


Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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600 FXUS63 KUNR 091828 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1228 PM MDT Wed Jul 9 2025 .KEY MESSAGES... - Scattered to numerous severe storms capable of damaging winds and large hail are anticipated today, especially east of the Black Hills. - Additional rounds of storms, some of which could be strong to severe, are expected tomorrow. - Turning milder and drier on Friday before warm temperatures return over the weekend. && .DISCUSSION...(This Evening Through Wednesday) Issued at 1228 PM MDT Wed Jul 9 2025 Water vapor imagery this afternoon shows a distinct shortwave trof crossing the northern Rockies/High Plains, which supported brief convective initiation over the Bighorns and attempted initiation over the southern Black Hills. Meanwhile, monsoon moisture is advecting northward over the Four Corners toward the central Rockies/High Plains in concert with this wave. Trailing the initial wave, an additional shortwave/vorticity maximum is evident near the Great Basin, also shifting eastward in predominantly zonal flow aloft. Around the area, a juicy boundary layer is in place from south central SD northwestward to the MT/ND border, extending into far northeastern WY, where temperatures in the upper 80s/lower 90s are present with dew points in the 60s to lower 70s. Farther west, a drier/warmer boundary layer is in place, with dew points in the 40s across much of northeastern WY and the Black Hills. A deep, dry elevated mixed layer is being sampled by the 18z UNR RAOB, with dry adiabatic lapse rates from around 850 mb to 500 mb. Skies are mostly clear outside of minimal cloud cover near/ahead of the approaching wave. Aforementioned distinct shortwave trof approaching the area from the west should support convective initiation from west to east over the next 1-3 hours. SPC mesoanalysis fields suggest increasing MLCAPE from west to east, with maxima in the 2000-3000 J/kg range over our eastern/northeastern tier. Deep-layer shear generally ranges from 25- 35 kt, which is sufficient for multicellular and transiently supercellular convection. CAPE in the hail growth zone exceeds 1000 J/kg over portions of northwestern/central SD. Coupled with midlevel lapse rates of 8-9 C/km, the thermodynamic environment is supportive of large/significant hail, especially with any supercells that emerge. Extreme DCAPE values (1500-2000 J/kg) suggest a severe to significantly severe wind risk also exists, particularly with higher- precipitation supercells or any convection that evolves into an MCS/QLCS mode. Environment and CAM solutions combined suggest the most likely corridor for this would be across eastern portions of our area, from the west central to central/south central SD plains. Storms will shift eastward rather quickly with the wave, diminishing from west to east by around 03z. Beyond the initial wave this afternoon/evening, a brief period of shortwave ridging/deep Q-vector divergence may bring an end to convection late overnight/early morning Thursday. However, a trailing shortwave/low-level trof paired with Q-vector convergence aloft will likely initiate additional convection tomorrow morning into the afternoon. Given the strength of forcing, convection may be widespread, but the environment continues to look fairly marginal for severe weather across our area. SBCAPE and 0-6 km bulk shear magnitudes range from 500 to around 2000 J/kg and 10 to 20 kt from west to east, respectively, suggesting that strong but disorganized updrafts may be the predominant mode. However, a more consequential severe threat may emerge with any more organized convection along merging outflow boundaries and/or corridors of locally enhanced shear. Surface trof/front crosses the area late Thursday night into Friday. Associated pressure rises and cold air advection could support breezy northwest winds as drier air spills into the region. Lingering low-level/midlevel moisture could certainly support areas of showers. Limited buoyancy will generally preclude much of a thunderstorm threat, especially strong/severe storms. However, a few storms cannot be ruled out, mainly across south central SD. Guidance has trended towards swinging another shortwave/lobe of Q-vector convergence through the region on Saturday, but a relatively dry post-frontal air mass may limit potential for any impacts to sensible weather across the region. Otherwise, ridging builds into the weekend, bringing a return of warmer and mostly dry conditions. && .AVIATION...(For the 18Z TAFS Through 18Z Thursday) Issued At 1126 AM MDT Wed Jul 9 2025 Generally VFR conditions are expected through the TAF period. Isolated to scattered storms are expected this afternoon and evening. Brief MVFR conditions may be possible in storms. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Sherburn AVIATION...Dye