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Tn Valley Severe Weather


jaxjagman
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I DO NOT know as much about severe as most, but I will say it looks like the shortwave is pretty long and the best dynamics seem to be with the northern end of it (red circle), while the lower end (purpleish circle) is what will swing through tonight and cause a second surge of heavy precip. 

 

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Radar loop @Holston_River_Rambler shared on the previous page still has validity. Some other CAMs have shown it off and on. Central Alabama!

Gulf front was reinforced last night by outflow OFB from showers yesterday. It is lifting northward in Alabama. While some sort of east-west boundary made it to northwest Alabama, differential heating/dews is evident central Alabama. Prefrontal convergence is also ahead of the main front - Alabama Mississippi border as usual.

As for the positive tilt, it probably mitigates some risk. Enhanced is right. No MDT today. Also the LLJ is lifting away, which could keep even central Bama in check. However I always watch boundary intersections out ahead of the synoptic ones.

All that said, with greater instability, positive tilt can go in the South and Ohio Valley. Plains is more fickle needing neutral due to dewpoint trajectories. Here southwest is still moist flow. 

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Yes if those storms inflow does not get disrupted by central Alabama activity, they are near the other lifting boundary I wrote of at about now near the River. Prefrontal trough is also there near Corinth MS into Tenn, ahead of the main front. It's a boundary intersection.

Also possible the north (Tenn Miss) and south (cental Bama) coexist with the SSW LLJ vs one from the SSE. Again central Bama has the intersection of pre-trough convergence and Gulf front/OFB.

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Notes from my chase to Tennessee City today. That TVS was trying it's best but fell apart as I approached it. A defined lowering yes...but surface winds were just so weak. Really the most notable feature was the ground-to-cloud lightning. There was plenty of it out that way. I'll post some footage later because whatever hail shaft/wall cloud I encountered was worth the trip.

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Next week might be interesting

 

 Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0358 AM CST Sun Feb 26 2023

   Valid 011200Z - 061200Z

   ...SEVERE WEATHER OUTBREAK POSSIBLE ON D5/THU...

   ...DISCUSSION...
   ...Wednesday/Day 4...
   West-southwest mid-level flow will be in place on Wednesday as
   moisture advection occurs across much of the Southeast.
   Thunderstorms will be possible across the moist sector from east
   Texas eastward across the Gulf Coast states and northward into the
   mid Mississippi Valley. At this time, any severe threat is expected
   to remain isolated on Wednesday, due to weak instability and limited
   large-scale ascent.

   ...Thursday/Day 5 and Friday/Day 6...
   An upper-level trough will move quickly eastward on Thursday from
   the Desert Southwest into the southern Plains. By late afternoon on
   Thursday, model forecasts develop a corridor of moderate instability
   in east Texas and have strong deep-layer shear present over much of
   the southern Plains. This environment should support severe storms
   capable of large hail, wind damage and perhaps some tornadoes. A
   widespread outbreak of severe weather will be possible beginning
   Thursday afternoon and continuing into the overnight period. The
   potential for severe storms should shift eastward across the lower
   to mid Mississippi Valley and into the central Gulf Coast states
   Thursday night where the threat for wind damage, hail and tornadoes
   should continue.

   On Friday, the upper-level system is forecast to move northeastward
   across the Ohio and Tennessee Valleys. The greatest potential for
   severe storms would be from eastern parts of the southeastern states
   northeastward into the Carolinas. Any line of storms that can
   persist or develop during the day on Friday, could have wind-damage
   or tornado potential. However, the overall threat on Friday should
   be less than Thursday, as the upper-level trough moves further
   northeast away from the stronger instability.

   ...Saturday/Day 7 and Sunday/Day 8...
   On Saturday and Sunday, high pressure is forecast to settle in
   across much of the continental United States. This dry and cool
   airmass should make thunderstorm development unfavorable in most
   areas.

   ..Broyles.. 02/26/2023
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NWS Storm Prediction Center Norman OK
   0359 AM CST Mon Feb 27 2023

   Valid 021200Z - 071200Z

   ...SEVERE WEATHER OUTBREAK POSSIBLE ON D4/THU...

   ...DISCUSSION...
   ...Thursday/Day 4...
   A regional outbreak of severe weather appears increasingly likely
   Thursday afternoon and Thursday night including the potential for
   large hail, damaging winds, and tornadoes, some of which may be
   strong. Available guidance is in ample general agreement with the
   east/northeastward-ejection of an upper trough from the southern
   Rockies early Thursday to the Ozarks/ArkLaTex by late Thursday
   night. Owing to a stalling/decaying front early this week,
   respectable low-level moisture will exist across much of the Deep
   South in advance of this approaching upper-level system and its
   related intense deep-layer wind field. Current thinking is that this
   severe potential should steadily increase across central/eastern
   Texas and possibly southeast Oklahoma during the day. This risk
   should only increase/further organize into Thursday evening across
   the ArkLaTex/ArkLaMiss and Lower Mississippi Valley, and eventually
   the Tennessee Valley late Thursday night.

   ...Friday/Day 5...
   Severe-weather potential is expected to continue to Friday across
   the Southeast States including Georgia/north Florida and the
   Carolinas, and possibly as far north as parts of the Mid-Atlantic.
   This will be as the upper-level trough races northeastward from the
   Lower Mississippi Valley toward the Ohio Valley/Mid-Atlantic States.
   Very strong deep-layer winds will coincide with a modestly unstable
   warm sector ahead of a cold front and/or residual convection from
   Thursday night. Damaging winds and a few tornadoes could occur
   across the region.

   ...Saturday/Day 6 through Monday/Day 8...
   An inactive few days with limited deep convective/severe potential
   is currently expected this weekend into early next week. High
   pressure will likely be increasingly established east of the Rockies
   as richer low-level moisture is shunted toward the Gulf of Mexico.

   ..Guyer.. 02/27/2023
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The pivot from a positive to negative tilt sets up over Ark and northern La Thursday afternoon. If trends continue, I think this could be a major outbreak. Friday doesn’t look as bad as the trough ejects NW of the area but the warm sector will be bigger and ETn will be close to the right exit of the jet. On the other side, widespread rains could greatly reduce instability. I do think this has the potential to be significant, especially Thursday afternoon into Thursday night.


.

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2 hours ago, PowellVolz said:

The pivot from a positive to negative tilt sets up over Ark and northern La Thursday afternoon. If trends continue, I think this could be a major outbreak. Friday doesn’t look as bad as the trough ejects NW of the area but the warm sector will be bigger and ETn will be close to the right exit of the jet. On the other side, widespread rains could greatly reduce instability. I do think this has the potential to be significant, especially Thursday afternoon into Thursday night.


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I read where TN is not included in any big severe that it should stay south of TN.  Flooding is another story.  That’s what I’ve read.  

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MRX on Thursday/Friday.


“Thursday night into Friday, the closed low will become increasingly
negatively tilted as it moves towards Arkansas, then north of the
Ohio River Valley. The expectation is for this to be a very dynamic
system with MSLP at the center of the surface low dropping to 980mb
or less with uncertainty remaining in the exact track. With a broad
warm sector, strong upper dynamics, and impressive LLJ, this system
will likely produce notable severe weather across at least some
portion of the southeastern U.S. with limited confidence on the
exact impacts locally. A lot of this will depend on how quickly the
system will occlude, i.e. the surface warm sector reaching our area.
The most recent GFS and ensemble mean have both trended further
north, suggesting greater potential for occlusion as it reaches the
area. The ECMWF, however, brings the warm sector well into the
region. Nonetheless, the impressive MSLP gradient and 850mb jet both
illustrate likelihood of a notable mountain wave event and gusty
winds across the region. This system is certainly something to watch
for additional rainfall and strong winds at a minimum with remaining
uncertainty for organized severe convection locally. Afterwards,
cooler air will funnel into the area with expanding high pressure
leading to a drier trend through the weekend”


.

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Tonight could be dicey in the Mid-South. Ingredients are there as a LLJ interacts with warm front. Mess mode could be a saver overnight.

Thursday daylight is mainly an Arkansas (and points southwest) event. However an organized squall line QLCS should slam into the Mid-South late Thursday night. Line survives into Friday morning...

Key to Friday is the LLJ hanging around long enough. Some NWP ejects the backed part of it in a hurry, which would still leave a line of thunderstorms and straight line wind. Low and mid-level winds remain strong all day Friday, which would support severe. 

Tornado question has a lot to do with if the backed portion of the LLJ remains in East Tennessee and North Georgia into Friday afternoon. I'm not sure for what I wish. Chaser on a Friday. Keep family safe any day. My gut says just wind East Tenn. Makes it a moot point.

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Tonight could be dicey in the Mid-South. Ingredients are there as a LLJ interacts with warm front. Mess mode could be a saver overnight.
Thursday daylight is mainly an Arkansas (and points southwest) event. However an organized squall line QLCS should slam into the Mid-South late Thursday night. Line survives into Friday morning...
Key to Friday is the LLJ hanging around long enough. Some NWP ejects the backed part of it in a hurry, which would still leave a line of thunderstorms and straight line wind. Low and mid-level winds remain strong all day Friday, which would support severe. 
Tornado question has a lot to do with if the backed portion of the LLJ remains in East Tennessee and North Georgia into Friday afternoon. I'm not sure for what I wish. Chaser on a Friday. Keep family safe any day. My gut says just wind East Tenn. Makes it a moot point.
Work is going to be fun in the morning. The weather alarm went off so many times and kept waking us up. The tornado warning is what got us out of bed. Warning has expired now but work alarm is set for 3:45a.m. I can't wait.

Sent from my moto z4 using Tapatalk


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If ETn gets a little sunshine on Friday it could get interesting. We don’t typically get surface winds out of the South to SE with a strong low pressure a couple hundred miles to our NW. whether we get a tornado or not, straight line winds are going to be a issue and I won’t be surprised if SPC goes with a enhanced across ETn just for that. MRX is thinking they might go with a high wind warning for the valley and I can’t remember that ever being issued.


.

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