ZCZC SPCSWOMCD ALL ACUS11 KWNS 192158 SPC MCD 192158 SDZ000-NEZ000-NDZ000-MTZ000-WYZ000-192330- Mesoscale Discussion 1017 NWS Storm Prediction Center Norman OK 0458 PM CDT Sat Jun 19 2021 Areas affected...Southeastern Montana...northeast Wyoming...and portions of the Dakotas. Concerning...Severe potential...Watch unlikely Valid 192158Z - 192330Z Probability of Watch Issuance...20 percent SUMMARY...Storm initiation appears possible in the next 1 to 2 hours across the central and northern High Plains. A narrow corridor of buoyancy will support a few hours of isolated severe potential with high-based storms. Uncertainty on storm coverage and severity remains high. DISCUSSION...Ahead of a deepening mid-level trough observed on afternoon water vapor imagery, towering cumulus has become progressively more agitated from far southeastern Montana into northeastern Wyoming. Incipient updrafts along the crest of the Big Horns and higher terrain in southeast Montana suggests the airmass across the High Plains is likely nearing minimal convective inhibition. SPC mesoanalysis indicates between 500-1500 J/kg of MLCAPE have developed in a narrow corridor from the Nebraska Panhandle northward, owing to steep mid-level lapse rates and surface mixing ratios between 8 and 10 g/kg. Weak upslope flow, diurnal heating, and background ascent from the approaching mid-level wave should further diminish remaining inhibition, and may allow for convective development in the next couple of hours. CAM guidance remains unreliable in the weak ascent regime, but does hint at one or more clusters of storms evolving off the higher terrain this evening. The primary severe threats will be damaging outflow winds and hail, given moderate buoyancy and steep low/mid-level lapse rates. Across the Black Hills of western South Dakota, cloud debris from earlier convection is inhibiting strong surface heating casting doubt on storm initiation in this region. Here, deeper surface moisture and higher buoyancy may support a locally greater, but more conditional severe threat for wind and hail into this evening. Given the narrow corridor of destabilization and the uncertainty on storm coverage/intensity, a weather watch is unlikely, though trends will be monitored. ..Lyons/Guyer.. 06/19/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BIS...LBF...UNR...CYS...BYZ...GGW... LAT...LON 42540325 42570417 43430464 44650494 45680493 46490480 46640474 46820434 46590388 45590312 44680263 43960228 43370213 42610256 42540325 NNNN