ACUS11 KWNS 210454 SWOMCD SPC MCD 210454 COZ000-210700- Mesoscale Discussion 1224 NWS Storm Prediction Center Norman OK 1154 PM CDT Sat Jun 20 2026 Areas affected...portions of northeast Colorado Concerning...Severe potential...Watch unlikely Valid 210454Z - 210700Z Probability of Watch Issuance...20 percent SUMMARY...Isolated thunderstorms capable of producing large hail will be possible this evening into the early morning hours. The overall limited space and time of this threat should preclude a watch. The area will continue to be monitored. DISCUSSION...Despite the cool nocturnal boundary layer, isolated supercell thunderstorms have developed across portions of northeast Colorado this evening. These storms are developing on the nose of an objective analyzed 70-knot upper-level jet moving across the central Rockies, and appear to be rooted around 700 millibars per RAP forecast soundings. One of these supercells produced 2.5" hail across portions of Logan County, CO, within the last hour before weakening and eventually dissipating as it moved east. A second supercell has developed to its southwest across Weld County, CO. This secondary supercell appears to have undergone a split, with the left mover remaining nearly stationary over Greeley, CO. Multi-radar, multi-sensor objective analysis of these storms suggests hail around 1.5" is possible. Although there is a lack of well defined low-level forcing mechanisms, general large-scale ascent of a moist unstable environment will support an ongoing threat of thunderstorm development this evening into the early morning hours. Steep lapse rates in the 700-500 millibar layer (around 9 C/km) will support large hail potential with any of these storms, perhaps even significant (2-2.5") hail. The overall space/time of this potential should remain fairly limited and a watch is currently not anticipated. However, should it become apparently that additional thunderstorm development is likely, a watch may be considered late this evening/overnight. ..Marsh/Smith.. 06/21/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...GLD...BOU... LAT...LON 40250504 40810482 40880382 40700274 40700254 40080260 39820297 40000452 40250504 MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN