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 www.spc.noaa.gov 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