Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Sat Sep 13 2025 06:24:29

AWUS01 KWNH 130624
FFGMPD
SDZ000-NDZ000-131200-

Mesoscale Precipitation Discussion 1080
NWS Weather Prediction Center College Park MD
223 AM EDT Sat Sep 13 2025

Areas affected...western ND into western/central SD

Concerning...Heavy rainfall...Flash flooding possible

Valid 130622Z - 131200Z

SUMMARY...Scattered thunderstorms with periods of embedded
training/backbuilding will pose a possible threat for flash
flooding over the northern High Plains through 11Z. Hourly
rainfall of 1.0 to 2.5 inches will be likely at times.

DISCUSSION...Area radar imagery over the northern High Plains at
06Z showed a NW to SE axis of thunderstorms advancing
northeastward from southwestern ND into west-central SD, along
with a few slower moving cells over northwestern ND. This activity
was located out ahead of a mid-level vorticity max and
southeastward extending shortwave trough axis located over WY.
Numerous smaller scale vorticity maxima were embedded within the
south-southwesterly flow aloft into the High Plains, out ahead of
the shortwave trough, helping to focus areas of thunderstorms
within areas of surface convergence beneath a diffluent and
divergent flow pattern in the upper levels. SPC mesoanalysis data
from 06Z showed CAPE of 1000 to 2000+ J/kg along with anomalous
PWs of 1.3 to 1.5 inches over the western Dakotas, but with only=20
a few small pockets of weak to negligible convective inhibition.
Easterly low level upslope flow was in place over portions of the
western Dakotas, aiding in convergence/ascent ahead of the
advancing convective segment tracking through southwestern
ND/west-central SD.

Synoptic and mesoscale forcing aloft, out ahead of the main
shortwave trough over the High Plains, combined with areas of
surface convergence will likely maintain scattered thunderstorms
over portions of the western Dakotas through the overnight, with
potential for redevelopment and expansion of thunderstorms over
western SD over the next 1-2 hours. While the evolution of
convection over the next few hours looks a bit messy, flash flood
guidance is relatively low over western SD and portions of western
ND, with values between 1 and 2 inches in an hour. Some exceedance
of these lower flash flood guidance values are expected with areas
of flash flooding possibly resulting over the next 3 to 6 hours.

Otto

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6GKoZSud3hJ1MyCTViP7Xnu6BfC3lmjcoymGD8vGRCfo0fthLRciCtdkckxTq6Wv1xs8=
JEjcDzs-5v7bI0U0z9Xbw5k$  for graphic product...

ATTN...WFO...ABR...BIS...UNR...

ATTN...RFC...KRF...MSR...NWC...

LAT...LON   49110306 49010183 48430157 47280102 46420029=20
            45369974 44050027 43280161 43530294 44290358=20
            45710357 47520386 48960373=20

=3D =3D =3D
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