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962 FXUS63 KFSD 112317 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 617 PM CDT Wed Jun 11 2025 .KEY MESSAGES... - Scattered thunderstorms expected to redevelop closer to sunset near I-90 and drift northward overnight. Locally heavy rain and small hail possible. - More showers and thunderstorm are expected throughout the day on Thursday with the potential for strong to severe storms during the afternoon to evening hours. The primary risks will large hail up to (up to 1.5") and strong winds between 60-70 mph. - Locally heavy rainfall is expected with tonight's and Thursday night's developing activity. Accumulations between 0.25" to 0.75" of an inch of rainfall is expected along and north of I-90 through Friday morning with isolated pockets of up to 1.5 inches possible across southwestern MN. - Temperatures rise through the upcoming weekend, bringing additional thunderstorm risks by Sunday and into next week. Monitor for strong storm potential.&& .DISCUSSION... Issued at 340 PM CDT Wed Jun 11 2025 CURRENTS & TONIGHT: Another warm day continues! Taking a look across the area, a line of showers and thunderstorms has developed roughly along a Tyndall to Sioux Falls to Marshall, MN line this afternoon mostly in response to portions of a mid-level shortwave intersecting a 850-925 mb surface boundary. As this developing line of showers and thunderstorms continues to push eastwards into areas east of I- 29 over the next few hours, the presence of a weak LLJ will lead to occasionally strong wind gusts up to 60 mph along with pockets of locally heavy rain in the outlined areas. With this in mind, quick accumulations up to 0.25" of an inch will possible mainly along the MN/IA line ahead of this line. From here, we'll likely see this line exit our area closer to 3 pm as the aforementioned surface boundary continues to push southwards towards the U.S. Highway-20 corridor this evening. With a mostly undisturbed environment (1000-1500 J/kg MLCAPE and 25-35 kts of bulk shear) south of U.S. Highway-18 and dew points in the 60s, could see additional strong to severe storms develop along portions of the Missouri River Valley and the Highway- 20 corridor this evening. With mid-level lapse rates close to 6.5 degrees C/km and "inverted V" characteristics in the soundings at KSUX, any developing semi- discrete cells could produce large hail up to Ping-Pong balls (1.5") and damaging wind gusts up to 70 mph as they merge into multi- cellular clusters. As these storms continue to develop, expect this activity to follow the 850 mb front northwards between 6 pm to 10 pm and gradually weaken as they encounter a more stable environment along and north of I-90. From here, we'll likely see scattered showers with isolated thunderstorms persist across areas north of I- 90 overnight with the focus shifting towards locally heavy rainfall. With warm cloud depths of 10kft, slower storm motions, and mean wind vectors parallel to the surface boundary; lingering showers and thunderstorms could produce efficient rainfall rates between 0.10" to 0.25" of an inch at times according to the HREF with the highest accumulations expected across southwestern MN. With this in mind, could see some localized ponding on roadways and localized flash flooding in urban/low lying areas. THURSDAY-FRIDAY: Heading into Thursday, the severe risk and heavy rainfall threats will be highly dependent on where the retrograding surface boundary end up after tonight. However, similar to the previous package; it does seem like 11.12z guidance has things developing north of I-90 with a focus being along and north of the U.S Highway-14 corridor as another mid-level wave intersects the surface boundary. With this in mind, expect scattered showers with isolated thunderstorms to persist for much of the morning hours as a strengthening LLJ parallels the 850 mb front along and north of I- 90. The risk for strong to severe storms will increase from the early afternoon to the evening (between 3pm to 11 pm) as the surface boundary lifts retrogrades northwards and intersects an approaching mid-level wave in the warm air advection (WAA) wing. With about 800- 1200 J/kg of instability and 35-45 kts of bulk shear to work with, a few developing semi-discrete cells could become severe mainly north of I-90 with large hail being the primary threat as mid-level lapse rates approach 6.5 degrees C/kg. Similar to today, locally heavy rainfall with developing storms will also be a threat especially in the areas that received the most rainfall overnight. Rainfall amounts could vary between 0.25 to 0.75 of an inch with pockets of up to 1.5 inches into Friday. From here, expected showers and thunderstorms to gradually come to an end during the morning hours of Friday as most of the activity pushes east of the area. SATURDAY ONWARDS: Heading into the extended period, an upper-level ridge will slide eastwards into northern plains and flattens into the early part of next week, with at least one more weak wave "riding the ridge" by Sunday. A more defined mid/upper level trough develops by Tuesday and slides into the northern plains. Models continue to diverge in terms of the details with this trough and associated surface low, but this could bring additional shower and storm chances to the region. Although details are uncertain, this pattern is conducive to periods of showers and thunderstorms through the midweek. Machine learning and other guidance indicates that some strong to severe storm potential exists. Lastly, temperatures will continue to sit in the mid 70s to mid 80s for highs through Tuesday. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 610 PM CDT Wed Jun 11 2025 Scattered showers and thunderstorms continue over northwest Iowa early this evening. Eventually, an west to east line of elevated thunderstorms will form somewhere in the vicinity of I-90 and slowly drift north and east through the night. VFR conditions are likely, but temporary drops to MVFR or IFR visibility in heavy rain is possible. Eventually a wave moves east of out western SODAK and begins to push convection north of Highway 14 after daybreak. MVFR to IFR ceilings may try to form along and south of this retreating band of thunderstorms and may linger into the day. More uncertainty to the south where skies may clear and temperatures rise enough to warrant mid-afternoon thunder risks in central South Dakota and the Buffalo Ridge areas. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...05 AVIATION...Dux/05