Severe WX Severe Weather Threat - November 30th-December 2nd, 2023

[Taylor Campbell]

Discussion:
ACUS03 KWNS 280826
SWODY3
SPC AC 280825

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0225 AM CST Tue Nov 28 2023

Valid 301200Z - 011200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
SOUTHEAST TEXAS AND INTO FAR WESTERN LOUISIANA...

...SUMMARY...
Scattered storms, some severe, will be possible during the day on
Thursday, mainly over southeast Texas.

...Synopsis and Discussion...
A shortwave trough will move quickly east across NM and into
northwest TX on Thursday, then eject northeastward across OK and
into MO overnight. Modest height falls are forecast across much of
the southern Plains during the day, but rapid warming aloft will
occur over southern parts of TX and LA by mid afternoon as the upper
wave ejects.

A relatively early risk of severe storms, including a few tornadoes,
appears possible mainly from late morning through mid afternoon
across southeast TX, while temperatures aloft remain cool and
midlevel lapse rates are maximized. A plume of upper 60s F to near
70 F dewpoints will spread inland, with MLCAPE through midday of
around 1500 J/kg. Given the warm advection regime and antecedent
cooler air mass with high pressure to the east, substantial
southerly flow including 50+ kt at 850 mb is forecast, which will
enhance shear. Effective SRH looks to be maximized from midday to
early afternoon, with values over 300 m2/s2.

There appears to be at least a few hours of overlap between the more
favorable instability and stronger shear, and during this time,
supercells including a couple tornadoes could occur. Early day
storms could be substantial and affect air mass quality. However,
this event will be driven mainly by moisture advection and isolated
severe cells within any larger scale convective area will still have
severe potential, including brief tornadoes.

..Jewell.. 11/28/2023

$$

 

[KevinH]

We’ll see what happens

 

[JPWX]

NWS Memphis afternoon discussion: "As the system occludes, the
warm sector should be pinched off well to the south. As a result,
despite strong shear, the severe threat is very low attm. If the
general track of the system keeps moving north then the warm sector
could eventually come into play across parts of north MS. Not likely
but will keep on eye on this. This system is moving quite quickly
with the best dynamics and lift pushing east by 12z Friday."

 

[JPWX]

I don't know what NWS Memphis is seeing, but all the Global models are showing a neutral to slightly negative tilted trough swinging thru Friday.

 

[KevinH]

NWS Memphis afternoon discussion: "As the system occludes, the
warm sector should be pinched off well to the south. As a result,
despite strong shear, the severe threat is very low attm. If the
general track of the system keeps moving north then the warm sector
could eventually come into play across parts of north MS. Not likely
but will keep on eye on this. This system is moving quite quickly
with the best dynamics and lift pushing east by 12z Friday."

Yeah I haven’t heard a lot of buzz about this system (yet) but we ARE talking about Dixie here and she COULD end up giving all of us the middle finger at the last minute without warning sooooooo…

 

[CheeselandSkies]

NWS Memphis afternoon discussion: "As the system occludes, the
warm sector should be pinched off well to the south. As a result,
despite strong shear, the severe threat is very low attm. If the
general track of the system keeps moving north then the warm sector
could eventually come into play across parts of north MS. Not likely
but will keep on eye on this. This system is moving quite quickly
with the best dynamics and lift pushing east by 12z Friday."

Memphis' CWA isn't expected to be in the threatened area with this, hence this AFD. The risk area is southeast Texas/far western LA.

 

[Tennie]

SPC issued a Day 2 ENH. with 10% chance for tornadoes (though no hatched area yet):



And here's the discussion:

SPC AC 290654

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1254 AM CST Wed Nov 29 2023

Valid 301200Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A SMALL
PART OF SOUTHEAST TEXAS...

...SUMMARY...
Scattered storms, some severe, will be possible during the day on
Thursday, mainly over southeast Texas. A couple tornadoes will be
possible during the day. Otherwise, marginal hail will be possible
extending northward into parts of Oklahoma.

...Synopsis...
An upper trough will move across the southern Plains on Thursday,
with the primary speed max moving from southwest TX toward the Red
River through evening, and across the mid MS Valley by 12Z Friday.
Relatively cool midlevel temperatures will exist over the southern
Plains early in the day, but rapid warming aloft is forecast over
the southern half of TX and into LA to the south of the jet core.

Low pressure will develop over northwest TX into OK by late
afternoon, near the track of the upper wave. Low-level lapse rates
will steepen in the veering flow over western TX, but the eastward
extent of boundary-layer mixing will be impeded by the moistening
air mass to the east which will be a bit cool, and contain scattered
showers and thunderstorms. Still, a plume of upper 60s F dewpoints
will surge north across the middle TX Coast, with a warm front
traversing southeast TX and then southwest LA overnight. Aiding
moisture advection and shear will be a 50+ kt low-level jet.

...Much of southeast TX into southwest LA...
A conditional setup for supercells and a few tornadoes is forecast
on Thursday, as low-level moisture increases well ahead of the upper
wave, with a warm front pushing north through the period. Impressive
SRH values will exist near the warm front, and effective-layer SRH
of 300-400 m2/s2 will overlap the instability axis to the west.

The primary negative factors for a more substantial severe weather
event include the overall nebulous warm advection/forcing mechanism
and early-day storms, and warming temperatures aloft south of the
midlevel jet. The ability of storms to fully ingest the saturated
boundary-layer air mass and utilize the lower portions of the
hodograph is also in question. That said, there may be a focused
area where storms developing within the warm advection regime can
gain access to the instability plume and utilize the stronger shear.
Given the strength of the shear, have opted to introduce a 10%
tornado area for portions of southeast TX mainly from late morning
through mid afternoon.

Other storms may persist overnight into LA, with veering low-level
winds and overall weaker instability.

...North TX into OK...
Lapse rates will be steepest north of the speed max from northwest
TX into OK late in the afternoon and through evening. A prominent
midlevel dry slot will push across all of central TX and into
south-central OK by 00Z as deep-layer shear increases.

Scattered storms are expected during the afternoon over northern TX
and OK, in the low-level warm advection regime. Forecast soundings
show sufficient elevated instability to support hail in the stronger
cells.

..Jewell.. 11/29/2023

 

[TH2002]

From what I've seen, these sneaky TX setups ALWAYS either over or under perform (at least as far as the tornado threat is concerned) with litterally no in between. All we can do is play the usual waiting game...

 

[UncleJuJu98]

From what I've seen, these sneaky TX setups ALWAYS either over or under perform (at least as far as the tornado threat is concerned) with litterally no in between. All we can do is play the usual waiting game...

Yeah I'm staying out of trying to forecast this one lol. Once it's a threat west of Louisiana I don't have much observing experience. I stay within Dixie. Texas and the plains have a little bit different M.O.s when it comes to tornadoes and severe weather. Not a super big difference but still.

Lol I'll be of help sharing what trey posts and maybe some other guys.

 

[JBishopwx]

 

[TheSuckZone]

Outlook is skeptical

Forecast vertical shear profiles are impressive with large, curved
low-level hodographs becoming elongated/straight near 3 km. Strong
low-level southerly flow, with around 40-50 kt at 850 mb, is
expected. Effective SRH values greater than 300 m2/s2 near and north
of a warm front across east TX are depicted in forecast guidance as
well. This shear space conditionally would support supercell
thunderstorms.

However, low-level thermodynamics appear problematic. Surface
temperatures and dewpoints may struggle to reach higher than 68-69 F
(except perhaps near the immediate coast). Furthermore, cloudiness
and morning convection will limit heating, and forecast soundings
indicate low-level lapse rates remaining quite poor and nearly moist
adiabatic. HREF members also continue to depict stronger negative UH
tracks than positive UH tracks, which is an indication that storms
may struggle to be rooted near the surface, limiting access to
better low-level vertical shear. Additionally, forecast guidance
shows modest warming through the day in the 850-500 mb layer, while
stronger large-scale ascent remains focused north of the region.

An outlook downgrade was considered.

 

[Austin Dawg]

The forecast here in Austin is we have a tornado that that is low, but it’s stronger towards Houston and Eastern Texas. This is the classic storm formation you usually get in February so watch it closely. Still isn’t February but the temperatures moved from the high 40’s this morning to low 60's today. Dews are rising.

 

[Austin Dawg]

My laptop is being repaired and I am trying to figure out how to use the iPad.

 

[JBishopwx]

..THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST TEXAS...

...SUMMARY...
Scattered storms with some severe, will be possible today over
southeast Texas. A few tornadoes are expected, along with hail and
isolated damaging wind gusts. Further north, into parts of east
Texas and southern Oklahoma, hail along with a few strong wind gusts
will also be possible.

...Southern Plains/Lower Mississippi Valley...
A mid-level trough will move across the Desert Southwest and
northern Mexico today. An associated 70 to 85 knot mid-level jet
will move eastward across northern Mexico and into west Texas by
this afternoon. Ahead of the mid-level jet, moisture advection will
occur across the Texas Coastal Plain. Surface dewpoints are forecast
to increase into the 65 to 70 F range from the middle Texas Coast
northward into the area west of the Houston Metro. As surface
heating takes place along and near the moist axis, MLCAPE is
forecast to increase into the 1200 to 1500 J/kg range. As the system
approaches, a 50 to 60 knot low-level jet will be maintained across
east Texas. Lift associated with the low-level jet will aid
convective development during the day over much of east Texas
extending northward into the Ark-La-Tex. A marginal severe threat
will be possible across much of this weakly unstable airmass
throughout the day.

Further south from the middle Texas Coast into Southeast Texas, the
environment will become favorable for supercells by around midday.
As surface dewpoints and low-level shear increase, Significant
Tornado Parameter is forecast to peak in the 4 to 5 range by early
to mid afternoon. RAP forecast soundings just west of Houston at 21Z
have 0-3 km storm-relative helicity reaching about 325 m2/s2. This
will likely support a tornado threat associated with supercells that
form and move into the Houston area this afternoon. A small cluster
of tornadoes is expected across southeast Texas. Although damaging
wind gusts will also be possible, this threat will be associated
with supercell downdrafts and should remain isolated. There could
also be a localized large hail threat with supercells. The potential
for severe storms could continue into the evening as a convective
cluster moves from southeast Texas into southwest Louisiana.

 

[JPWX]

A great day for the radar in Houston to be down for maintenance.

 

[KevinH]

A great day for the radar in Houston to be down for maintenance.

Seems to work every time SMH

 

[JBishopwx]

From Trey:

 

[JBishopwx]

Enhanced drop.

 

[TH2002]

When was the last time the SPC downgraded an outlook prior to the event actually starting?

 

[tennessee storm chaser]

When was the last time the SPC downgraded an outlook prior to the event actually starting?

I was not impressed with the system from the get go