


Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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725 FXUS63 KUNR 052303 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 503 PM MDT Sat Jul 5 2025 .KEY MESSAGES... - Several rounds of severe thunderstorms possible today through tonight. - Significant winds over portions of far northeastern WY and northwestern and west central SD this evening are the primary concern today into tonight. - Additional strong to severe storms may occur Sunday and Monday. - Deep ridging builds over the region Tuesday and Wednesday, bringing hotter temperatures and lower storm chances. && .DISCUSSION...(This Evening Through Saturday) Issued at 1243 PM MDT Sat Jul 5 2025 Water vapor imagery this afternoon shows modest drying/subsidence over the region ahead of a potent shortwave near the ID/MT border. Despite the subsidence, a few thunderstorms have developed over the central/southern Black Hills this afternoon in a corridor of terrain- enhanced convergence. So far, these storms have been limited in scope and intensity, with subsevere hail and cloud-to-ground lightning the primary hazards. The prospects of these storms are explored more below. Across northwestern SD, a boundary is propagating southeastward away from morning convection that was primarily confined to portions of ND. This boundary is presumably rooted above the surface, as there is little if any reflection of the boundary in surface observations as it crosses the area. Water vapor also indicates some gravity wave-like perturbations emanating southeastward behind this lead boundary. This may be something to watch for convective evolution later in the afternoon/evening, but given how long the environment has to evolve before the main round of convection late this afternoon into tonight, do not see this being a large factor for now. For the rest of today into tonight, we are watching the potential for three rounds of thunderstorms: 1) this afternoon over the Black Hills, 2) late afternoon through the evening over northeastern WY and northwestern/west central SD, and 3) late overnight, with less certain positioning. 1) This afternoon over the Black Hills: The large-scale pattern through mid afternoon continues to favor subsidence over much of the region, which would tend to limit potential for convective initiation and/or strengthening. However, capping over the Black Hills is fairly weak, and upslope flow leading to terrain-driven convergence has already been sufficient to overcome the inversion despite larger-scale subsidence (as noted above). SBCAPE is more than sufficient to support updrafts (1000-1500 J/kg or greater), but deep-layer shear is marginal (<30 kt). As such, severe potential will be relatively limited with any storms that develop. However, some borderline severe hail (~quarter size) cannot be ruled out in the strongest storms. Large-scale downward motion should favor weakening of the storms as they attempt to move off of the Hills/away from the zone of convergence. 2) Late afternoon/evening over northeastern WY through west central SD: This is expected to be the main show. Clusters and/or lines of storms should develop to our west over MT/WY during peak heating ahead of a potent midlevel disturbance. Ahead of these storms, SBCAPE will increase to around 1000 J/kg, while DCAPE climbs to 800- 1200 J/kg. Evening stabilization looks limited ahead of the approaching storms, with 0-3 km CAPE values actually increasing to 50-100 J/kg preceding their arrival. HREF mean 0-6 km bulk shear magnitudes reach 40-50 kt, with much of that shear concentrated in the lowest 3 km or so as low-level hodographs become increasingly elongated. Altogether, this environment should be capable of at least maintaining the arriving clusters/lines of storms, with further strengthening possible. Given mode, severe to significantly severe straight-line winds should be the primary threat; however, the environment will also be suitable of stronger, longer-lived mesovortices within lines that may support brief tornadoes. Embedded rotating updrafts may also produce hail of quarter to ping-pong ball sized or so. 3) Late overnight, particularly around midnight MDT or later, robust warm-air advection atop outflow from the preceding episode of storms may spark a third round of strong to severe storms. As the corridor of severe storms with the second round has shifted southward in guidance, so, too has this subsequent round, consistent with more southward placement of the associated outflow boundary. Latest guidance paints this activity close to the Black Hills/I-90 corridor. The timing, location, and severity of this convection is much more conditional compared to the first two rounds; however, robust MUCAPE and long, looping low-level hodographs could support elevated supercells capable of large hail and even damaging winds. Today`s multiple rounds of convection, their attendant boundaries, and associated environmental modification heading into later tomorrow morning/afternoon will play a large role in evolution of storms and severe potential tomorrow. The most likely corridor of strong to severe storms will be from our far western tier/northeastern WY through far southwestern SD toward south central SD, where outflow is less likely to wash out appreciable buoyancy. With that said, details will still be challenging to pinpoint until sometime tomorrow morning. Longer-term, another shortwave trof crosses the region Monday, which could spark additional strong to severe storms (especially over central SD) before ridging builds into the region Tuesday into Wednesday. Ridging will bring hotter temperatures and lower chances for precipitation, though daily isolated storms cannot be ruled out. && .AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening) Issued At 458 PM MDT Sat Jul 5 2025 Thunderstorms are expected to cross the area this evening. Strong and variable wind gusts are possible, in addition to large hail. Chances for -SHRA/TSRA across the Black Hills area will continue through the overnight hours, then move eastward toward central SD Sunday morning. Otherwise VFR conditions are expected through the period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Sherburn AVIATION...13