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

[TheProfessor]

Haven't been able to do an analysis on the mesoscale models yet, but perhaps I'll do one tonight when the WRF models show most of the event.

Anyways this is my early idea of what a potential day 1 risk may look like. It leans heavily on the 15z SREF, though my moderate risk isn't too different than the current one but extends to the west and north a bit.

[cycloneye]

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Sat Apr 11 2020

Valid 121200Z - 131200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR
CENTRAL/NORTHERN LOUISIANA...SOUTHEAST ARKANSAS...MUCH OF
MISSISSIPPI...WESTERN/CENTRAL ALABAMA......

...SUMMARY...
An outbreak of severe thunderstorms appears likely Sunday into
Sunday night, with the greatest threat expected from Louisiana
through much of the Southeast and Tennessee Valley. Strong
tornadoes, potentially widespread damaging winds, and large hail are
all possible.

...Synopsis...
The ejecting shortwave trough initially over the southern High
Plains on Sunday morning is forecast to move quickly eastward to the
lower MS Valley by early evening, and then accelerate northeastward
toward the Ohio Valley late Sunday night into Monday morning, as it
becomes absorbed within an amplifying longwave trough that will
encompass nearly all the CONUS by 12Z Monday. In conjunction with
the ejecting trough, a broad surface low centered over the
central/southern Plains on Sunday morning will move eastward to the
mid-MS Valley by 00Z Monday, and then move northeastward and rapidly
intensify into an intense cyclone over the lower Great Lakes by 12Z
Monday. A warm front will surge northward ahead of the low across
the lower MS Valley and Southeast, while a strong cold front will
move southward through much of the Plains in the wake of the
departing cyclone.

...East TX northeastward through much of the Southeast and TN
Valley...
One or more clusters of deep convection will likely be ongoing at
12Z Sunday morning somewhere over east TX and potentially into
portions of the lower MS Valley. The intensity and areal extent of
any such clusters remain uncertain, but ample shear and instability
will favor a threat of hail and damaging wind with any organized
convection at the start of the period. Some tornado threat will also
be present Sunday morning with any semi-discrete storms that begin
to interact with the richer low-level moisture in the vicinity of
the warm front. As this convection spreads northeastward,
intensification is possible into portions of the ArkLAMiss region,
with an increasing tornado threat in late morning/early afternoon
with any surface-based storms, given rapidly increasing low-level
moisture and shear. North of the warm front, evolution into a QLCS
will be possible, with a corresponding risk of damaging wind into
portions of the TN Valley.

Meanwhile, further south, moderate to locally strong instability is
forecast to develop along/south of the warm frontal position, which
will be modulated by the impact of outflow from any early convection
described above. Midlevel flow will increase to 70-100 kt as a
south-southwesterly low-level jet intensifies into the 40-60 kt
range. These wind profiles combined with ample instability (MLCAPE
of 1500-3000 J/kg) will support the potential for intense
supercells. Any surface-based initiation along and east of a
pseudo-dryline moving into western LA by late afternoon could evolve
into one or more long-tracked supercells capable of producing strong
tornadoes, large hail, and damaging wind gusts. The extent of
development within the warm sector remains somewhat uncertain, given
the presence of a capping inversion and generally subtle foci for
initiation.

While the conditional risk of all severe hazards will be quite high
if supercells develop, uncertainty remains regarding how convection
will evolve from the morning into the afternoon. Any remnant outflow
related to early convection will determine the northern extent of
the higher-end tornado potential, and some guidance suggests the
potential for elevated convection within a midlevel moist plume
across the warm sector during the afternoon, which could either
dampen the severe potential, or evolve into surface-based convection
with a substantial severe threat. Given these factors, there is too
much uncertainty to upgrade the ongoing outlook at this time.

Evolution into more of QLCS is suggested by most guidance by Sunday
evening, which would pose an increasing threat of widespread
damaging winds and a few tornadoes across much of AL into
western/central GA through the overnight hours. Higher wind
probabilities may be needed in subsequent outlooks if confidence in
this scenario grows.

...Central/southern Plains into the Ozark Plateau...
While widespread convection to the southeast will likely limit
transport of deeper Gulf moisture into the Plains/Ozarks, more
modest moisture that was advected into the region on Saturday should
remain in place ahead the advancing surface low and cold front
Sunday afternoon. Steep lapse rates and cold midlevel temperatures
associated with the primary shortwave will support moderate
destabilization. Wind profiles will likely not favor classic
supercells, with some backing of mid/upper-level flow expected, but
effective shear will be supportive of organized structures. Large
hail (potentially significant) will be the primary threat, with some
wind potential if any upscale growth occurs. Wind profiles will not
generally favor tornado potential, though robust updrafts
interacting with locally enhanced vorticity near the surface cyclone
could produce a tornado or two.

...TN Valley into the OH Valley -- Sunday night...
Substantial uncertainty remains regarding the potential for
destabilization from northern portions of the TN Valley into the OH
Valley, due to the potential for widespread convection to the south
of this area. However, rapidly strengthening wind fields in advance
of the deepening cyclone will support the potential for damaging
wind and perhaps a tornado risk by Sunday evening should even modest
destabilization occur, as strong convection attempts to move in from
the southwest in tandem with the deepening cyclone.

... Eastern Georgia into the Carolinas/Mid Atlantic...
Substantial low-level moistening is expected over eastern GA into
the Carolinas/Mid Atlantic through the period. There is a nonzero
risk of organized convection along/north of the warm front during
the day into the evening, which would pose some risk of locally
damaging wind or perhaps a tornado, but confidence in this scenario
is low at this time. A more likely scenario is for widespread
upstream convection to evolve into multiple clusters or a QLCS and
move into this region sometime early Monday morning. Intense wind
profiles will support a risk of widespread damaging wind and a few
tornadoes, given sufficient instability.

The magnitude and coverage of the severe threat in this region will
be determined in part by how fast organized convection approaches
from the west. If convection accelerates and arrives faster that
current guidance would indicate, then there is less time for
low-level moistening and destabilization, and the magnitude and
northward-extent of the threat may be limited. If convection does
not arrive until very late in the period, then a more substantial
severe threat could evolve. If some of the slower guidance turns out
to be accurate, then the primary severe threat in this region may
not come until the D3/Monday period. Probabilities may need to be
increased in this area once the details come into better focus.

..Dean/Broyles.. 04/11/2020

[TheProfessor]

SPC keeping it a moderate risk, but they introduced a 45% wind threat for parts of Mississippi, Alabama, Tennessee, and extreme eastern Arkansas.

[Shell Mound]

Over the past two runs, the ECMWF has trended toward a shallower trough, weaker wind fields, narrower hodographs, and a less pronounced EML over the warm sector. The threat for a significant tornado outbreak with discrete cells seems to have decreased substantially. A mixed mode with a strong QLCS spin-up or two seems more probable, along with widespread damaging winds, but nothing remotely close to what some people were suggesting, at least as far as strong (or violent) tornadoes are concerned. This is very good news.

[TheProfessor]

Over the past two runs, the ECMWF has trended toward a shallower trough, weaker wind fields, narrower hodographs, and a less pronounced EML over the warm sector. The threat for a significant tornado outbreak with discrete cells seems to have decreased substantially. A mixed mode with a strong QLCS spin-up or two seems more probable, along with widespread damaging winds, but nothing remotely close to what some people were suggesting, at least as far as strong (or violent) tornadoes are concerned. This is very good news.

When you look at a collection of models the high end parameters are still there. What this system does have is a few legit failure modes that can cap it's potential. One of which are storms not rooting into the boundary layer, another one is messy storm mode and more convection. I think these will be the reason for a busted forecast, not the parameters lining up right now.

[cycloneye]

 https://twitter.com/wxtrackercody/status/1249153508332404740

[TheProfessor]

https://twitter.com/wxtrackercody/status/1249153508332404740

UH(Or lack there of) has been the talk of today. Here's a good thread about perhaps not following it so strictly.

https://twitter.com/evan_bentley/status ... 9409092611

It will be interesting to see if storms have trouble gaining footing in the boundary layer though, it's a legit failure mode. But it does seem suspicious that some of these HRRR storms are producing UH, but they're surviving for long periods. The 0z HRRR also has some hefty storms later in the evening for southern Louisiana and into southern Mississippi and central and southern Alabama, though this looks semi-discrete at best and eventually evolves into a QLCS, even a QLCS could develop strong tornadoes in this atmosphere. Most of this is happening in the enhanced risk area as well so a strong QLCS could verify that risk if it were to occur.

[cycloneye]

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0752 AM CDT Sun Apr 12 2020

Valid 121300Z - 131200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS TODAY INTO
TONIGHT FROM THE ARK-LA-MISS EASTWARD INTO AL AND WESTERN GA...

...SUMMARY...
An outbreak of severe thunderstorms is likely today into tonight,
with the greatest threat expected from Mississippi across Alabama
into western Georgia. Strong tornadoes, widespread damaging winds,
and large hail are all possible.

...Synopsis...
A complex forecast today with multiple scenarios possible across a
broad area from the lower MS Valley into the TN/OH Valleys and the
Southeast. A midlevel trough near the TX Big Bend this morning will
accelerate east-northeastward to the Ark-La-Miss by this evening and
the Appalachians by the end of the period, in response to continued
amplification of a large-scale trough over the north central CONUS.
At the surface, a cyclone will move across OK today and develop
eastward to AR by this evening, followed by substantial deepening as
the cyclone moves northeastward to the OH Valley/Great Lakes
overnight. A moist/unstable warm sector will surge northward across
LA/MS/AL/GA today, setting the stage for severe storms with the
ejecting shortwave trough and deepening cyclone through tonight.
Several scenarios are possible within the overall outlook area, with
substantial uncertainty related to early/ongoing convection now in
TX.

...Northeast TX to northern MS/AL and TN this afternoon...
An ongoing cluster of severe storms continues to move
east-northeastward into east central and northeast TX this morning,
in association with a lead shortwave trough. All hazards will be
possible with this cluster which will include a mixed convective
mode of supercells and bowing segments. Low-level moisture will
surge northward today across LA/MS/AL in response to the deepening
cyclone moving from OK to AR. The main question through mid
afternoon will be whether or not surface destabilization will keep
pace with the initial cluster. If warming/moistening can occur
quickly enough, the chance for surface-based storms on the southern
flank will increase. This may occur coincident with an environment
characterized by moderate buoyancy (MLCAPE of 1500-2500 J/kg), very
strong low-level shear (0-1 km SRH of 400-500 m2/s2) as the
low-level jet strengthens over LA/MS, and effective bulk shear in
excess of 70 kt. This environment will favor embedded supercells
capable of producing strong tornadoes and damaging winds. Again,
the main questions in this corridor through this afternoon will be
the degree of organization of the late morning-early afternoon
convection, and its phasing with the surface warm front.

...MS/AL/GA/Carolinas late this afternoon through tonight...
To the south of the initial storm cluster crossing northern
MS/AL/TN, a separate pre-frontal band of convection is expected to
develop by late afternoon from southern MS into western/central AL.
This convection will be well east the synoptic cold front, in an
environment with surface-based buoyancy and very strong vertical
shear. A broken band with embedded supercells appears likely to
persist well into the overnight hours, with an associated threat for
strong tornadoes and damaging winds. The pre-frontal convection
should reach the western Carolinas by 09-12z.

...Red River Valley this afternoon to the OH Valley overnight...
An arc of convection will likely form this afternoon near the
surface low in southeast OK, and within the left-exit region of the
mid-upper jet. This convection will subsequently spread eastward
and northeastward into AR through late afternoon/evening. The
northward extent of destabilization in AR/western TN this
afternoon/evening will depend largely on the intensity and extent of
the early afternoon convection moving from LA into northern MS.
Still, steep midlevel lapse rates with the ejecting midlevel wave
and strong deep-layer vertical shear will favor fast-moving
supercells and line segments capable of producing large hail and
damaging winds. Similar to AR this afternoon, the northeast extent
of the damaging wind and tornado threat into tonight will depend
largely on how widespread/organized the convection is across
northern MS/AL this afternoon/evening, and the degree of low-level
recovery in the wake of that convection.

..Thompson.. 04/12/2020

[newtotex]

What’s the timing for the warm front moving north? Here in Birmingham it doesn’t feel like “tornado weather.”

[TheProfessor]

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 106
NWS Storm Prediction Center Norman OK
1040 AM CDT Sun Apr 12 2020

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of
Far southeast Arkansas
Northeast Louisiana
Northern and central Mississippi

* Effective this Sunday morning and evening from 1040 AM until
800 PM CDT.

...THIS IS A PARTICULARLY DANGEROUS SITUATION...

* Primary threats include...
Several tornadoes and a few intense tornadoes likely
Widespread damaging winds likely with isolated significant gusts
to 80 mph possible
Scattered large hail and isolated very large hail events to 2
inches in diameter possible

SUMMARY...Intense bowing line with a history of several tornadoes in
northwest Louisiana will progress rapidly east-northeast this
afternoon. Additional semi-discrete suprecells may develop ahead of
the line as well across parts of northern and central Mississippi.
Environment is supportive of several tornadoes, some of which will
likely be strong in addition to potential widespread damaging winds.

The tornado watch area is approximately along and 85 statute miles
north and south of a line from 5 miles north northwest of Monroe LA
to 20 miles south of Columbus MS. For a complete depiction of the
watch see the associated watch outline update (WOUS64 KWNS WOU6).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Tornado Watch means conditions are favorable for
tornadoes and severe thunderstorms in and close to the watch
area. Persons in these areas should be on the lookout for
threatening weather conditions and listen for later statements
and possible warnings.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 105...

AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 2 inches. Extreme turbulence and surface wind
gusts to 70 knots. A few cumulonimbi with maximum tops to 550. Mean
storm motion vector 25045.

...Grams

[cycloneye]

The latest.

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sun Apr 12 2020

Valid 121630Z - 131200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS NORTHEAST
LA...SOUTHEAST AR...MS...AL...WESTERN GA...SOUTHERN MIDDLE TN...

...SUMMARY...
An outbreak of severe thunderstorms is likely through tonight, with
the greatest threat expected from northeast Louisiana, Mississippi,
Alabama, southern Middle Tennessee and western Georgia. Strong
tornadoes, widespread damaging winds, and large hail are all
possible.

...Synopsis...
A complex forecast with multiple scenarios possible across a
broad area from the Lower MS Valley into the TN/OH Valleys and the
Southeast. A compact shortwave trough over the Edwards Plateau of TX
will accelerate east-northeast into the Ark-La-Miss by this evening
and towards eastern KY/TN by the end of the period, in response to
continued amplification of a large-scale trough over the
north-central states.

...Northwest LA to northern AL/middle TN...
An ongoing MCS with a history of several confirmed but brief TDSs
earlier this morning will continue to move east-northeast along an
intensifying baroclinic zone across parts of northern/central MS
into northern AL/middle TN. Tornadoes and damaging winds will be
likely with this MCS which will include a mixed convective mode of
bowing segments and potential supercells developing just ahead of
the cluster on its southern flank.

The presence of upper 60s to low 70s surface dew points in much of
LA and southern MS will spread north and likely reach northern MS to
western AL between 21-00Z. This should overlap strong low-level
shear (0-1 km SRH of 400+ m2/s2) as the low-level jet strengthens
and shifts northeast. The environment will favor embedded supercells
capable of producing strong tornadoes and damaging winds, the most
substantial of which may occur from northeast LA through
north-central MS into northern AL and southern middle TN. There is
still enough uncertainty with regard to convection outpacing
stronger surface-based instability (especially with northeast
extent), as well as the overall convective mode, to preclude an
upgrade to High Risk.

...Southern MS to GA/Carolinas...
To the south of the initial MCS crossing northern MS/AL into TN, a
separate pre-frontal band of convection is expected to become
sustained by early evening from southern MS into central AL. This
convection will be well east of the synoptic cold front, in an
environment with moderate surface-based buoyancy and very strong
vertical shear. A broken band of embedded supercells appears likely
to develop through the evening and overnight, with an associated
threat for strong tornadoes and damaging winds. The pre-frontal
convection should reach the western Carolinas by 09-12z.

...Lower Red River Valley to the OH Valley...
An arc of convection will likely form later this afternoon just
ahead of the compact shortwave trough and associated surface cyclone
in eastern OK to northeast TX, within the left-exit region of the
mid-upper jet. This convection will subsequently spread east then
northeast across the Mid-South during the late afternoon/evening.
The northward extent of destabilization in AR/western TN this
afternoon/evening will depend largely on the intensity and extent of
the early-day MCS moving from LA into northern MS.

Still, steep midlevel lapse rates with the ejecting mid-level wave
and strong deep-layer vertical shear will favor fast-moving
supercells and line segments capable of producing large hail and
damaging winds. The northeast extent of the damaging wind and
tornado threat into tonight will depend largely on how
widespread/organized the convection is across northern MS/AL this
afternoon/evening, and the degree of low-level recovery in the wake
of that convection.

..Grams/Bentley.. 04/12/2020

[cycloneye]

Tornado watch for parts of LA and Miss.

 https://twitter.com/NWStornado/status/1249402848456015872

[cycloneye]

 https://twitter.com/wxtrackercody/status/1249418463346597890

[Bunkertor]

17 minutes 20z outlook delay

[Bunkertor]

686
WFUS54 KJAN 122128 RRA
TORJAN
MSC061-067-122230-
/O.NEW.KJAN.TO.W.0035.200412T2128Z-200412T2230Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE JACKSON MS
428 PM CDT SUN APR 12 2020

..TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA

THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHEASTERN JASPER COUNTY IN EAST CENTRAL MISSISSIPPI...
JONES COUNTY IN SOUTHEASTERN MISSISSIPPI...

* UNTIL 530 PM CDT.

* AT 428 PM CDT, A CONFIRMED LARGE AND DESTRUCTIVE TORNADO WAS
OBSERVED NEAR COLLINS, MOVING NORTHEAST AT 50 MPH.

TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA.
THIS IS A PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW!

HAZARD...DEADLY TORNADO.

SOURCE...RADAR CONFIRMED TORNADO.

IMPACT...YOU ARE IN A LIFE-THREATENING SITUATION. FLYING DEBRIS
MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE
HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO HOMES,
BUSINESSES, AND VEHICLES IS LIKELY AND COMPLETE
DESTRUCTION IS POSSIBLE.

* THE TORNADO WILL BE NEAR...
HEBRON AROUND 445 PM CDT.
MOSS AROUND 500 PM CDT.
SANDERSVILLE AROUND 510 PM CDT.
HEIDELBERG AROUND 515 PM CDT.
STAFFORD SPRINGS AROUND 520 PM CDT.

OTHER LOCATIONS IMPACTED BY THIS TORNADIC THUNDERSTORM INCLUDE SOSO.

[Bunkertor]

605
WFUS54 KJAN 122206 RRA
TORJAN
MSC023-061-122300-
/O.NEW.KJAN.TO.W.0038.200412T2206Z-200412T2300Z/

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE JACKSON MS
506 PM CDT SUN APR 12 2020

..TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA

THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHEASTERN JASPER COUNTY IN EAST CENTRAL MISSISSIPPI...
CLARKE COUNTY IN EAST CENTRAL MISSISSIPPI...

* UNTIL 600 PM CDT.

* AT 506 PM CDT, A CONFIRMED LARGE AND DESTRUCTIVE TORNADO WAS
OBSERVED NEAR HEIDELBERG, OR 10 MILES EAST OF STRINGER, MOVING
NORTHEAST AT 55 MPH.

TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA. THIS IS A
PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW!

HAZARD...DEADLY TORNADO.

SOURCE...WEATHER SPOTTERS CONFIRMED TORNADO.

IMPACT...YOU ARE IN A LIFE-THREATENING SITUATION. FLYING DEBRIS
MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE
HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO HOMES,
BUSINESSES, AND VEHICLES IS LIKELY AND COMPLETE
DESTRUCTION IS POSSIBLE.

* THE TORNADO WILL BE NEAR...
VERNON AROUND 510 PM CDT.
PAULDING AROUND 515 PM CDT.
BARNETT AND GOODWATER AROUND 520 PM CDT.
ORANGE AROUND 525 PM CDT.
QUITMAN AND STONEWALL AROUND 535 PM CDT.
MIDDLETON, SABLE AND SYKES AROUND 545 PM CDT.
SNELL AROUND 555 PM CDT.

OTHER LOCATIONS IMPACTED BY THIS TORNADIC THUNDERSTORM INCLUDE
PACHUTA.

[Bunkertor]

Damage in Laurel. MS
https://twitter.com/DualDoppler/status/ ... 84/photo/1

[northjaxpro]

They are already stating this tornado in progress on the ground in Southern Mississippi is at least an EF-4 or possible EF-5.

[HurricaneBelle]

They are already stating this tornado in progress on the ground in Southern Mississippi is a at least an EF-4 or possible EF-5.

yeah I'll buy that

 https://twitter.com/ConnorWX/status/1249456589712633858

[cycloneye]

Extensive damage in Soso but hopefully no fatalities.

 https://twitter.com/rzweather/status/1249493237053652993