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March 18-19th Possible Severe Wx Outbreak

This obviously sits in the shadow of Wednesday's setup, but the SPC has also expanded the Slight Risk area to include most of OK and a large swath of TX (including DFW) for Tuesday:

1615876817403.png
 
And the AFD from FWD (it's a long one)...

000
FXUS64 KFWD 160614
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
114 AM CDT Tue Mar 16 2021

...New Short Term, Aviation...

.SHORT TERM... /NEW/
/Through Wednesday/

The short term forecast period will be rather eventful over the
course of the next 36 hours. Forecast concerns include the
potential for dense fog this morning, isolated warm advection
convection this afternoon, additional strong/severe convection
along a Pacific front early Wednesday morning, and gusty
winds/fire conditions Wednesday afternoon.

The main feature of interest for this forecast period is a deep
upper low presently situated over Las Vegas, NV. Rather than
staying in Vegas, this low will instead make an eastward beeline
towards the Texas Panhandle today, inducing strong surface
cyclogenesis while establishing a stout warm advection regime over
the Southern Plains. In fact, weak height falls already spreading
into Texas ahead of this feature are strengthening low-level
southerly flow, which will allow a warm frontal boundary (nicely
delineated by the 65F isodrosotherm) to climb northward through
our CWA over the next several hours. As dewpoints in the 60s
encounter temperatures in the upper 50s, areas of fog and low
stratus already present over Southeast Texas and the Hill Country
will expand northward. A Dense Fog Advisory may become necessary
roughly east of I-35 sometime this morning, but will wait until
there is better evidence of development prior to issuance.

Following the eventual dissipation of any fog after daytime
mixing ensues, some partial clearing of low clouds can be
expected by the afternoon. However, a deck of mid and high cloud
cover should filter insolation for most of the day. Southerly
winds and warm advection should still allow highs to reach near 80
degrees for most of the CWA. By mid or late afternoon, some warm
advection showers or isolated thunderstorms may attempt to
initiate mainly across our southeastern zones where capping will
weaken the most. However, absent of any localized strong ascent or
lifting mechanism, any convection may struggle to become deep or
sustain itself within only a modestly favorable environment.
Thunderstorms in this area would likely not be able to become
strong or severe unless the environment was to drastically change
from current expectations. Most of the forecast area is expected
to remain precip-free through the daytime period.

The window for any strong or severe convection will be overnight,
roughly from midnight to ~8am. By this time, the upper low will
be digging into West Texas, and a rapidly deepening surface low
will be pushing eastward through Oklahoma. Its attendant N-S
oriented Pacific front will be the main mechanism for convective
initiation around midnight as this boundary impinges on our
western CWA border. Initial convective development will be
strongly aided by steepening mid-level lapse rates (perhaps as
much as 9 C/km) associated with vigorous ascent from the dynamic
upper low. However, most guidance suggests that weak surface-based
capping will likely remain in place, so these storms would
predominantly pose a hail threat initially as they either move
into or develop immediately over our western/southwestern zones.

Further convective evolution remains a bit uncertain overnight,
but the general thinking is that the abundance of dry mid-level
air (and resultant strong cold pools) along with the fast-moving
Pacific front should result in convection growing upscale into
one or small segments while progressing eastward at a fast clip.
Convection should become elevated and cold-pool dominant behind
consolidating outflows or perhaps the "effective" Pacific front at
that stage. However, ample deep layer shear should still allow
elevated storms to acquire mid-level rotation and produce hail in
the presence of those previously mentioned steep lapse rates.
Wouldn`t be surprised to see an isolated severe or damaging gust
along any outflow or bowing segment even if this would occur
several miles ahead of any bonafide convection. CAM guidance that
typically handles outflow-dominated convection well (such as the
NSSL WRF and the TTU WRF) illustrates this scenario nicely in
their 00z runs. The tornado threat is expected to be substantially
lower given what should be some modest surface-based capping and
negatively buoyant air within the lowest 1-2 km, along with the
tendency for convection to quickly become elevated behind the
outflow/front. This system is expected to move at a quick enough
pace to preclude any hydrologic issues within the CWA.

All activity should be exiting the area to the east early
Wednesday morning as the Pacific front brings 30-degree dewpoints
into the area amid gusty westerly winds. The combination of low
RHs and what will likely be Wind Advisory caliber wind speeds
should result in elevated fire danger especially west of I-35 on
Wednesday afternoon. Modest cold advection will keep highs several
degrees cooler, mainly in the upper 60s and low 70s.

-Stalley
 
SPC


Meanwhile, storms are expected to spread across Georgia and into the
Carolinas ahead of the advancing cold front, along with some
pre-frontal cellular development within a zone of strong warm
advection east of the mountains. Given ample instability and a very
favorably sheared environment, relatively widespread and locally
substantial severe weather potential is indicated -- including risk
for a few strong tornadoes. Potential is expected to expand
northward toward/into southern Virginia with time as the front
retreats into the evening, before convection begins to end from west
to east as the cold front moves toward -- and eventually off -- the
Atlantic Coast.

..Goss.. 03/16/2021
 
Okay I’m done joking now .. this is starting to get extremely serious and I’m starting to get that feeling .. I am praying for all the families and loved ones of anyone in the path of these storms in the coming days this is scary stuff but I believe we have great forecasting capabilities to get the word out to people at a rapid pace and give them enough time to put themselves in the best opportunity to get through the storm.

let’s pray this busts big time
 
Is this going to be a qcsl with individual rouge storms ahead or what?
 
Zander98al said:
Is this going to be a qcsl with individual rouge storms ahead or what?
Click to expand...

From NWS Birmingham


Severe threat is unfortunately increasing for Wednesday afternoon
and Wednesday night. Two waves of severe weather likely. The first
wave will develop Wednesday afternoon, mainly due to diurnal
heating. All modes of severe weather possible with the higher
potential for discrete cells. Hail potential likely higher with the
first wave due stronger updrafts and better mid level lapse rates.
A QLCS will move out of Mississippi and into western Alabama
Wednesday evening. This wave will contain much higher 0-6km bulk
shear, low level helicity, STP and EHI values. This wave of
severe storms will likely have the higher potential for stronger
long track tornadoes. The QLCS will take its time tracking
eastward across central Alabama Wednesday night, and still could
be impacting the far eastern counties by sunrise Thursday.
 
Wow, a level 3 risk already out for Thursday. I just hope there is something to screw things up like when we have winter storm threats and it isn't as bad as the models show.
 
Jrips2710 said:
From NWS Birmingham


Severe threat is unfortunately increasing for Wednesday afternoon
and Wednesday night. Two waves of severe weather likely. The first
wave will develop Wednesday afternoon, mainly due to diurnal
heating. All modes of severe weather possible with the higher
potential for discrete cells. Hail potential likely higher with the
first wave due stronger updrafts and better mid level lapse rates.
A QLCS will move out of Mississippi and into western Alabama
Wednesday evening. This wave will contain much higher 0-6km bulk
shear, low level helicity, STP and EHI values. This wave of
severe storms will likely have the higher potential for stronger
long track tornadoes. The QLCS will take its time tracking
eastward across central Alabama Wednesday night, and still could
be impacting the far eastern counties by sunrise Thursday.
Click to expand...

Damn, if that QLCS is still in eastern AL morning that going to cause some major issues in the Carolina’s later on Thursday afternoon.


Sent from my iPhone using Tapatalk
 
Not gonna lie, last nights WRFs and this mornings 3km NAM are giving me pause. WRFs keep the wind fields disjointed from the best instability in the day and then veers unidirectional aloft with the QLCS. The NAM is much better wind field wise, but still is very messy with convection, but we toss because it is 99% stupid.

Will be interesting to see what they do in later runs.
 
I will be in Wilmington Thursday...a much better spot for severe storms (generally) than Kernersville. Will see what happens.
 
Sleet City USA said:
Long range 3k and HRRR averaged soundings for AL mod/enh area
View attachment 79103View attachment 79104
Click to expand...
NAM has the more ominous wind profile for hail (given long straight mid and upper level Hodograph) and tornadoes given the backed flow towards the surface, but the HRRR is more impressive wrt thermodynamics/low level instability and low level lapse rates (less stability in the low levels like the NAM)
 
Poimen said:
I will be in Wilmington Thursday...a much better spot for severe storms (generally) than Kernersville. Will see what happens.
Click to expand...
My local met stopped just short of saying a tornado outbreak will happen.
He said golf ball or ping pong size hail is very possible with numerous storms rotating. We are at a level 4/5 for here.
Very scary stuff.
 
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Sleet City USA said:
SPC is definitely way more bullish than GSP on warm sector/cellular development
Click to expand...
GSP
The GFS is more progressive with the cold front and the severe
weather environment would not be able to fully solidify in that
case as the GFS has a full fropa between 18z Thurs - 00z Fri. This
would likely keep any severe weather east of the I-77 Corridor,
but the NAM and ECMWF suggest a slower progression of the system
and allows for diurnal heating and maximized instability to
become more established ahead of the cold front. In this case,
organized severe weather would likely move across the area and would
produce damaging winds, large hail, and possibly a short-lived
tornado. Due to the time discrepancies still in place with the
latest model trends, uncertainty in the severity of this event
still exists. PWAT values ~1-1.25" and the convective nature of
this event, localized flooding will possibly become an additional
threat, especially in the stronger storms and SW facing slopes in
the mountains.
Click to expand...
SPC
Meanwhile, storms are expected to spread across Georgia and into the
Carolinas ahead of the advancing cold front, along with some
pre-frontal cellular development within a zone of strong warm
advection east of the mountains. Given ample instability and a very
favorably sheared environment, relatively widespread and locally
substantial severe weather potential is indicated -- including risk
for a few strong tornadoes.
Click to expand...
 
WSFA12 out of Montgomery seems pretty bullish on pre-frontal development. Their in-house model shows this
FIOSTH5RGFGY7IHS76QIZGGAIA.png
 
Myfrotho704_ said:
Honestly I’m more concerned about the stuff in the evening/night as the LLJ picks up, HRRR shows supercells out in front of the QLCS close the the best 850mb LLJ and then turns it into a line with supercells in it View attachment 79115View attachment 79116View attachment 79117
Click to expand...

Looking at wind fields in the HRRR, it makes me think of the Centerpoint F3 and the Fultondale F3. It may be one of those events that go quiet for an hour due to messy storm mode to a cell becoming semi-discrete and going nuts for a brief period, before back to quiet again.
 
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