ZCZC SPCSWOMCD ALL ACUS11 KWNS 172045 SPC MCD 172045 SDZ000-NEZ000-MTZ000-WYZ000-172215- Mesoscale Discussion 1306 NWS Storm Prediction Center Norman OK 0345 PM CDT Mon Jun 17 2024 Areas affected...portions of eastern Wyoming...southeastern Montana and far western South Dakota Concerning...Severe potential...Watch possible Valid 172045Z - 172215Z Probability of Watch Issuance...60 percent SUMMARY...Thunderstorms are expected to develop off the Bighorns and higher terrain later this afternoon. A few supercells may evolve with a risk for large hail and damaging winds. There remains some uncertainty on the southern and eastern extent of the severe risk, but a WW is being considered. DISCUSSION...Across portions of central and northeastern WY, afternoon visible imagery showed increasing vertical development of cumulus near the Bighorn Mountains and higher terrain. Over the last several hours, diurnal heating and upslope flow have increased ahead of an approaching upper trough and a deepening surface low over south-central WY. As forcing for ascent increases, remaining inhibition will quickly be removed supporting thunderstorm development this afternoon. Confidence in convective development remains highest across north-central WY near the Bighorns where low-level upslope flow is maximized beneath the coldest mid-level temperatures. However, strong low-level mass response is occurring ahead of the deepening surface low over southeastern WY which could support an isolated storm or two farther south. While low-level moisture is not overly deep or rich, low 50s F surface dewpoints have surged westward into eastern WY and portions of southern MT. With 500-1000 J/kg of MLCAPE in place, a few stronger updrafts are likely to evolve as the initial convection moves off of the higher terrain. There remains some uncertainty on the eastward extent of destabilization given lingering cloud cover, though clearing is ongoing. Strong flow aloft ahead of the upper trough is supporting robust vertical shear profiles with relatively long hodographs and 50+ kt of effective shear. More than sufficient to support organized rotating updrafts, these storms will likely be capable of large hail and damaging gusts. A brief tornado can also not be ruled out given some low-level veering and potential for terrain enhanced low-level shear. Given the potential for a few supercells capable of hail and damaging winds, a new WW may be needed in the next 1-2 hours. ..Lyons/Halbert/Gleason.. 06/17/2024 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...UNR...CYS...BYZ...RIW... LAT...LON 42870395 42480400 42290421 42250460 42740553 43680688 44030721 45480711 45890652 46080591 46080526 45960471 45570434 45160407 44710385 44360382 43780390 42870395 NNNN