ACUS01 KWNS 141244
SWODY1
SPC AC 141242

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0742 AM CDT Sat Sep 14 2024

Valid 141300Z - 151200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE NORTH-CENTRAL PLAINS...

...SUMMARY...
Thunderstorms capable of isolated severe gusts and hail will be
possible over parts of the north-central Plains.

...Synopsis...
Blockiness in the eastern CONUS will continue to dominate the
large-scale, mid/upper-level pattern through the period.  An
anticyclone will drift eastward to southeastward over the Great
Lakes, poleward of a broad belt of low heights and several embedded
vorticity maxima extending from the lower Mississippi Valley to
offshore from the Carolinas.  One of those perturbations will be the
decaying remnants of a merger of a midlatitude mid/upper low with
the remnants of Francine.  This feature is forecast to drift
erratically eastward to southeastward over the Mid-South,
contributing to convective potential over a broad area of the
Southeast, but with wind fields and lift too weak to support
organized severe potential.

Farther west, synoptic-scale height rises are forecast across most
of the central/northern Plains, as a strong trough digs south-
southeastward near the BC Coast and forms a 500-mb low near UIL at
the end of the period.  By then, associated cyclonic flow should
cover a large part of the CONUS west of the Rockies, as well as for
several hundred miles off the West Coast.

The 11Z surface analysis showed a low over northern MS (associated
with the remnants of Francine) with an occluded front arching across
AL to a triple point near MGM, a warm front across southern GA, and
a cold front across the western FL Panhandle.  These boundaries
should become more diffuse with time today as the deep-layer cyclone
above the low continues its gradual degradation.  Meanwhile, a
quasistationary front from east-central ND across central SD to
southwestern NE should weaken through the day, but with a remnant
trough/convergence zone lingering near the present position.  A weak
surface low should form farther west today, in northeastern WY east
of GCC, then migrate eastward into western SD toward RAP tonight.

...North-central Plains...
Isolated to scattered thunderstorms are expected to develop this
afternoon, in a narrow corridor of relatively maximized low-level
convergence (corresponding to the weak front/trough) and favorably
strong surface heating east through southeast of the low.  Isolated
severe gusts and hail will be possible as convection proceeds across
SD and perhaps into southern ND this evening, before encountering
progressively more-stable low-level conditions with a decreasing
severe threat.  A weak perturbation apparent in moisture-channel
imagery over east-central WY should move northeastward across the
western NE Panhandle to southwestern/south-central SD by mid/late
afternoon, and may contribute subtle large-scale ascent to the
environment.  Still, with broader, ambient height rises superimposed
on that, considerable mesoscale timing/location uncertainty remains
on the most probable initiation zone within the southern part of the
outlook area.  The later initiation occurs, the farther north the
unconditional severe-threat area will be.

Activity should move north-northeastward into a corridor of
favorable moisture and buoyancy, with peak MLCAPE in the 500-1500
J/kg range, atop a well-mixed subcloud layer.  Greater lift and more
backing of low level flow will be present over the SD part of the
outlook, spreading northward into southern ND with time this
evening, and supporting conditional potential for upscale growth of
activity initiating in a hotter boundary layer near the Badlands.
Stronger capping and weaker convergence over western NE cast some
doubt as to formation and convective coverage in the Sandhills,
though the environment will be favorable for marginal severe there
as well.  Modest low/middle-level winds nonetheless will veer
strongly with height, leading to 25-35-kt effective-shear magnitudes
in support of some organization.

..Edwards/Mosier.. 09/14/2024

$$
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