Storm Prediction Center Mesoscale Discussion 1879

   Mesoscale Discussion 1879
   NWS Storm Prediction Center Norman OK
   0117 PM CDT Sun Aug 11 2024

   Areas affected...Portions of southwestern SD and northwestern NE

   Concerning...Severe potential...Watch possible 

   Valid 111817Z - 112015Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Portions of southwestern South Dakota into northwestern
   Nebraska are being monitored for a possible Severe Thunderstorm
   Watch.

   DISCUSSION...Isolated to widely scattered thunderstorms are evolving
   over far northeastern WY and over the Black Hills early this
   afternoon -- likely aided by ascent preceding a midlevel shortwave
   trough (and associated MCV) tracking eastward across southwest MT,
   and heating over the higher terrain. Continue diurnal
   heating/destabilization amid middle/upper 50s to lower 60s dewpoints
   will continue to erode boundary-layer inhibition and contribute to
   500-1000 J/kg MLCAPE. This, coupled with long/mostly straight
   hodographs (around 40-45 kt of effective shear), will support a
   gradual increase in thunderstorm intensity/organization through the
   afternoon. The primary concern with any initial
   semi-discrete/splitting supercell structures is large hail
   (generally 1.5-1.75 inches) and locally severe gusts. Thunderstorms
   will generally track southeastward into northwestern Nebraska
   through the afternoon, where continued heating will support a
   corridor of sufficient (albeit weak) surface-based instability for a
   continued severe risk. 

   There is uncertainty on the overall coverage of severe thunderstorms
   across the area, and the need for a watch is uncertain.

   ..Weinman/Hart.. 08/11/2024

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...LBF...UNR...CYS...

   LAT...LON   43810397 44330401 44510388 44650348 44600304 44410225
               44060146 43400067 42800059 42200073 41920133 41770240
               41950340 42380361 43370387 43810397