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Severe Severe threat February 24th (1 Viewer)

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#2
Here's the related 2/19 Outlook and Discussion from SPC.

Weather.gif

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0358 AM CST Mon Feb 19 2018

Valid 221200Z - 271200Z

...DISCUSSION...
Better agreement/consistency is evident at this time with respect to
various medium-range model runs through a majority of the day 4-8
period, as compared to 24 hours prior. Models in general depict
that a major short-wave trough -- digging across California and the
Great Basin day 4 (Thursday) will eject east across the Desert
Southwest/southern Rockies day 5, and then the central and southern
Plains day 6 (Saturday). While this feature is progged to
weaken/deamplify with time due to persistence of southeastern U.S.
ridging, surface lee cyclogenesis is expected over the southern High
Plains early in the day which will deepen/shift quickly
east-northeast into the Ohio Valley/Midwest overnight. Ahead of
this system, low-level moisture return from the Gulf of Mexico
should prove sufficient for at least some warm-sector CAPE
development which -- combined with what should be a favorable
background lower- and middle-tropospheric wind field -- suggests
that some severe weather risk may evolve Saturday. While degree of
instability may limit risk to some degree, ample evidence exists to
suggest initial introduction of 15% severe weather probability from
the Arklatex vicinity east across parts of the lower Mississippi and
into the Tennessee Valleys.

As the weakening upper system shifts quickly east-northeast across
the lower Great Lakes region day 7 (Sunday), expect the trailing
surface front to weaken and become oriented increasingly
west-to-east across the Gulf Coast region, suggestive of diminished
severe potential. In addition, model differences increasing through
the end of the period result in reduced confidence with respect to
the convective forecast through early next week.
 
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#4
2/20 Outlook and Discussion from SPC:

Severe.gif


Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0337 AM CST Tue Feb 20 2018

Valid 231200Z - 281200Z

...DISCUSSION...
Model consensus is that a significant shortwave trough will eject
northeast through the central Plains and middle MS Valley region
(Day 5) Saturday and Saturday night. Some deamplification of this
feature is expected, but model differences persist. GFS maintains a
more amplified trough with a deeper surface low suggesting the
potential for a greater severe threat compared to ECMWF, UKMET and
the Canadian. In either case a few severe storms might evolve in
vicinity of frontal zone from east TX into the lower MS and TN
Valley region as the low-level jet strengthens and shifts northeast
in response to the approaching shortwave trough. Storms may be
ongoing along baroclinic zone over a portion of this region, with
potential to intensify within zone of modest destabilization and
forcing associated with the migrating low-level jet. Limiting
factors are likelihood of widespread clouds and tendency for the
approaching shortwave trough to weaken with deeper forcing likely
remaining northwest of warm sector.

Some severe threat might linger into day 6, but overall potential
should decrease later day 6 into day 7 as a cold front moves into
the northern Gulf coast area.
 
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#7
The overall setup looks worthy of an enhanced risk of severe weather in parts of Arkalatex and lower MS valley with marginal mid-level lapse rates amidst a fairly unstable and moist boundary layer and modest bulk shear of 45-60 KT (if it becomes too strong could potentially be a detriment to severe in this case), and SRH of >150-300 m2/s2 that favors multicellular clusters and/or isolated supercells capable of producing damaging winds, hail, and isolated tornadoes. Certainly worth watching in north-central Louisiana, eastern Texas, southeastern Oklahoma, Arkansas, north-central Mississippi and southwestern Tennessee. The one limiting factor will be the most favorable synoptic-scale mid-upper level forcing remaining far removed from the best instability further south (as indicated by the stronger Q-vector convergence (in red) over the mid-MS Valley)
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#8
The overall setup looks worthy of an enhanced risk of severe weather in parts of Arkalatex and lower MS valley with marginal mid-level lapse rates amidst a fairly unstable and moist boundary layer and modest bulk shear of 45-60 KT (if it becomes too strong could potentially be a detriment to severe in this case), and SRH of >150-300 m2/s2 that favors multicellular clusters and/or isolated supercells capable of producing damaging winds, hail, and isolated tornadoes. Certainly worth watching in north-central Louisiana, eastern Texas, southeastern Oklahoma, Arkansas, north-central Mississippi and southwestern Tennessee. The one limiting factor will be the most favorable synoptic-scale mid-upper level forcing remaining far removed from the best instability further south (as indicated by the stronger Q-vector convergence (in red) over the mid-MS Valley)
View attachment 4123
View attachment 4119
View attachment 4122
View attachment 4120
View attachment 4121
Webber, are you thinking this will be a late afternoon/evening setup if it does materialize?
 
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#14
2/21 Outlook and Discussion from SPC

day4prob.gif

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0356 AM CST Wed Feb 21 2018

Valid 241200Z - 011200Z

...DISCUSSION...
A significant shortwave trough will eject northeast through the
central Plains and middle MS Valley region (Day 4) Saturday and
Saturday night. Some deamplification is expected, but the trough
will take on a more negative tilt as it approaches the middle MS
Valley. GFS is still the stronger solution with deeper cyclogenesis
and suggests potential for a slightly more robust severe threat. In
either case a forced line of potentially strong to severe storms
might evolve in vicinity of cold front initially over northeast TX,
before spreading into the lower MS and TN Valley regions as the
low-level jet strengthens and shifts northeast through moistening
warm sector. While vertical shear and overall character of the wind
profiles should be more than adequate for organized severe storms,
primary limiting factor appears to be a marginal thermodynamic
environment given likelihood of widespread clouds and weak lapse
rates.

Some severe threat might linger into Sunday (day 5) over a portion
of the Middle Atlantic, but confidence is not high enough at this
time to introduce a categorical area. Overall severe potential
should remain low day 6 into day 7 as a cold front settles into the
northern Gulf coastal area.
 
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#18
2/22 Outlook and Discussion from SPC.
Possible upgrades in later Outlooks.

day3otlk_0830.gif

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0219 AM CST Thu Feb 22 2018

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM A PORTION OF
EAST TEXAS INTO THE LOWER MISSISSIPPI...TENNESSEE AND OHIO
VALLEYS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
OF THE SOUTHERN PLAINS THROUGH THE OHIO VALLEY AND SOUTHEAST
STATES...

...SUMMARY...
Strong to severe storms will be possible Saturday from a portion of
northeast Texas through the lower Mississippi, Tennessee and Ohio
Valleys.

...Northeast TX into the lower Mississippi Tennessee and Ohio
Valleys...

A significant shortwave trough will eject northeast through the
central Plains and middle to upper MS Valley region Saturday and
Saturday night while taking on a negative tilt. In response to
forcing accompanying this feature, a surface low initially over the
southern Plains will deepen as it develops northeast through the
middle MS Valley, eventually reaching the Great Lakes toward the end
of the period. Warm front extending east from the surface low will
move northward, reaching the OH Valley Saturday night. A cold front
initially across west TX will advance through the Southern Plains
and middle to lower MS Valley during the day reaching the OH and TN
Valleys Saturday night. A strengthening low-level jet resulting from
the deepening cyclone will transport richer gulf moisture northward
with low 60s F dewpoints as far as the OH Valley and mid to upper
60s from east TX to the lower MS Valley. However, instability will
probably remain marginal due to widespread clouds and modest lapse
rates with MLCAPE likely to remain below 1000 J/kg over most of the
warm sector.

A forced line of potentially strong to severe storms should evolve
in vicinity of cold front initially over north central or northeast
TX into southeast OK during the day. Activity will subsequently move
into the lower MS, TN and OH Valley regions as the low-level jet
strengthens to 60+ kt and shifts northeast through moistening warm
sector. Vertical shear and overall character of wind profiles will
be more than adequate for organized severe storms, with potential
for LEWP, bowing segments and a few embedded supercells capable of
damaging wind and a few tornadoes. An upgrade to higher
probabilities might be needed in later outlooks once uncertainties
regarding the thermodynamic environment have been mitigated.
 
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#19
From Memphis' AM AFD on Saturday:

With regards to a severe threat...models are showing a prefrontal
trough signal forming in eastern Arkansas by 00z Sunday as the
surface wave crosses Missouri. Another feather in the cap for the
potential for surface-based convection. A 70kt LLJ from the
southwest will form just out ahead of the trough leading to an
evening period of potentially backed surface winds and few low
level mesos and/or bowing segments. Limiting factors will be
lapse rates and instability amounts after sunset. Have placed
wording in this morning`s HWO about this severe threat.
 
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#22
An upgrade to an enhanced risk of severe weather will likely occur here if more instability is realized in the warm sector. Could even see some residual marginal threat for wind in the Carolinas at day 4. Should be fun to monitor.
 
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#27
Greg Forbes has the TORCON for East Arkansas and West Tennessee at a 5. There is plenty of potential not that much if any crapvection, and hints on the NAM that we might get some cloud breaks in the delta.
 
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#29
The shear looks fairly unidirectional and storm mode won't be discrete too long as is often the case in Feb. It's honestly just nice to get a couple legit severe weather threats under our belt before things get interesting and/or hairy later on in the latter parts of spring and summer when this Kelvin Wave reaches the EP and tries to flip the ENSO base state and this low frequency pattern away from a western us trough.
 

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