Area Forecast Discussion
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FXUS64 KLUB 281118

Area Forecast Discussion
National Weather Service Lubbock TX
618 AM CDT Thu Sep 28 2023

...New AVIATION...

(Today and tonight)
Issued at 232 AM CDT Thu Sep 28 2023

A general pattern of troughing in the west and ridging east is set
up across the CONUS this morning. The Pac NW trough should make
its way to the front range of the northern Rockies by Friday
morning resulting in a mild backing of our upper level wind
fields. The subtropical jet remains weak and well to our south
yielding little influence in terms of sensible weather for us. Put
simply, there is little assistance, from a synoptic scale, for
storm development across the region over what we`ve seen the past
few days. Once again, we see nearly saturated conditions around H7
with modest instability indicated (~500-700J/kg) of MUCAPE. The
mid-levels will also introduce all sorts of dry air entrainment
complications. So, we have the moisture and instability but not
any solid source of lift. H7 frontogensis fields have a
substantial number of potential areas of linear, meridional lines
of lift across the region. However, confidence in model abilities
to resolve and correctly place these features remains low. So, we
have an airmass that is on the verge of supporting mild convection
with ambiguous forcing mechanism. In the subcloud layer, it`s a
classical inverted V signature during the afternoon/early evening
which will subject to strong evaporational processes. As such, the
most common mode is likely to be virga. At this point, the
prospects for an honest storm remains too uncertain (1. will it
form and 2. where) to advertise a mentionable POP. The possibility
is there, however...someone might get lucky. Beneath the virga, a
downburst wind potential will exist though we have not seen much
strong potential in recent days. Alas, there is much about the
atmosphere we simply cannot measure sufficiently to be more
certain in these borderline sensible weather situations. If
anything, based on sfc theta-e values, areas west of the Caprock
Escarpment may have a slightly better shot at seeing convective


(Friday through Wednesday)
Issued at 232 AM CDT Thu Sep 28 2023

A relatively active weather pattern is forecast to return to the CWA
through the entire extended period. An amplifying, positively-tilted
trough will dig into the western U.S. on Friday following an
anticyclonic wave break over the far northeastern Pacific Basin,
where an intense, meridional jet streak near 140-150 kt translates
southward along the Pacific coastline. The quasi-zonal, subtropical
jet stream is expected to be juxtaposed to the base of this
developing trough, and phasing of the two jet streaks is forecast to
occur heading into the weekend. On Friday, the northern periphery of
the subtropical ridge will eclipse the CWA where weakly difluent
flow will be present as a subtle shortwave perturbation translates
through the apex of the ridge. The gradual increase in large-scale
forcing for ascent over the central Rocky Mountains is expected to
result in lee cyclogenesis across southeastern Colorado on Friday.
Sharpening of the surface trough will follow with a breezy day
across the region with southerly winds between 15-25 mph, though
vertical mixing heights are expected to be shunted by the 700 mb
trough advecting a warm nose (cap) overhead. Gradual geopotential
height rises on the backside of the shortwave perturbation as it
translates through the apex of the ridge is expected to suppress
convective development by mid-level substance, nullifying any
potential for thunderstorm development on Friday afternoon despite
the intense heating where temperatures in the lower 90s are
expected, which is about 10 degrees above seasonal norms.

A large, and expansive, baroclinic cyclone is set to form over the
southern Great Basin over the weekend as a well-defined PV streamer
rotates southward following the breaking wave event. Large-scale
forcing for ascent will increase accordingly over the southern Rocky
Mountains and into West Texas; however, mid- and high-level flow is
expected to attain a sharp, meridional (poleward) component on
Saturday even as the subtropical jet stream phases with the highly
amplified trough. PoPs have been trimmed westward, as the thinking
is that the bulk of showers and thunderstorms will occur west of the
Texas/New Mexico state line while more widely-scattered convection
clips the western South Plains and the extreme southwestern Texas
Panhandle. The best potential at this time for thunderstorms on
Saturday is forecast to be near and west of the HWY-385 corridor,
and semi-organized convection will be possible with some storms
capable of producing locally strong-to-severe-caliber gusts in
addition to brief downpours. Thunderstorm chances are also forecast
to expand area-wide heading into Sunday as guidance continues to
indicate that the 500 mb low will remain in an unsteady state and
potentially transition into an open trough as fast as it became a
closed system. The reason for this is an upstream jet streak
translating eastward into the Pacific Northwest/British Columbia
where the possibility exists of a coupled jet developing over the
Great Basin. Increasing high-level difluence in concert with the
ejection of embedded shortwave perturbations yields the possibility
for perhaps a few bands/clusters of showers and thunderstorms to
develop across portions of the CWA on Sunday, and most of the
convection is expected to remain west of the TX/NM state line.

All global NWP guidance suites have come into better agreement with
respect to when the 500 mb closed low transitions into an open
trough over the western U.S. interior. The trough is forecast to
become entirely open by Monday as the aforementioned jet streak over
the Pacific Northwest translates southward along the eastern
periphery of a strong, mid/upper-level ridge over the northeastern
Pacific Ocean. This should result in the positively-tilted trough to
eject eastward, amplifying the component of mid- and high-level over
the CWA as the right exit-region of the 250 mb jet streak translates
over the Caprock. PoP chances have increased slightly from the
previous assessments, and have been accepted as prospects for
potentially multiple rounds of showers and thunderstorms appear more
favorable throughout the early and middle part of next week. PoPs
will dwindle following the departure of the mid/upper-level trough
by the latter part of the work week, and NWP guidance remains
bifurcated on the state of the upper air pattern by the end of next
week and beyond the scope of the forecast period (D8/Thursday). At
the very least, a gradual cooling trend is forecast by the middle
of next week with temperatures hovering closer to seasonal norms.



(12Z TAFS)
Issued at 559 AM CDT Thu Sep 28 2023

VFR next 24 hours. Some virga showers will be possible this
afternoon. Underflight of virga is discouraged given the downburst
potential. Plenty of low level thermal turbulence this afternoon
possibly smooth above 10kft AMSL.




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