SPC MD 979

MD 0979 CONCERNING SEVERE POTENTIAL...SEVERE THUNDERSTORM WATCH LIKELY FOR PORTIONS THE SOUTHEASTERN MONTANA INTO THE BLACK HILLS Mesoscale Discussion 0979 NWS Storm Prediction Center Norman OK 0232 PM CDT Thu Jun 04 2026 Areas affected...portions the southeastern Montana into the Black Hills Concerning...Severe potential...Severe Thunderstorm Watch likely Valid 041932Z - 042100Z Probability of Watch Issuance...80 percent SUMMARY...Scattered strong to severe thunderstorms will develop eastward through the afternoon, with large to very large hail and strong/severe wind gusts the main hazards. A Severe Thunderstorm Watch will likely be needed for a portion of the discussion area. DISCUSSION...Moist, southeasterly flow north of a quasi-stationary surface boundary and continued surface heating are contributing to steepening low-level lapse rates and eroding MLCIN across portions of the northern High Plains as of early this afternoon. Coupled with increasing ascent ahead of an approaching mid-level shortwave trough, this is promoting gradual thunderstorm development across southeastern Montana and northeastern Wyoming, with deepening cumulus also noted along portions of the Black Hills. As this activity evolves eastward through the afternoon, two different regimes of severe potential appear likely. In the Black Hills vicinity, western/central South Dakota, and northwestern Nebraska along and north of the surface boundary, modestly strong westerly flow aloft (35-40 kts sampled at 4-5 km AGL by the BLX/RIW VAD profiles) and effective shear of 35-45 kts are likely to overlap greater low-level moisture and moderate buoyancy (MLCAPE around 1000-2000 J/kg), with occasional supercells possible. Coupled with steep mid-level lapse rates (700-500 mb lapse rate of 8.7 C/km sampled by the 18z UNR observed sounding) and elongated hodographs, this should support large to very large hail as the primary threat. Meanwhile, latest guidance and objective analysis depicts marginally weaker effective shear (around 25-35 kts) and steeper low-level lapse rates farther to the north across portions of eastern Montana into southwestern South Dakota. This would favor upscale growth along developing cold pools, with a more multicellular storm mode and greater risk for strong to severe wind gusts. Trends will continue to be monitored, and watch issuance will likely be needed for a portion of the discussion area to cover these threats. ..Chalmers/Mosier.. 06/04/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...BIS...LBF...UNR...CYS...BYZ...GGW... LAT...LON 44050566 44700590 45420596 46080589 46630550 46990469 47200376 47120307 46960267 46600228 46110206 44910200 43990199 43250200 42870201 42590212 42320225 42180243 42150271 42170310 42220361 42500419 43150505 44050566 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN Read more