624
FXUS64 KLUB 181731
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
1231 PM CDT Wed Sep 18 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 316 AM CDT Wed Sep 18 2024

Satellite imagery at 2 AM revealed the tail-end of an upper trough
lifting northeast across the Panhandles well south of a stacked
cyclone in southern Montana. In the wake of this trough, modest
height rises will unfold over our area today within weak westerly
flow aloft. Low-level moisture remains respectable today on S-SE
flow ahead of a surface trough and diffuse dryline that shifts to
near an AMA-HOB line by mid-afternoon. Finer res models are in good
agreement that temps in the low/mid 90s near the boundary will push
CIN to negligible values, so NBM`s dry PoPs won`t make the cut
today. Combined with MLCAPEs around 1200 J/kg and upwards of 35
knots of cloud depth shear, the stage will again be set for another
round of severe storms including supercells. Higher LCLs today will
fuel even greater DCAPEs in excess of 1500 J/kg, so downbursts
remain the primary concern followed by some severe hail potential.
Limited background forcing looks to keep most storms from running
too far beyond sunset, so will keep PoPs dry after 06Z. Another mild
and rather muggy night awaits on steady S-SE winds with clearing
skies.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 316 AM CDT Wed Sep 18 2024

The mid/upper-level pattern will remain amplified at the start of
the period as the cyclonic gyre located over the western U.S. begins
to dissipate. Dissipation of this gyre will occur after the ejection
of the negatively-tilted trough pivoting over the northern Great
Plains as it becomes absorbed into a longer-wave trough over far
northern Canada. Farther southwest, a positively-tilted trough will
continue to dig into the Pacific coastal region and begin pivoting
over the Sierra Nevada Mountains as a mid- and high-level closed low
forms; and will be accompanied by 250 mb and 500 mb jet streaks near
100 kt and 50 kt, respectively, rounding its base. The blocking
pattern over the Lower 48 will remain somewhat intact as a remnant,
post-tropical low over the eastern U.S. becomes absorbed into an
open trough, while the center of the subtropical ridge over central
Mexico shifts northward into southern Texas via modulation of the
amplifying trough to the west. Large-scale subsidence in the mid-
levels will increase further from the prior day, with a nearly 100
mb deep subsidence layer advecting over the CWA as the northern
periphery of the subtropical ridge eclipses West Texas.

At the surface, a quasi-stationary front is forecast to be located
west of the TX/NM state line, with a weak, lee cyclone rotating
across southeastern New Mexico and the dryline extending southward
from the low. The quasi-stationary front should bend northeastward
into the TX PH/north of the CWA, connecting to another lee cyclone
along the KS/OK state line before branching northward as an occluded
front that extends to the vertically-stacked low in southern Canada.
The CWA will remain in the moist sector on Thursday, and despite the
positive geopotential height tendencies, leeward pressure falls will
be maintained with surface winds remaining slightly veered of south.
Intense heating is expected with a deeply-mixed boundary-layer
profile developing, with PBL heights ascending to above 700 mb
before encountering the deep subsidence layer aloft. Convergence at
the surface and low-levels is forecast to be displaced to the west
and north of the CWA (e.g., nearest the front), and while the
development of a cu field should occur by peak heating, the lack of
foci for convergence and the magnitude of the mid-level subsidence
layer will prevent cu from transitioning into cBs. The forecast
remains dry for Thursday despite the QPF signal from the HREF as all
indications otherwise point towards the suppression of deep
convection.

The positively-tilted trough to the west of the CWA is forecast to
pivot into the Desert Southwest by late Friday, further modulating
the amplitude and position of the subtropical ridge over the State
of Texas. There remains excellent agreement among the guidance with
respect to the superposition of the 250 mb and 500 mb jet streaks
over the Intermountain West and into the northern Great Plains, as
these features will become elongated via the effects of coupling
from a northern-stream jet streak emerging over southern British
Columbia. The subtropical ridge over the region will attain a
southwest-to-northeast-oriented position as the upstream trough
begins its transition to a neutral-tilt. Scattered-to-numerous
thunderstorms should form along the lee of the southern Rocky
Mountains, but the south-southwesterly-to-southwesterly component of
the steering flow is expected to keep convection west of the TX/NM
state line on Friday. PoPs were removed for Friday evening storms
should be delayed in arriving into the CWA until the early morning
hours Saturday as geopotential heights begin to fall.

PoPs generated by the NBM have increased on Saturday compared to the
previous assessments, and further adjustments to the PoPs were made
to expand the 40-percent contour into the I-27/HWY-87 corridors as
confidence continues to increase in at least scattered convection
forming across the Caprock Escarpment on Saturday. By this time, the
neutrally-tilted trough will begin to emerge over the southern Rocky
Mountains while the mid- and high-level closed low remains intact,
with indications of the trough becoming negatively-tilted by the
afternoon hours. Rapid-intensification of the 250 mb flow will occur
throughout a 12-hour period as the core of the related 100 kt jet
streak translates over northeastern New Mexico, resulting in intense
divergence and isentropic ascent. Low-level convergence and ascent
will be further aided by frontogenetical forcing from the cold front
to the west, with an expectation for scattered to potentially
numerous thunderstorms to develop and form into a broken line on
Saturday afternoon across the Caprock Escarpment. Some storms may be
severe on Saturday, with a primary hazard of damaging wind gusts.
It appears that the highest coverage of storms should be across the
far southern TX PH, with storms becoming more-scattered with
southward extent as large-scale forcing for ascent lessens due to
the negatively-tilted trough pivoting poleward into the west-central
Great Plains heading into Saturday night. A further increase in PoPs
may be necessary in forthcoming forecast cycles as mesoscale
guidance comes into range.

The system is forecast to dampen in amplitude heading into Sunday as
begins to dissolve into an open trough over the central Great
Plains. The position of the cold front may be farther southeast than
what the current NWP guidance is indicating, especially due to the
likelihood of its movement being convectively-reinforced by outflow
from the night prior. The dry forecast generated by the NBM has been
maintained, but depending on how incoming guidance handles the
frontal position, an introduction of low PoPs may be necessary for
the southeastern zones on Sunday. Thereafter, global NWP guidance
has significantly diverged on the state of the upper air pattern for
early next week compared to the previous prognostications. Low PoPs
are reflected in the forecast by mid-week, and have been maintained
as predictability becomes limited by the end of the forecast period.

Sincavage

&&

.AVIATION...
(18Z TAFS)
Issued at 1227 PM CDT Wed Sep 18 2024

VFR expected to prevail through this TAF period. Potential still
exists for some iso-sct TSRA to develop during the mid to late
afternoon hours mainly north of a line from LBB to CDS, but
confidence in eventual areal coverage of this convection remains
too low to include TS mention in any TAF at this time. Strong and
erratic downburst winds should be expected in the vicinity of any
TS, with convection diminishing after sunset and VFR continuing
overnight through Thursday.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...93
LONG TERM....09
AVIATION...30