711 ACUS11 KWNS 290045 SWOMCD SPC MCD 290044 NEZ000-SDZ000-290315- Mesoscale Discussion 1370 NWS Storm Prediction Center Norman OK 0744 PM CDT Sun Jun 28 2026 Areas affected...parts pf northwestern Nebraska into southwestern South Dakota Concerning...Severe potential...Watch possible Valid 290044Z - 290315Z Probability of Watch Issuance...60 percent SUMMARY...Increasing strong thunderstorm development appears probable by late evening, if not earlier. This may, at least initially, include evolving supercells with large hail and at least some potential for tornadoes. Although timing remains a bit uncertain, it is appearing more probable that a severe weather watch will be needed at some point this evening. DISCUSSION...Within larger-scale mid/upper troughing across the West, another significant short wave trough is now turning eastward through the eastern Great Basin and will continue to gradually pivot east-northeastward through this evening. This may be preceded by one or two much more subtle perturbations within downstream cyclonic flow across the Colorado Rockies toward the Black Hills vicinity, with at least attempts at isolated thunderstorm development now underway northwest of Mullen NE. This storm appears to be developing near the leading edge of westerly low-level moisture return toward the high plains between the Cheyenne Ridge and Black Hills vicinity, where forcing for ascent associated with strengthening warm advection centered around the 700 mb level is forecast to focus by 02-04Z. Coupled with strengthening deep-layer and low-level shear near the nose of an intensifying low-level jet (50-60+ kt around 850 mb), the potential for supercell thunderstorm development seems likely to increase through mid to late evening, aided by inflow of air characterized by increasingly sizable potential instability. ..Kerr/Thompson.. 06/29/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...ABR...LBF...UNR...CYS... LAT...LON 43240344 44120131 42620001 42340153 41810252 41820354 43240344 MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN