ZCZC SPCSWOMCD ALL ACUS11 KWNS 051834 SPC MCD 051834 SDZ000-NEZ000-MTZ000-WYZ000-052030- 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 NNNN