ACUS11 KWNS 171959
SWOMCD
SPC MCD 171958
SDZ000-172200-

Mesoscale Discussion 2012
NWS Storm Prediction Center Norman OK
0258 PM CDT Mon Aug 17 2026

Areas affected...much of central South Dakota

Concerning...Severe potential...Watch possible

Valid 171958Z - 172200Z

Probability of Watch Issuance...60 percent

SUMMARY...Organizing thunderstorm development may pose increasing
potential to produce large hail and damaging wind gusts into the 6-7
PM CDT time frame. A severe weather watch probably will be needed
at some point, though how soon remains somewhat unclear.

DISCUSSION...Thunderstorm development has been increasing across the
high plains near and to the north of the Black Hills vicinity into
southwestern North Dakota. Based on the latest Rapid Refresh
output, it appears that this is being aided by forcing for ascent
associated with weak lower/mid-tropospheric warm advection, to the
south of larger-scale mid-level troughing digging southeast of the
Canadian Prairies through the international border area. With
further progression of this trough, west-northwesterly flow in the
700-500 mb layer is forecast to strengthen in a belt of across
southeastern Montana through north central South Dakota into early
evening.

Within this regime, ongoing storms are likely to continue a general southeastward propagation, with potential to undergo substantive
further intensification and upscale growth. An increasingly moist
low-level environment into and across the middle Missouri Valley
around Pierre may support updraft inflow increasingly characterized
by CAPE in excess of 1500-2000+ J/kg, in the presence of
strengthening deep-layer shear. This probably will contribute to
evolving supercell structures with potential to produce large hail
and damaging wind gusts, which could consolidate into an upscale
growing cluster by early evening.

..Kerr/Guyer.. 08/17/2026

...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fjg!7Vfa4yxGE8sebWYLHCYPy56chtkRS3HGKd3tilLpZdQ5gNpIfYpAYOi4qbO15xz1jG9q4ON6xEPZPHxYgwpMIGmx9a4$ for graphic product...

ATTN...WFO...FSD...ABR...UNR...

LAT...LON 45920223 45579932 45059774 43479935 44120213 44270314
45100252 45920223

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN


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