750 FXUS63 KUNR 020355 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 955 PM MDT Sun Jun 1 2025 .KEY MESSAGES... - There is a marginal (level 1 of 5) risk over portions of northeastern WY this afternoon and evening. Main threats will be large hail and damaging winds. - There is a marginal (level 1 of 5) to slight (level 2 of 5) risk over south central SD for Monday afternoon and evening. Main threats will be large hail and damaging winds. - Unsettled weather continues through next week with daily chances for showers and storms. && .DISCUSSION...(This Evening Through Sunday) Issued at 155 PM MDT Sun Jun 1 2025 WV imagery depicts upper level ridge over the Northern Plains with a deepening trough over western Canada/the PNW. Sfc analysis shows the a sfc front/trough draped across southeastern MT. 18z KUNR sounding depicts 1300 J/kg SB CAPE within a strongly capped and dry environment. Visible satellite imagery shows clear skies over the CWA with clouds/convection beginning to form off of the Big Horns. The instability and increasing shear will contribute to a marginal (level 1 of 5) severe threat over northeastern WY late this afternoon and evening. However, with the lack of moisture and main source of lift coming through after dark, confidence in severe weather occurring this afternoon and evening remains very low. Most recent CAMs show a line of convection developing by 02-03z with a few isolated storms forming ahead of the line. If strong to severe storms manage to form, the main threats will be hail (1+" diameter) and damaging winds (60+ mph gusts). The main cold front will push through the CWA overnight and will have mostly passed through the CWA by Monday afternoon. Therefore, while we may see a few thunderstorms in the morning with the sfc cold front and then later in the afternoon as the upper level front moves through, it`s unlikely we`ll see anything too widespread or severe for much of the CWA. However, further east towards south central SD, the front will be moving through during the afternoon hours. There`s a marginal (level 1 of 5) to slight (level 2 of 5) severe risk across portions of far south central SD and along the SD/NE border as moderate instability (MU CAPE of 1000-1500 J/kg per NAM) develops ahead of the front. The strongest shear remains displaced from the best instability, so a widespread severe threat isn`t anticipated at this time. Stronger storms will be capable of hail (1+" diameter) and damaging winds (60+ mph gusts). Northwest winds will also pick up Monday behind the front, supported by 3 hr pressure rises of 2-4 mb, 30-40 kt 850-700 mb winds, and modest CAA. HREF guidance has been conservative on wind probs with low (0-20%) chances for gusts to exceed 45 mph. The NBM does have medium (40-60%) probs for 45 mph gusts, mainly over the western SD south of I-90 on Monday afternoon and evening. Therefore, will not issue any headlines. As we enter the mid-to-late week, quasi-zonal and active flow develops over the central US. In terms of sensible weather impacts it will mean moderating temperatures (highs will be in the 60s to 70s) with periodic chances for showers and storms. && .AVIATION...(For the 06Z TAFS Through 06Z Monday Night) Issued At 955 PM MDT Sun Jun 1 2025 Scattered storms will continue across northeastern WY and western SD tonight and again on Monday, as a cold front crosses the region. MVFR CIGS will move into NE WY late tonight, then western SD on Monday behind the front. IFR conditions will be possible across the higher Black Hills. Gusty NW/N winds are also expected late tonight and Monday. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Wong AVIATION...13