577
FXUS64 KLUB 191059
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
559 AM CDT Thu Sep 19 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 304 AM CDT Thu Sep 19 2024

Even with three days left until the first day of fall, our heatwave
only ramps up today and may tie the daily record high at Childress.
Temperatures at 1 AM in the upper 70s and low 80s were closer to our
normal highs for the date thanks to muggy southeast winds supplying
dewpoints in the upper 60s. This moisture will unfortunately mix out
this afternoon as winds veer southwesterly in response to a surface
low exiting eastern CO for the greener pastures of eastern KS. Add
to this a marked increase in mid-level subsidence courtesy of a
sprawling upper high centered near the Big Bend and the stage will
be set for even hotter temps today, including a potential record
high at Childress. Prospects for deep convection today are slim in
light of the aforementioned negative factors, so will disregard the
majority of CAMs that insist on storms along a very weak surface
trough/dryline forecast to settle over our N-NW zones later today.
Southerly breezes won`t be quite so muggy tonight, yet lows will
still fare 8-12 degrees above normal.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 304 AM CDT Thu Sep 19 2024

At the beginning of the period, the mid/upper-level pattern will
feature an amplifying, southern-stream, positively-tilted trough
digging into the Desert Southwest following the collapse of the
synoptic-scale gyre previously anchored over the western U.S. days
prior; and this trough will be accompanied by a 250 mb jet streak
near 100 kt rounding its base and ejecting towards the Four Corners
region on Friday. A coupling of the mid- and high-level flow should
occur as a northern-stream trough noses into the Glacier Country,
resulting in further amplification of the synoptic-scale flow and a
substantial elongation of the 250 mb and 500 mb jet streaks. The
subtropical ridge will also shift northward over southern Texas
while slanting into a southwest-to-northeast-oriented manner via the
influence of the upstream troughing. Farther east, the trough
located across the eastern seaboard will be slow to progress but is
forecast to gradually lose its amplitude even as a pseudo-Rex Block
is restored over the northeastern U.S., maintaining a weakened
blocking pattern across the Lower 48. Geopotential height tendencies
will be neutral for most of the day Friday before becoming slightly
negative towards the late-afternoon hours as the trough begins to
attain its neutral-tilt over the northern Sonoran Desert.

At the surface, a quasi-stationary front will be positioned along
the lee of the southern Rocky Mountains, and bend northeastward
towards the northern TX PH and OK PH where lee cyclogenesis should
be underway. Leeward pressure falls will be moderated by the neutral
geopotential height tendencies aloft; however, southerly winds will
become breezy as the mass fields begin to respond to the amplified
troughing to the west. The CWA will be enveloped within the moist
sector, though deep boundary-layer mixing will temporarily delay the
more-rapid surge of moisture return expected to occur the following
day. Intense dry-bulbing will occur even as cirrus bands advect over
the CWA from the southwest, with high temperatures similar to
Thursday while remaining below record values. The subsidence layer
in the mid-levels will also begin to erode as flow steadily backs to
the southwest, but the magnitude and depth of dry air throughout the
columns combined with the residual subsidence layer, in addition to
the lack of low-level convergence, will result in a dry forecast on
Friday afternoon and night. PoPs were removed from the western areas
as the scattered convection in New Mexico will remain west of the
TX/NM state line due to the orientation of the steering flow.

By Saturday morning, the neutrally-tilted trough will continue
pivoting over the Desert Southwest, with a well-defined, mid- and
high-level closed low present as it emerges over the Four Corners
region. NWP guidance is also indicating the 250 mb jet streak
strengthening to near 110 kt as it ejects over central New Mexico on
Saturday morning. The position of the 700 mb trough should also be
located west of the TX/NM state line at this time, but WAA-induced
showers and storms may advect into the far southwestern TX PH by
daybreak Saturday. Rapid moisture return will occur during the
overnight hours Friday into Saturday as leeward pressure falls
intensify, with a plume of middle 60 degree dewpoints advecting
poleward across the entire CWA by the mid-morning hours. Southerly
winds will strengthen further compared to Friday, and winds were
raised a couple of kt from the blended initialization as 998 mb
surface low forms beneath the core of the jet streaks aloft. The
closed low embedded within the trough should rotate over the Four
Corners by Saturday afternoon, and the superposition of the mid- and
high-level jet streaks will result in the CWA being beneath the
right-entrance region as the afternoon progresses on Saturday. The
initiation of isolated storms across the open moist sector will be
possible, but most of the convection should be focused along the
incoming cold front from the west as it overtakes the dryline.

PoPs have once again increased slightly from the previous forecast
assessments, with the highest coverage of storms delineated across
the far southwestern TX PH and northwestern South Plains before
storms becoming more-scattered with southward extent (as indicated
in prior prognostications). A squall line will be possible, but the
potential exists for updrafts to be sheared apart with southward
extent across the CWA given the magnitude of cloud-layer flow
despite favorable low-level storm-relative inflow facilitating wide
updrafts. Severe-caliber wind gusts will be possible, especially if
a squall line forms, given Inverted-V boundary-layer profiles and
sufficient loading of hydrometeors. The risk for large hail should
be tempered due to warm-cloud depths near 14 kft as the steepest
geopotential height falls/mid-level cooling remains displaced to the
north of the CWA, but a rogue nickel-to-quarter size hail event
cannot be ruled out. The highest storm chances are forecast during
the afternoon and into the late-evening hours across the Caprock
Escarpment, and timing will continue to be refined in forthcoming
cycles. The arrival of a polar cold front is also forecast to occur
during the early-morning hours Sunday, and its southward movement
may be reinforced by outflow from convection across the west-central
High Plains, which would result in a faster progression than what is
currently indicated in the official forecast.

The low PoPs for Sunday were trimmed slightly from the blended
initialization and eliminated after midnight CDT as the front should
clear the CWA by then, with the best chances for storms across the
Rolling Plains. The first day of fall will be accompanied by much
cooler temperatures, and highs were nudged a couple of degrees lower
with a 30-percent weighting of the 00Z statistical guidance applied
to the NBM as the thinking continues to trend towards a faster
frontal progression. Benign and mild weather is forecast for Monday
as a weak surface high settles into the region, with renewed chances
for storms returning by the middle of the week as global NWP
guidances in agreement with at least broadly cyclonic flow
encompassing the central U.S., but there remains significant
bifurcation with respect to the amplitude of the troughing and
whether or not it remains open. Therefore, the low, blended PoPs
were maintained through the end of the forecast period as
predictability remains limited.

Sincavage

&&

.AVIATION...
(12Z TAFS)
Issued at 559 AM CDT Thu Sep 19 2024

Continued VFR with light winds through tonight.

&&

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

$$

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