textproduct: Sioux Falls

KEY MESSAGES

- Unsettled conditions remain in the region through the week. Spotty showers and non-severe storms are possible west of I-29 this afternoon, with a low confidence risk of strong winds toward central South Dakota after midnight tonight. - Portions of southeast South Dakota will see a Level 2 of 5 risk for severe storms Wednesday evening and Thursday night, with lesser risks farther east and south. Large hail and damaging winds are the primary threats during these periods.

- Temperatures remain in the 80s through the week and rise towards the upper 80s by the end of the weekend.

UPDATE

Issued at 544 AM CDT Tue Jun 2 2026

A mild start to the day with temperatures largely in the mid to upper 60s as of 5 AM. Not many changes to the forecast for today and tonight, which is discussed in detail in the earlier update below.

Severe risks for late Wednesday and Thursday night have expanded eastward, with a Level 2 of 5 risk for portions of southeast South Dakota in each period. For Wednesday, the greater risk is northwest of Lake Andes to Madison to Brookings South Dakota. As alluded to below, the main concern late Wednesday is the potential for a scattered line of thunderstorms developing from central South Dakota to eastern North Dakota mid-late afternoon. Developing storms could quickly become severe, bringing a risk of large hail to 2 inches or larger, along with damaging wind gusts to 70 mph into the middle James River Valley by early evening. CAMs vary in storm coverage, but are showing decent consensus in the location/timing of potential development in central SD 20-22Z with activity advancing into our far western counties 22Z-00Z (5pm-7pm Wednesday). Storms progress east and southeast during the evening, becoming less organized and weakening as they move into southwest MN and far southeast SD as we approach midnight.

Thursday's evolution is lower confidence, and if we can clear early enough to allow destabilization, cannot rule out isolated storms along a lingering boundary in the late afternoon/evening. Main focus is on development across western South Dakota in the afternoon, would could evolve into a line and track east into eastern SD overnight. While some hail would be possible, the primary threat in this scenario is scattered damaging wind gusts before the line moves into a less favorable environment and weakens.

Issued at 912 PM CDT Mon Jun 1 2026

High pressure sitting over the Great Lakes area will be advecting drier, more stable area into the area as east/southeast flow persists through the day tomorrow. This will push the instability gradient to the west. This gradient looks to end up paralleling I-29 by the late afternoon hours tomorrow. A mesoscale convective vortex (MCV) looks to develop from the overnights storms. This MCV looks to interact with this instability gradient and develop additional showers and thunderstorms. Mean flow is roughly parallel to the boundary which looks to allow these showers and storms to persist from late morning through the bulk of the afternoon timeframe. Don't think any of these storms will be strong to severe as deep layer shear is quite weak, on the order of 10-15 knots. However, brief gusty winds, brief heavy rain, and small hail are possible. The main impact from these showers and storms is that the look to either parallel I-29 or develop just to the west of the interstate. Even though these storms are not expected to be strong to severe, they can still impact outdoor events. A MCS looks to develop along the Black Hills and push northeastwards along a surface boundary draped from northeast South Dakota down into the Black Hills. This boundary looks to reside within a surface trough and is somewhat supported by convergence in the low levels. As the MCS progresses northeastwards along the boundary, it looks to run into a worsening environment as instability wanes and shear weakens. This still looks to support a lower end severe weather threat along and west of a Lake Andes, South Dakota to Huron, South Dakota line where large hail and damaging winds are possible before the MCS races out of the available instability and weakens.

Another potential for strong to severe storms is possible on Wednesday. Wednesday is starting to look more like a line of storms as another boundary draped within a surface trough pushes into the area. Shear profiles look to be parallel to the boundary, supporting the potential for a line of storms. That said, still enough uncertainty to not say much beyond that as Tuesday night's storms could affect Wednesday's storms.

DISCUSSION

Issued at 112 PM CDT Mon Jun 1 2026

THIS AFTERNOON/EVENING: Rather stable conditions across the region early this afternoon, outside of a lone elevated storm over north central Iowa. Satellite shows a weak mid-lvl wave crossing central Nebraska and lifting towards the Tri-State area. Soundings closer to home show a very stable layer that should prevent any surface based convection to develop as temperatures rise towards the 80s. What this wave may do is briefly slow the rise in temperatures, but bring a chance for a few high based sprinkles. A second area we'll be monitoring today is right along the eastward edge of the CWA where a bit less inhibition is in place. With a very weak shear profile, any storm that develops is not expected to be strong to severe.

TONIGHT: Most of the focus during the overnight hours will be across the Nebraska Panhandle, Black Hills region, and western Kansas. As yet another wave ejects out of the central Rockies, we should see renewed convection develop and quickly try to congeal into one or more clusters as they cross western Nebraska and South Dakota. Latest CAMS continue to hint at these storms trying to slowly lift northeast but should weaken as they reach a more stable atmosphere. That said, Could continue to see a limited wind risk into south central South Dakota and along portions of the Missouri River valley by 3am. Further north, the abundance of low-lvl moisture combined with light winds could lead to patchy fog developing.

TUESDAY: We'll have to keep a close eye on the progression of the convection in Nebraska as guidance does show signs of a developing MCV that may track east and slowly north during the day. At this point, destabilization of the boundary layer will need to be watched as we could see pockets of 2000 J/KG MLCAPE develop in a narrow corridor ahead of this wave. Isolated to scattered storms could develop based on the weakening of convective inhibition somewhere between the James river and I-29. Effective shear remains very weak. but there may still be appreciable 0-1km helicity to lead to a few rotating storms/funnels. However the widespread severe risk remains low and more focused on marginal hail, but could see future outlooks extended further east. Better focus for convection will be across far western SD along a frontal boundary edging into the state. As yet another wave ejects into the Plains scattered convection along this boundary should develop and begin to track east northeast. One thing to note today is that mid-lvl heights may be rising across central SD in the evening, with 700 mb temperatures also rising. The more meridional 700:500 flow should prevent a strong eastward shift after dark.

WEDNESDAY/THURSDAY: Uncertainty grows with the Wednesday and Thursday forecast as we remain stuck in this general mid-lvl southwesterly flow pattern. The aforementioned front will attempt to slide eastward on Wednesday, though a much more e complicated forecast in regards to the environment ahead of the front. Yet another weak mid-lvl area of vorticity tracks through the Tri-State area, increasing the risks for mid-lvl clouds but also a few showers and isolated thunderstorms by the afternoon. The area with the greatest risks for strong convection will be along that frontal boundary in central South Dakota by mid-late afternoon. Additional showers and thunderstorms may be possible into the overnight hours further east as the LLJ intensifies. Latest NBM guidance suggests 8- 95% PoPs in this timeframe, but my confidence in overall coverage is not as high as that chance suggests. A bit of a repeat performance on Thursday, with the greatest severe risks again focused west of the James River and into Southwestern South Dakota by the afternoon.

FRIDAY-SUNDAY: MId-lvl troughing moves through the Dakotas on Friday, potentially pushing strong convective risks further east into MN/IA. Confidence is very low in this time period given all of the various uncertainty associated with the forecast in the days before. Confidence rises for next weekend with drier weather and near to slightly above normal temperatures likely.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 636 AM CDT Tue Jun 2 2026

VFR conditions are expected through the period. Scattered showers and thunderstorms are expected to develop after 16Z-18Z. This activity will be mainly west of I-29, but could impact KHON in the mid-late afternoon. Southeast winds become a bit breezy with occasional gusts 20-25kt during the afternoon through sunset.

Lower chances for storms moving in from the west late tonight. This would again mainly impact KHON TAF site, but given low confidence, did not include any mention of TSRA after 03/06Z.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.