Day 1 Severe Weather Outlook

Valid 201300Z – 211200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
THE TEXAS PERMIAN BASIN AND SOUTH PLAINS TO THE SOUTHEASTERN TEXAS
PANHANDLE AND SOUTHWESTERN OKLAHOMA…

…SUMMARY…
Isolated severe gusts and/or hail are possible this afternoon from
parts of the Texas Permian Basin and South Plains to the
southeastern Texas Panhandle and southwestern Oklahoma.

…Synopsis…
In mid/upper levels, a split-flow pattern will become more
pronounced through the period, as a cyclone now over coastal central
CA enlarges and becomes more detached from the prevailing
westerlies. The low should pivot southeastward over southern CA
than east-northeastward, moving to near the southern NV/CA border or
LAS area by 12Z. As associated height falls spread across the Great
Basin, Southwest deserts, and southern Intermountain region, a
leading shortwave trough now over AZ/Sonora will eject northeastward
and weaken. The latter perturbation should cross much of NM and
southern CO through the day, reaching eastern CO and the southern
High Plains by 00Z. It then will penetrate a synoptic ridge and
enter the northern stream, ahead of a progressive trough that will
be crossing MT/Dakotas and the Canadian Prairie Provinces. By 12Z,
the ejecting shortwave trough should reach IA and northern MO.

At the surface, lee troughing is becoming better defined up and down
the High Plains, with an attached low analyzed over northeastern CO
between ITR-AKO. By 00Z, the low should be over south-central/
southeastern NE near JYR, with a cold front arching across
northeastern KS and east-central CO. By 12Z, the low should deepen
ahead of the ejecting shortwave trough, reaching southeastern
MN/northeastern IA. The cold front should be located from there
across northwestern MO, eastern KS, northwestern OK, and
east-central NM.

…Southern Plains…
Widely scattered to scattered thunderstorms should develop in a
north-northeast/south-southwest band early this afternoon across
parts of west TX and the South Plains region. This activity should
expand lengthwise, while moving northeastward into progressively
greater low-level moisture, and impinging on at least a narrow
corridor of supportive surface-based buoyancy. Damaging gusts and
large hail will be possible. The hail threat may extend somewhat
north of the wind potential, atop weaker to no surface-based
instability.

Mass response to the western troughing at multiple scales will
include a broad slab of warm-sector return flow, including low-level
warm advection and partial moisture recovery. Surface dew points
should increase to the 60s F prior to cold-frontal passage across
much of central TX into southern/central OK, with 50s in the
more-proximal, preconvective environment over west-central/northwest
TX. Low-level destabilization/lapse rates will be limited by the
presence of antecedent clouds/precip, already apparent in satellite
and composited radar imagery over much of the outlook area. Behind
this mess, however, a narrow corridor of steep midlevel lapse rates
and at least marginally supportive boundary-layer instability may
develop, supporting up to 500-1000 J/kg MLCAPE shortly preceding the
convective band. With a broad area of strong mid/upper-level winds
supporting 40-50-kt effective-shear magnitudes, organized multicells
and a few at least transient supercells are possible. Activity
overall should weaken this evening as it outruns the surface-based
buoyancy into western OK and northwest/north-0central TX.

…Southwest TX/DRT region…
Isolated to widely scattered thunderstorms may develop this
afternoon over the Serranias del Burro and adjacent high terrain of
northern Coahuila. Vertical shear over this area will be supercell-
favorable (conditionally), characterized by strongly veering flow
with height and enlarged hodographs in the 0-3-km layer. While the
greatest associated severe threat would be on the Mexican side, any
sustained thunderstorm(s) still may pose a severe risk if/when
reaching the Rio Grande near DRT, based on probable east-northeast/
right-moving storm motions. However, considerable uncertainty
exists on storm longevity at severe levels, given: 1) the heavy
orographic dependence of development and 2) the presence of stout,
EML-related capping downshear in the observed 12Z DRT RAOB and
forecast soundings. A small severe area may be needed in a later
outlook if unconditional confidence increases in such convection
penetrating into TX with hail/wind above severe limits.

..Edwards/Mosier.. 11/20/2019

$$

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