Mesoscale Discussion 1155
   NWS Storm Prediction Center Norman OK
   0134 PM CDT Mon Jul 05 2021

   Areas affected...portions of Montana Wyoming and South Dakota

   Concerning...Severe potential...Watch possible 

   Valid 051834Z - 052030Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Isolated strong/severe storms will likely develop in
   response to warm advection near a frontal zone across the High
   Plains early this afternoon. Isolated instances of hail and damaging
   winds will be possible. A better organized severe threat will likely
   evolve across western portions of South Dakota this evening. A
   weather watch is possible but uncertain in the short term.

   DISCUSSION...Early afternoon water vapor imagery showed a weak vort
   max traversing the central Rockies across portions of western
   Wyoming. Ahead of this feature, several other weak disturbances
   evident in lower-level imagery were crossing the Dakotas and High
   Plains, where remnant morning convection and additional
   boundary-layer cumulus have become more numerous in the past half
   hour. Likely related to weak warm advection/forcing for ascent along
   a diffuse frontal zone, this convection and additional storms should
   track southeastward across South Dakota along the instability axis
   (1500-2500 J/kg MUCAPE). On the fringes of stronger mid-level flow
   aloft, vertical shear less than 30 kts should favor modestly
   organized multicellar clusters. Likely rooted above the surface
   given considerable MLCINH remaining on SPC mesoanalysis, these
   storms/clusters will present mainly a risk for large hail initially,
   before gradually becoming more surface based this afternoon/evening.


   To the west northwest across portions of eastern Wyoming and the
   Black Hills, boundary-layer cumulus was noted developing in a weak
   upslope flow regime. As lift from the approaching trough and
   orographic forcing continue to reduce inhibition, additional storms
   should develop later this afternoon. With 1000-2000 J/kg of MLCAPE
   and enhanced vertical shear around 30-35 kts ahead of the wave,
   organized multicell clusters and perhaps a few supercells appear
   likely to evolve. Damaging wind gusts and hail will be likely with
   the strongest storms as they track to the east southeast into this
   evening. Some upscale growth into one or more small MCS with a risk
   of damaging winds into the overnight hours also appears probable.

   Uncertainty remains high on the threat through the short term with
   trends suggesting the potential for organized severe weather
   remaining quite limited. The need for a weather watch appears more
   likely later in the day for more robust convection developing to the
   west. As such, convective trends will be monitored or a possible
   weather watch this afternoon, though the need for a watch in the
   short term remains uncertain.

   ..Lyons/Guyer.. 07/05/2021

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

   ATTN...WFO...FSD...ABR...LBF...UNR...CYS...BYZ...

   LAT...LON   45780418 45940374 45920304 45360141 44960038 44559938
               44019834 43749814 43349814 43079844 43039914 43029966
               42990029 42960140 43060371 43100429 43630466 44630464
               45260450 45780418