Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Tue Oct 21 2025 09:02:22

ACUS48 KWNS 210902
SWOD48
SPC AC 210900

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Tue Oct 21 2025

Valid 241200Z - 291200Z

....DISCUSSION...
....D4/Friday-D5/Saturday Southern Plains/ArkLaTex...
The shortwave trough over the southern Plains and associated surface
low/Pacific front will gradually move eastward Friday supporting
scattered thunderstorms over parts of TX/OK. Overnight convection
and continued low-level warm air advection is likely to impact the
environment to some degree. This suggests very low predictability
for any organized severe threat. Still, broad ascent, moderate
deep-layer shear, and the potential for destabilization suggests at
least some severe risk may develop from central OK southward toward
the Red River and central TX vicinity Friday.

Low-end severe potential will likely shift eastward into the
ArkLaTex and lower MS Valley D5/Saturday as the upper low moves
farther eastward. Most guidance shows the upper trough beginning to
weaken with the surface features also becoming more ill defined with
time. While the general environment likely will remain supportive of
thunderstorms and isolated severe potential, details are sparse.

....Eastern Plains and Mid MS Valley D6/Sunday-D7 Monday...
Higher severe potential may develop towards the end of the extended
forecast period as a Pacific trough and amplified westerly flow
develop over the western US D6/Sunday and move into the Plains and
Midwest D7/Monday. Substantial variability exists between multiple
ensemble and deterministic models regarding the evolution of the
trough and resulting surface pattern. More amplified and less
progressive solutions, along with some ML guidance, show the
potential for a deep surface low and strong cold front to develop
and sweep eastward. Should this occur, robust moisture return for
fall is likely to develop along with strong low and mid-level wind
fields across much of the central US. A favorable synoptic regime
could support widespread severe storm development with sufficient
instability/shear overlap for all hazards from the eastern Plains
into the MS Valley and Midwest.

This scenario remains highly uncertain with large variance noted
between both ensemble and deterministic solutions regarding the
structure and timing of the upper trough. Given the degree of
spatial and temporal variance, predictability remains too low to
justify probabilities in the extended forecast. However, 15% or
higher severe probabilities could be needed in future outlook cycles
should guidance trend towards a more unified/higher-end solution.

...Lyons.. 10/21/2025

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