


Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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921 FXUS63 KUNR 141713 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1113 AM MDT Sat Jun 14 2025 .KEY MESSAGES... -Daily chances for thunderstorms, some possibly severe, through Monday -Fog again in the Plains and foothills Sunday morning -Wet and cooler mid-week, followed by mostly dry and warmer weather && .UPDATE... Issued at 954 AM MDT Sat Jun 14 2025 The synoptic-scale pattern has changed little from yesterday. Moist southeasterly lower tropospheric flow coupled with the diurnal minimum once again resulted in fog and low stratus across the Plains, up to the foothills this morning. This is eroding a little quicker than was the case yesterday. Early thoughts on convective potential later today based on observational data and new models allows us to offer a little more clarity now, and we will continue to refine the forecast throughout the day. Current thinking is that the capping EML is a negative for convective initiation over the Black Hills, though the chances are higher than yesterday given higher magnitude of surface diabatic heating and a more pronounced upper level perturbation seen in 6.3- micron water vapor imagery upstream. This wave has minimal effect at lifting the capping EML though, per model forecast soundings, but could be just enough. If convection does develop, hodographs look to favor splits, with initial cloud-bearing wind carrying cells eastward at around 15-20 mph, but left splits/anticyclonic mesos deviating north-northeastward and right movers/cyclonic meso slowing slightly and deviating south-southeastward. Some terrain-driven variance in the wind field could shift this storm-scale behavior some. The primary impetus for convection is expected to be the Bighorns and Laramie mountains again, where elevated heating will be the strongest. As convection moves eastward it will almost immediately enter a more unstable regime causing convective intensity to increase by mid-afternoon. Although midlevel flow is still quite weak, lower tropospheric directional shear is enough for supercells. Similar motion and behavior to yesterday is expected with cellular convection tending to split and move fairly slow with primarily a large (potentially very large, 2+") hail threat, while any cold pool-driven convection propagates eastward and transitions to primarily a wind threat. Forecast challenge for today will be to refine footprint of convective coverage. The best chance for the foothills and Plains to receive precipitation today will be if cold pool driven upscale growth of clusters or an MCS happens, and probably fairly late in the day. We will likely need to refine timing and precipitation probabilities as we see this start to evolve. && .DISCUSSION...(Today Through Friday) Issued at 315 AM MDT Sat Jun 14 2025 Upper air analysis shows weak ridging across the central/northern Plains. SW flow persists across the central/northern Rockies ahead of a stalled Pac NW upper low. This active flow continues across the western CONUS as several shortwaves cross the northern Plains. KUDX radar shows a weakening MCS across NW SD continuing eastward. Also, lingering showers across south central SD over Todd/Tripp counties will soon be departing the CWA. Low clouds/areas of fog are again expected early this morning but shouldn`t be as widespread as yesterday. Warm/moist airmass will persist across the area, with dewpoints in the low to mid 60s. Highs will reach the upper 70s over NW SD to near 90 near the Neb border. The next wave will cross the CWA this afternoon and evening. Convective initiation will take place along the Bighorns/Laramie mountains and move into NE WY in the afternoon. CAMs show storms then enter an axis of stronger instability and minimal CIN centered across the Black Hills. Shear profiles will be strong enough for supercell development, with large hail and damaging winds possible. Then as storms move east off the Black Hills after ~02z through the western SD plains, the threat transitions more to damaging winds. The 06z HRRR is also suggesting a secondary line of storms later in the evening coming off the Bighorns and pushing across NE WY. These storms then reach the Black Hills area closer to 05/06z before weakening. Initially over NE WY, these storms could produce both hail and wind, but appear to be more wind based by late evening as it nears the Black Hills. Confidence is low with this exact solution & intensity of storms, but a couple of other CAMs do suggest some secondary precip over NE WY (though much weaker). With little change to the pattern through Sunday and Monday, both days should be a general repeat of today. Storms develop across NE WY in the afternoon, cross the Black Hills region around 00z, then push east, becoming more wind based through the evening. An exception on Monday is a cold front crossing the CWA during the day will limit the best instability/storms to SW/SCentral SD. Models continue to show a strong wave crossing the region on Tuesday. Cooler temps in the upper 60s/70s are expected with more widespread showers/isolated storms Tue/early Wed. Severe weather is not expected. Generally drier weather is then expected for the second half of next week, with above average temps. && .AVIATION...(For the 18Z TAFS Through 18Z Sunday) Issued At 1113 AM MDT Sat Jun 14 2025 Winds will generally be southeasterly with some variance in and near convection that develops later today. We refined the window for convection slightly in the TAFs for GCC via a TEMPO, holding PROB30 for RAP where uncertainty is highest. Amendments may be needed. If a storm impacts either airport with expect brief visibility reductions and strong wind gusts. Fog is again possible at RAP and all across the Plains Sunday morning. Low probability of IFR or lower, so MVFR for now. Greater chance of convection just after the TAF period late Sunday for RAP. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ UPDATE...Bowers DISCUSSION/KEY MESSAGES...13 AVIATION...Bowers