Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

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Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#1 Postby TheProfessor » Wed Apr 08, 2020 4:18 am

I was waiting for SPC to highlight this before I created this thread and they just did so a few minutes ago.

Image


..DISCUSSION...
While considerable uncertainties remain, a substantial severe
episode appears possible this weekend, from Texas into portions of
the lower MS Valley on Saturday, and especially from the lower MS
Valley into portions of the Southeast on Sunday.

...D4/Saturday: Southern Plains into the Arklatex/Lower MS Valley...

Extended-range guidance continues to vary regarding the timing of
the ejecting cutoff low over the Southwest, though all solutions are
in generally good agreement in the development of a deep surface low
over the central/southern High Plains on Saturday as the upper low
ejects eastward. As low-level moisture streams northward, moderate
destabilization appears possible as far north as the Red River, as
deep-layer shear increases in advance of the ejecting trough. Severe
thunderstorm development will be possible during the
afternoon/evening across much of TX. Late Saturday night, an
increasing low-level jet may help to advect very rich low-level
moisture inland and potentially provide an additional focus for an
overnight severe thunderstorm threat from the TX Gulf Coast into the
lower MS Valley.

Image

...D5/Sunday: Arklatex/Lower MS Valley into the Southeast...

Timing differences continue among the extended-range guidance into
D5/Sunday, with the GFS notably faster, while the 08/00Z ECMWF has
trended slower compared to other guidance as well as its own
previous cycles. Regardless of timing, most guidance depicts the
ejecting trough as taking on a neutral to negative tilt, with a
deepening surface low moving into portions of the MS/TN Valleys.
While the northward extent of substantial destabilization remains
uncertain due to the potential for widespread convection, sufficient
instability and increasing low-level and deep-layer shear will
support a severe thunderstorm threat across much of the Southeast
throughout the day into Sunday night. If very rich low-level
moisture (low 70s dewpoints) over the Gulf can spread inland in
advance of this dynamic system, as depicted by recent ECMWF/UKMET
runs, then a substantial severe thunderstorm event could evolve,
with all hazards possible. Higher probabilities will be required if
guidance continues to trend in that direction.


I'll do my own detailed analysis of the 12z model suites tomorrow afternoon.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#2 Postby TheProfessor » Wed Apr 08, 2020 4:26 pm

I did my analysis in Powerpoint, everyone should be able to view the link.

https://1drv.ms/p/s!AhEAmF5OTC5egpJy933 ... Q?e=xa7x7v

Edit: Forgot to mention this is focused on the 12th, I haven't spent as much time analyzing the 11th.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#3 Postby TheProfessor » Thu Apr 09, 2020 2:53 am

SPC Day 3 Discussion:

...SUMMARY...
Severe thunderstorms will be possible across much of Texas into
portions of the lower Mississippi Valley, with the greatest threat
likely Saturday night into early Sunday morning. Large hail,
damaging wind, and perhaps a couple of tornadoes will be the primary
threats.

...Synopsis...
The persistent upper low over the Southwest is forecast to eject
eastward on Saturday, as a northern stream mid/upper-level trough
moves southeastward into the Northwest and northern Rockies.
Downstream, an upper ridge will develop over portions of the eastern
CONUS by Sunday morning in the wake of an upper trough moving over
the western Atlantic, which will allow the ejecting trough to take
on a more neutral tilt by the end of the period. At the surface, low
pressure is forecast to deepen over the central High Plains, to the
south of a cold front that will sweep across the northern High
Plains by Saturday evening.

...Much of TX into the lower MS Valley...
Rich low-level moisture over the western Gulf of Mexico is forecast
to begin spreading into portions of south into central TX at some
point Saturday/Saturday night, though this process could be delayed
somewhat depending on the influence of a lingering surface ridge
that will initially be in place along the Gulf Coast. While
surface-based destabilization may be limited during the day,
buoyancy is forecast to substantially increase Saturday night, as
steeper midlevel lapse rates associated with the ejecting trough
spread over much of TX amidst continued low-level moistening.

Elevated convection will likely erupt Saturday night across some
portion of west/central TX, with an initial hail threat. Some storms
may become rooted closer to the surface as they encounter greater
low-level moisture, with a corresponding threat of damaging wind and
perhaps a tornado or two given increasingly favorable wind profiles.
There will also be some potential for surface-based convection to
develop near the northward-moving warm front along the upper TX/LA
Gulf Coast prior to 12Z Sunday morning, which would pose a
conditional risk of all severe hazards.

Given the anticipated late timing of the higher-end severe
potential, 15% severe probabilities have been maintained for this
outlook, but there is some potential for higher probabilities once
details regarding low-level moisture return and the evolution of
late-night convection come into better focus.

...Northwest TX into central KS...
Modest low-level moisture that is transported into portions of west
TX on Friday will advect northward into a larger portion of the
southern/central Plains on Saturday. During the afternoon, moderate
instability may develop from northwest TX into central KS, as
dewpoints in the 50s F are advected northward beneath steep midlevel
lapse rates. Widely scattered thunderstorm development is possible
along a surface trough/dryline. While midlevel flow is forecast to
be only modest at best across this region by late afternoon, 25-35
kt of effective shear may support some storm organization with a
corresponding hail risk.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#4 Postby TheProfessor » Thu Apr 09, 2020 4:34 am

Here we go.


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

...DISCUSSION...
An outbreak of severe thunderstorms appears possible on Sunday
across parts of Louisiana, Mississippi, Alabama, and possibly into
Georgia by Sunday night. Tornadoes (potentially strong/long-tracked)
and widespread damaging winds are expected to be the primary
hazards.

...D4/Sunday: TX Gulf Coast eastward through the Southeast into the
Carolinas...
Ingredients for a potential severe thunderstorm outbreak appear
likely to come together Sunday into Sunday night. An ejecting
shortwave trough is forecast to take on a neutral to somewhat
negative tilt by Sunday afternoon as it moves quickly
east-northeastward across the Southeast states. Rich low-level
moisture will be drawn inland from the Gulf of Mexico in advance of
a deepening surface low that will move from the mid-MS Valley into
the Ohio Valley by Monday morning. Moderate destabilization in
conjunction with an 80-100 kt midlevel jet and 50-60 kt low-level
jet will result in a very favorable environment for organized
convection, including the potential for long-track supercells and a
corresponding strong tornado risk. Very strong low/midlevel flow
fields will also support widespread damaging wind potential.

Some uncertainty remains regarding the northward extent of the most
significant severe potential, given the presence of widespread
convection in advance of the ejecting shortwave. Guidance also
continues to trend slightly slower, with the GFS still a notably
fast outlier. A 30% probability contour has been introduced from LA
into central/southern MS/AL and southwest GA, where confidence is
highest in the outbreak potential at this time.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#5 Postby GeneratorPower » Thu Apr 09, 2020 1:34 pm

Looking forward to the detailed 12z EURO analysis.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#6 Postby TheProfessor » Thu Apr 09, 2020 2:15 pm

GeneratorPower wrote:Looking forward to the detailed 12z EURO analysis.


If you're looking forward to one from me then I probably won't do one today. But perhaps tomorrow I'll start doing a more detailed analysis with the 12z Mesoscale models as we get closer to being in NAM's wheelhouse.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#7 Postby GeneratorPower » Thu Apr 09, 2020 6:31 pm

TheProfessor wrote:
GeneratorPower wrote:Looking forward to the detailed 12z EURO analysis.


If you're looking forward to one from me then I probably won't do one today. But perhaps tomorrow I'll start doing a more detailed analysis with the 12z Mesoscale models as we get closer to being in NAM's wheelhouse.


Oh, I read your first post at the end...always enjoy reading analysis. Thank you!
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#8 Postby EF-5bigj » Thu Apr 09, 2020 7:59 pm

A lot of the soundings I'm seeing are alarming :eek: James Spann mentioned violent and long-tracked tornadoes
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#9 Postby HockeyTx82 » Thu Apr 09, 2020 10:35 pm

EF-5bigj wrote:A lot of the soundings I'm seeing are alarming :eek: James Spann mentioned violent and long-tracked tornadoes


Where specifically are you referring to? What day?
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#10 Postby TheProfessor » Thu Apr 09, 2020 10:37 pm

EF-5bigj wrote:A lot of the soundings I'm seeing are alarming :eek: James Spann mentioned violent and long-tracked tornadoes


Some of these SREF runs are going crazy with Sigtor. I think it's looking likely we'll at least see a day 1 high risk for southwest Mississippi.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#11 Postby TheProfessor » Thu Apr 09, 2020 10:38 pm

HockeyTx82 wrote:
EF-5bigj wrote:A lot of the soundings I'm seeing are alarming :eek: James Spann mentioned violent and long-tracked tornadoes


Where specifically are you referring to? What day?


This is for Sunday in the southeast. It's looking like the worst of the 2 days right now.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#12 Postby EF-5bigj » Thu Apr 09, 2020 11:51 pm

TheProfessor wrote:
HockeyTx82 wrote:
EF-5bigj wrote:A lot of the soundings I'm seeing are alarming :eek: James Spann mentioned violent and long-tracked tornadoes


Where specifically are you referring to? What day?


This is for Sunday in the southeast. It's looking like the worst of the 2 days right now.

Yep sunday a lot of PDS tornado soundings and backed winds also models are showing no morning convection.
Last edited by EF-5bigj on Thu Apr 09, 2020 11:58 pm, edited 1 time in total.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#13 Postby EF-5bigj » Thu Apr 09, 2020 11:57 pm

But we will know as it gets closer to the day Sunday dos look like the most dangerous day though.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#14 Postby Bunkertor » Fri Apr 10, 2020 4:01 am

TheProfessor wrote:
HockeyTx82 wrote:
EF-5bigj wrote:A lot of the soundings I'm seeing are alarming :eek: James Spann mentioned violent and long-tracked tornadoes


Where specifically are you referring to? What day?


This is for Sunday in the southeast. It's looking like the worst of the 2 days right now.


They look very spooky. What would be a good site for soundings, if i may ask ?
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#15 Postby TheProfessor » Fri Apr 10, 2020 4:30 am

Bunkertor wrote:
TheProfessor wrote:
HockeyTx82 wrote:
Where specifically are you referring to? What day?


This is for Sunday in the southeast. It's looking like the worst of the 2 days right now.


They look very spooky. What would be a good site for soundings, if i may ask ?


Sorry for the late reply, I've been without power for the last 6 hours. My favorite site for sounds is Pivotal Weather.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#16 Postby newtotex » Fri Apr 10, 2020 12:59 pm

I’m in Metro Birmingham, came on to see if anyone else had started a post! Listened to James Spann this morning and he seems to think it might be a big deal. This is normal for spring in Alabama


https://www.alabamawx.com/?p=208842
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#17 Postby Shell Mound » Fri Apr 10, 2020 2:03 pm

newtotex wrote:I’m in Metro Birmingham, came on to see if anyone else had started a post! Listened to James Spann this morning and he seems to think it might be a big deal. This is normal for spring in Alabama


https://www.alabamawx.com/?p=208842

The threat for a large-scale, violent outbreak à la 27 Apr 2011 still seems unlikely at this point. Even the potential for the Day-3 Moderate Risk to verify, at least insofar as strong, long-lived tornadoes are concerned, depends largely on mesoscale rather than synoptic features. For example, data from forecast soundings on the GFS/NAM suggest that activity may be predominantly linear with QLCS spin-ups, while the ECMWF suggests a narrow window for a few isolated (discrete) storms capable of producing long-tracked tornadoes. However, this is highly conditional and is directly related to the fact that the ECMWF narrowly extends the primary shortwave farther south than the GFS/NAM, which reinforces rather than hinders the Pacific cold front and induces veering of the winds with height, as opposed to veer-back-veer on the GFS/NAM. On the other hand, 27 Apr 2011 was much more obviously severe even on the synoptic scale. At this point, I wouldn’t be too aggressive in regard to tornadoes.

 https://twitter.com/CameronJNixon/status/1248627801420333056



 https://twitter.com/CameronJNixon/status/1248627802384912388



 https://twitter.com/CameronJNixon/status/1248627804297543682



 https://twitter.com/CameronJNixon/status/1248627806071934977



 https://twitter.com/CameronJNixon/status/1248627808823152641


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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#18 Postby Bunkertor » Fri Apr 10, 2020 5:49 pm

TheProfessor wrote:
Bunkertor wrote:They look very spooky. What would be a good site for soundings, if i may ask ?

Sorry for the late reply, I've been without power for the last 6 hours. My favorite site for sounds is Pivotal Weather.

Thanks very much. I did not have a sounding forecast site.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#19 Postby Bunkertor » Fri Apr 10, 2020 5:51 pm

Shell Mound wrote:The threat for a large-scale, violent outbreak à la 27 Apr 2011 still seems unlikely at this point. Even the potential for the Day-3 Moderate Risk to verify, at least insofar as strong, long-lived tornadoes are concerned, depends largely on mesoscale rather than synoptic features. For example, data from forecast soundings on the GFS/NAM suggest that activity may be predominantly linear with QLCS spin-ups, while the ECMWF suggests a narrow window for a few isolated (discrete) storms cap

And it seems, we have an early kick off time. Some say 13 z, which makes things more uncertain.
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Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020

#20 Postby newtotex » Fri Apr 10, 2020 6:28 pm

Shell Mound wrote:
newtotex wrote:I’m in Metro Birmingham, came on to see if anyone else had started a post! Listened to James Spann this morning and he seems to think it might be a big deal. This is normal for spring in Alabama


https://www.alabamawx.com/?p=208842

The threat for a large-scale, violent outbreak à la 27 Apr 2011 still seems unlikely at this point. Even the potential for the Day-3 Moderate Risk to verify, at least insofar as strong, long-lived tornadoes are concerned, depends largely on mesoscale rather than synoptic features. For example, data from forecast soundings on the GFS/NAM suggest that activity may be predominantly linear with QLCS spin-ups, while the ECMWF suggests a narrow window for a few isolated (discrete) storms capable of producing long-tracked tornadoes. However, this is highly conditional and is directly related to the fact that the ECMWF narrowly extends the primary shortwave farther south than the GFS/NAM, which reinforces rather than hinders the Pacific cold front and induces veering of the winds with height, as opposed to veer-back-veer on the GFS/NAM. On the other hand, 27 Apr 2011 was much more obviously severe even on the synoptic scale. At this point, I wouldn’t be too aggressive in regard to tornadoes.

https://twitter.com/CameronJNixon/status/1248627801420333056
https://twitter.com/CameronJNixon/status/1248627802384912388
https://twitter.com/CameronJNixon/status/1248627804297543682
https://twitter.com/CameronJNixon/status/1248627806071934977
https://twitter.com/CameronJNixon/status/1248627808823152641



Oh yea, definitely would not think that this would be anything like 4/27, I would imagine that’s an extremely rare event. But, you don’t have to have a huge outbreak to get a violent tornado. When I was a kid we had the April 8th F5 in western Birmingham and another F5 in Birmingham in the 1970’s neither of which were part of very big outbreaks IIRC?

Thanks for posting those graphics and the explanation! Will the thermodynamics be in place or is it looking iffy?
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