SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1223 PM CDT Thu May 11 2023
Valid 121200Z - 131200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THE MID-MISSOURI
RIVER VALLEY AND ACROSS THE SOUTHERN PLAINS TO THE RIO GRANDE
VALLEY...
...SUMMARY...
Strong/severe storms are expected to begin during the afternoon,
across a broad area extending from the Mid-Missouri Valley southward
to the Rio Grande Valley. Very large hail and damaging wind gusts
will likely be the primary severe threats over the southern half of
the area into the overnight hours, while damaging winds and hail,
and a couple of tornadoes, will be possible across the Mid Missouri
Valley area through the evening.
...Synopsis...
The upper-level wave currently migrating northeast across western KS
is forecast to continue to the northeast over the next 48 hours,
reaching the mid-MO Valley by mid/late afternoon. In general, this
feature, and an attendant surface low, will de-amplify through the
period with an associated weakening of mid/upper-level flow outside
of the mid-MO Valley. A surface trough/dryline should be draped from
eastern NE southward through central KS/OK and into TX by late
afternoon and will act as a foci for convective initiation. To the
south, mid-morning water-vapor imagery depicts a shortwave trough
approaching Baja CA. This wave should reach the Big Bend region by
tomorrow afternoon/evening, and will augment orographically-driven
ascent, fostering scattered thunderstorm development along the Rio
Grande.
...Mid Missouri River Valley...
A reservoir of low 60s dewpoints is noted in morning surface
observations across much of the central Plains. Persistent
south/southeasterly flow over the next 36 hours ahead of the
approaching surface low will maintain some poleward moisture
advection, and some solutions suggest dewpoints may reach the
mid-60s. Regardless, cool temperatures aloft associated with the
upper-low will result in mid-level lapse rates near 7-7.5 C/km.
Combined with the aforementioned low-level moisture, this should
support MLCAPE values approaching 2000-3000 J/kg by late afternoon.
Given the lack of an appreciable EML, diurnal warming should erode
any mixed-layer inhibition and allow convective initiation along the
surface trough/dryline.
Initial convection will likely manifest as an arching band of
discrete/semi-discrete cells with an attendant hail/wind risk. A few
tornadoes are also possible given veered low-level winds and modest
effective SRH ahead of the dryline. Upscale growth into one or more
organized clusters is probable through the evening given deep-layer
meridional flow oriented largely along the boundary - especially
across southeast NE into adjacent areas of IA, KS, and MO. A
corridor of several, perhaps longer-lived, supercells may emerge
across portions of northeast NE where deep-layer shear orientations
will be nearly orthogonal to the dryline. If this scenario occurs
the large hail/tornado threat may be locally maximized. A
significant hail area has been introduced to reflect the conditional
nature of the threat. However, confidence in the spatial extent of
this threat appears too limited in this forecast cycle for a
categorical upgrade.
...Central OK to the Rio Grande...
A migratory dryline should be draped from northeast KS through
central OK and into western TX by late afternoon, though forecast
uncertainty remains somewhat high in the exact placement of this
feature by peak heating. This region will be well displaced from the
stronger forcing for ascent to the north, but forecast soundings
suggest residence time within the dryline circulation and strong
diurnal warming will be sufficient for convective initiation along
the boundary. Additional cells will likely develop off the terrain
in northern Mexico, and should migrate east/northeast into southern
TX.
High-quality moisture return (dewpoints into the low 70s), coupled
with temperatures in the low 80s will support strong buoyancy
(MLCAPE near 4000 J/kg in some guidance). Mid and upper-level winds
are forecast to be modest, only around 25-30 knots, but may be
adequate for storm organization - especially across central/southern
OK. Further south towards the Rio Grande, hodograph structure
becomes more nebulous amid weak flow aloft, but the combination of
ample buoyancy and a deep, well-mixed boundary layer will support
the potential for strong downburst winds and large hail with initial
updraft pulses.
Through the evening, initially discrete/semi-discrete cells will
likely see cold pool amalgamation/consolidation, resulting in
upscale growth into a loosely organized, cold-pool driven MCS. As
this occurs, the potential for severe winds should increase across
central TX. The strengthening of a low-level jet over southern TX
may allow for MCS maintenance overnight to near the TX Coastal Plain
by 12 UTC Saturday (though the intensity of the MCS with eastward
extent remains uncertain).
..Moore/Leitman.. 05/11/2023
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