000 FXUS63 KUNR 021922 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 122 PM MDT Fri Jun 2 2023 .DISCUSSION...(This Evening Through Friday) Issued at 120 PM MDT Fri Jun 2 2023 Our rather quirky upper level pattern continues...High pressure centered over the Upper Midwest/Great Lakes with an upper low over the Inter-mountain West. Water vapor imagery shows multiple shortwave troughs rotating cyclonically around the upper low. Scattered showers and thunderstorms have begun to form across northeastern Wyoming and the Wyoming Black Hills. At the surface, an area of elongated low pressure is roughly centered over eastern CO into eastern WY. A moist airmass is in place with surface dewpoints in the upper 50s to low 60s across the forecast area. This moist airmass was well sampled via regional 12z soundings - precipitable water values from a few locations: UNR: 1.09" (93rd percentile; 161% of normal); ABR: 1.41" (92nd percentile; 172% of normal; and LBF: 1.18" (90th percentile; 146% of normal). While effective bulk shear is weak (< 20-25 knots), increasing forcing for ascent, 500-1500 J/kg of MLCAPE, and little to no convective inhibition will support scattered showers and thunderstorms through the evening hours. Given the weak shear, any severe weather threat will be limited; although small hail and marginally severe wind gusts are possible. Any convection that does form will pose a threat of heavy rain, although any flash flooding threat will be tempered by brisk storm motions (20-30 knots). The axis of heaviest rainfall will stretch from eastern/central Wyoming into Montana, where greatest large-scale ascent is focused. The aforementioned upper high will slowly drift westward, becoming centered over the Northern Plains Saturday into early next week. Although daily chances of showers and storms will persist into early next week, little to no upper level ascent will be in place under the high pressure. Despite the moist airmass, this lack of forcing will result in isolated chances of storms at best by Monday. Better chances of storms will be displaced west of the forecast area, where more focused large-scale ascent will be centered. The threat of widespread severe weather this weekend into next week looks limited given weak mid-level flow and subsequently weak shear (0-6 km bulk shear 10-25 knots). Recent deterministic models and EPS/GEFS/NAEFS are all fairly good agreement that upper ridging returns to the western half of the US by the latter half of next week with continued warm temperatures into next weekend. && .AVIATION...(For the 18Z TAFS Through 18Z Saturday) Issued At 1101 AM MDT Fri Jun 2 2023 Areas of MVFR stratus will gradually dissipate through early afternoon. Scattered showers and thunderstorms are expected again this afternoon and evening with local IFR conditions. Areas of IFR stratus/fog may once again develop late tonight and early Saturday. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION...Eagan AVIATION...Johnson