence remains low on how
significant the threat will be on Thursday. It seems the main
limiting factor will be very poor lapse rates between 700 mb and 500
mb during the main window of concern, likely due to the fact that
the upper trough remains positively to neutrally tilted and well to
our west for much of the afternoon. With that said, however, in the
days leading up to the system, southerly flow will be fairly
persistent and as it strengthens, dewpoints will climb into the lower
60s. Despite some shower activity in the morning, there should be
enough breaks in the cloud cover and strong enough WAA for temps to
climb into the mid 70s by the afternoon. This should provide
sufficient low level lapse rates during the afternoon and early
evening hours. But again, if the lower mid level lapse rates pan
out, it will greatly limit the severe threat. So, I`m not overly
confident that we will see the needed instability for an organized
severe threat. With that said, however, the wind profiles are
impressive as the low level jet intensifies as it crosses the
Mississippi River. The GFS and ECWMF are in fairly good agreement
that 850 mb winds increase as high as 60kts late Thursday afternoon
as showers and thunderstorms move into the area. As this occurs,
there may be a narrow window of steeper lapse rates as the upper
trough tries to become negatively tilted and this would lend us some
moderate instability. Certainly not a slam dunk scenario, however
there is enough chance for severe weather that we will mention it in
the HWO Thursday afternoon and evening.
 

Kory

Member
Messages
2,516
Location
Tuscaloosa, Alabama
This past system had 5.0-5.5 C/KM lapse rates and we were still able to manage ~1,000 J/KG SBCAPE in the dead of night. I'm not sure it'll be as big of a limiting factor as they believe.

My concern is some backing of the winds in the mid levels if this amplifies anymore. But right now, this continues to be a substantial threat.
 

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