375
FXUS64 KLUB 012254
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
554 PM CDT Wed May 1 2024

...New MESOSCALE UPDATE...

.MESOSCALE UPDATE FOR ONGOING SEVERE STORMS...
Issued at 554 PM CDT Wed May 1 2024

Semi-discrete supercells are ongoing across the extreme southeastern
TX PH while additional convection continues to unzip along the
dryline as it propagates westward. The field of horizontal
convective rolls has widened ahead of the semi-discrete supercells
amidst a favorable environment to maintain discrete propagation and
tornadic potential now through next 60-90 minutes. Cyclic behavior
has occurred with the supercell in Hall County, and deviant tornado
motion is expected. Incoming photos from social media have indicated
a wide base with evidence of occlusions, and the most recent photo
indicates a ragged wall cloud beneath a smooth, sculpted updraft
which reveals the depth of the upward-forced, stable air (i.e., the
LCL-LFC separation) and a brief tornado was recently reported with
the supercell in Hall County. Large, vertical accelerations will
continue to offset the relatively weaker deep-layer shear, with
recent mesoscale analysis indicating SBCAPE values in excess of
4,000 J/kg. These estimates appear accurate based off of recent West
Texas Mesonet observations of dewpoints in the lower 70s in addition
to modified temperatures now in the lower 80s within the inflow
region where southeasterly winds near 20-25 mph persist across the
extreme southeastern TX PH. Storm mergers will enhance tornadic
potential with an expectation for tornadoes to become rain-wrapped.
Deviant tornado movement will be accentuated by strong, internal
surges associated with rear-flank downdrafts and extreme rainfall
will accompany the RFD surges. Farther south along the HWY-87
corridor, a group of left-moving supercells continue to race
northward at around 40 mph and will pose a threat for very large
hail with an eventual focus towards wind-damage as cold pools merge
and cells evolve upscale into a Mesoscale Convective System (MCS).
The MCS will move eastward with downshear Corfidi vectors near 35 kt
(40 mph) the threat for severe weather remaining intact for the rest
of the Rolling Plains heading into the evening.

Sincavage

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 127 PM CDT Wed May 1 2024

A shortwave impulse was analyzed on water vapor imagery this early
afternoon over northeastern Mexico and was propagating into far
southwestern Texas. Meanwhile, shortwave troughing well to the north
of the CWA is beginning to emerge over the west-central Great
Plains. The former impulse will serve as the impetus for the
initiation of thunderstorms across the Caprock and Rolling Plains
within the next few hours. At the surface, West Texas Mesonet (WTM)
and METAR data have been detecting steady pressure falls, as
indicated in the prior discussions, at around 1 mb/1 hr as the lee
cyclone located in the OK/TX PH region gradually deepens. The
dryline continues to sharpen with a secondary lee cyclone analyzed
south of the I-40 corridor in far eastern New Mexico, and the
dryline was delineated along the I-27/HWY-87 corridors as per recent
WTM data. The moist sector is particularly buoyant with dewpoints
beginning to breach 70 degrees across a few WTM sites in the Rolling
Plains, and the billow field draped across the Rolling Plains
earlier has since dissipated as a deepening cu field advects
poleward from the Permian Basin. Congested cu was also evident on
visible satellite imagery across the extreme south-central TX PH,
with additional congested cu along the edge of the differential
heating boundary anchored across the extreme southwestern TX PH
where temperatures have risen into the middle 80s on the western
periphery of this boundary. This differential heating boundary has
also been reinforced by the now-remnant outflow, while a secondary,
westward-propagating outflow boundary was analyzed across the
southeastern Rolling Plains, though the airmass in its wake is not
overturned.

The 18Z RAOB from WFO MAF indicated a pristine elevated mixed layer
(EML), with 700-500 mb lapse rates of 8.5 deg C/km atop a weakening
cap (MLCINH now at -48 J/kg compared to -123 J/kg on the 12Z RAOB).
The arrival of the 700 mb trough was also sampled by the 18Z RAOB
from WFO MAF, with south-southwesterly flow near 20 kt that
continues to advect towards the CWA. Mixed-layer CAPE values were in
excess of 3,000 J/kg while most-unstable parcel trajectories yield
over 4,000 J/kg, and this reflects the estimates of RAP-derived CAPE
values on the SPC Mesoscale Analysis. Explosive thunderstorm
development is expected this afternoon across the Caprock and
Rolling Plains, with the potential for a bimodal convective
situation initially. Thunderstorms are expected to unzip northward
along the sharpening dryline as convective temperatures are reached
from intense, diabatic heating amidst strengthening low-level
convergence; and a more-isolated threat for supercells also exists
across the extreme southeastern TX PH where discrete propagation
will occur in the event storms remain cellular. Destructive
interference from rapid cellular development and the splitting of
cells along the HWY-87 and into the I-27 corridors will govern a
mixed-mode of embedded mesocyclones initially that will pose a
threat for significant (2"+) hail and wind-damage. Inverted-V
profiles, excessive hydrometeor loading; and large, upward-directed
accelerations from strong-extreme instability will directly result
in swaths of wind-damage. However, the dampened mid-level flow
should act to temper mesocyclones from remaining intact within the
broken line/MCS along the I-27/HWY-87 corridors as it propagates
eastward into the Rolling Plains. The amalgamation of cold pools and
intensity of the theta perturbations associated with downdrafts will
also pose a risk for wind-driven hail, with swaths of 60-70 mph
likely with isolated significant gusts to 75 mph possible heading
into the evening as the MCS matures.

The aforementioned area of congested cu across the extreme south-
central TX PH should serve as a focus for the initiation of one or
two cells that will rapidly become severe this afternoon. WTM data
continues to indicate a corridor of backed, southeasterly flow
between 15-25 mph with theta-e values approaching 360 K and upper
60/lower 70 dewpoints. This particular area and east-southeastward
into the rest of the extreme southeastern TX PH and northern Rolling
Plains is where the potential for tornadoes should be maximized as
initial coverage of storms remain isolated. Discrete, right-moving
propagation would foster a cyclic behavior to supercells with
deviant tornado movement expected as low-level storm-relative inflow
intensifies as a function of the isallobaric response from the
deepening cyclone in the OK/TX PH. The dampened storm-relative flow
at anvil-level, and overall weaker flow throughout the mid-levels as
the CWA remains beneath the left-exit region to the 250 mb jet
streak, will also result in HP supercells with large and buoyant
rear-flank downdrafts that would also result in a potential for
localized wind-damage. The depth of the effective inflow-layer
should also facilitate a favorable injection region of hydrometeors,
with the potential for very large hail and/or swaths of accumulating
hail possible. Flash flooding will accompany the slow-moving
supercells from extreme rain rates owing to the excessive water
loading.

Eventual upscale growth is expected area-wide towards dusk with an
MCS propagating eastward across the Rolling Plains. The primary
hazards near and after dusk should focus towards wind-damage and
flash flooding, with the MCS clearing the eastern zones after
midnight tonight. Benign weather is expected the rest of the night
with southerly flow remaining intact ahead of a southward-moving
cold front that will move through the CWA tomorrow morning. Cooler,
though still warm, temperatures will follow as northerly winds
persist ahead of renewed chances for thunderstorms return to the far
eastern Rolling Plains tomorrow evening.

Sincavage

&&

.LONG TERM...
(Thursday night through next Tuesday)
Issued at 127 PM CDT Wed May 1 2024

By late Thursday afternoon, a cold front will still be slowly
dipping to the south across the area with a dry line extending to
the south out of the Rolling Plains/Big Bend area. There still
exists model uncertainty on the exact position of the front on
whether it will hang up in the Rolling Plains or be through the FA.
Independent of the eventual position of the front, convection will
be possible along the front near the dryline triple point and to the
northeast along the frontal boundary. The best chances for storms
within the FA would be in the southern Rolling Plains where the
front has greatest chances of slowing. Convection would be forming
within a moisture rich and very unstable environment under steep mid-
level lapse rates between 7-8 C/km. Mixed layer instability values
will be on the order of 3000 J/kg. Shear still looks to remain
fairly weak for May standards with deep layer shear vectors around
25kt. Therefore, the potential for large hail will exist with any
convection that develops.

Low level moist upslope flow will continue for Friday as the front
drags farther to the south. Cloudy and cool conditions will dominate
the area under this regime with shallow moisture present leading to
cooler temperatures. Light precipitation may be possible on Friday
within this post-frontal airmass. The next front will move through
Saturday morning bringing even cooler temperatures for the rest of
the weekend. Brief upper level ridging will move overhead from late
Friday into early Saturday. Upper level winds will then rapidly back
to the southwest in advance of the next short wave trough
approaching the region. Lift will spread over the area from about
00Z - 12Z Sunday then tapering off after 12Z as the short wave moves
east. With strong amounts of moisture within the atmospheric column,
there is a potential for heavy rainfall during the overnight hours,
especially for areas off the caprock. Sunday afternoon will see
rapid drying of the column above the lower levels as subsidence
spread overhead in the wake of the departing short wave. Lower
levels of the atmosphere will remain moist keeping low stratus in
for much of the day. The next short wave trough is currently progged
to skirt the area to the north on Monday bringing a return to dry,
westerly, and windy flow.

&&

.AVIATION...
(18Z TAFS)
Issued at 1219 PM CDT Wed May 1 2024

VFR will continue at KCDS, KLBB, and KPVW, for the next few hours
before thunderstorm chances increase by late afternoon at KPVW and
KLBB. Severe thunderstorms will be possible, and better confidence
exists with storms affecting KLBB compared to KPVW. Severe-caliber
wind gusts of 50 kt or greater will accompany storms in addition
to the potential for large hail surface and aloft. Convection will
clear KLBB and KPVW near 03Z tonight. Severe thunderstorms are
also forecast to affect KCDS tonight with gusts of 50 kt and
large hail, and clearing out after midnight. VFR will prevail
thereafter at all terminals with a cold front moving through all
terminals by late tomorrow morning.

Sincavage

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 11 PM CDT this evening for TXZ025-026.

&&

$$

SHORT TERM...09
LONG TERM....01
AVIATION...09