SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0648 AM CST Thu Nov 07 2024
Valid 071300Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WEST TEXAS...
...SUMMARY...
Large hail, isolated severe thunderstorm gusts, and a tornado or two
are possible this evening and tonight across parts of west Texas.
...Synopsis...
A closed and temporarily cut-off, mid/upper-level cyclone was
drifting eastward to southeastward over the Desert Southwest and
Four Corners regions, and centered near INW. A large, well-
developed, baroclinic-leaf formation was apparent in IR and
moisture-channel imagery in its eastern semicircle, across much of
NM and CO, and extending across the central High Plains. The 500-mb
low is forecast to move slowly to central NM through the period,
while a shortwave trough now north of the low pivots around the
southern/southeaster side of the cyclone tonight. Associated height
falls and large-scale ascent will gradually overspread west TX and
the southern High Plains, both in the form of DCVA nearer to the
cyclone core, and warm advection over much of the southern Plains to
its east.
Meanwhile, per latest NHC forecasts, Hurricane Rafael will continue
to move westward away from the Keys and Cuba, toward the central/
south-central Gulf. This will occur south of an arc of mid/upper
ridging extending from the subtropical Atlantic across FL and the
north-central to southwestern Gulf.
At the surface, the key feature for today's forecast will be a cold
front -- drawn at 11Z from the Ohio Valley across central AR, to
near a TXK-ERV line and becoming stationary to warm westward to a
low near the Rio Grande, south of 6R6. Another low was drawn
between MAF-FST, and warm frontogenesis apparent to its east-
southeast likely will persist and result in effective northward
displacement of the western segment of the main frontal zone with
time today. As the aforementioned shortwave trough pivots toward
the region, surface cyclogenesis is expected over the lower Pecos
Valley/Permian Basin region of west TX, consolidating the previously
elongated, multi-centered low-pressure area. The low should move
northward or north-northeastward tonight, toward the Caprock region
of northwest TX, with a cold front to its south extending to the Big
Bend region. Meanwhile, the warm-frontal segment should advance
northward over west-central TX, though considerable mesoscale
uncertainty remains as to how far, given:
1. The strength of the ambient continental/polar airmass to its
north and
2. Probable reinforcement by convection/precip on the cool side
much of today.
...West and central TX...
Predominantly elevated thunderstorms are expected to develop today
and gradually increase in coverage while moving northward over
central and northwest TX, in a weakly capped plume of strengthening
warm advection, moisture transport and ascent to LFC. Isolated
severe hail is possible with this activity, though lack of
substantial buoyancy should limit overall severe potential to
marginal in coverage and intensity.
As that process continues, a diurnally heated slot of return-flow
boundary-layer air, containing increasingly unstable, surface-based
parcels, will spread from south-central TX, the Rio Grande Valley
and the southern Hill Country northwestward toward the frontal and
cyclogenetic regimes. Diurnal heating and moist advection are
expected to yield favorable warm-sector destabilization. Surface
dewpoints increasing into the low 60s F in northern areas and upper
60s to near 70 F over southern parts of the outlook will yield
peak/preconvective MLCAPE in the 1500-2000 J/kg range ahead of the
cold front and south of about I-20, with sharp reductions across the
front toward the upper cyclone, and northward into the ambient
rain-cooled airmass.
Meanwhile, large-scale ascent will continue to increase gradually on
both sides of the front, peaking late overnight. These processes
will support isolated to scattered thunderstorm development from
late afternoon into tonight, along the front and over higher terrain
in the Big Bend region. Some of this activity may be supercellular
for a few hours, with all severe hazards possible. Forecast
hodographs indicate some tornado potential, especially near the low
and if a discrete storm can interact with a favorably aligned
segment of the front while maintaining warm-sector surface inflow.
Aforementioned mesoscale uncertainties preclude a more-focused,
unconditional 5% tornado area at this time. The delay in the
strongest forcing for ascent after the peak buoyancy and the
potential for evolution to extensively messy modes also renders
tornado potential quite conditional. Convective coverage overall
should increase to scattered/numerous, expand to both sides of the
front as cooling aloft overspreads the region, and render much
messier convective mode. Large hail will be possible on either side
of the front, especially with relatively sustained/discrete cells,
and damaging gusts will be most probable with convection moving
into/through the warm sector.
..Edwards/Mosier.. 11/07/2024
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