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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