textproduct: Sioux Falls

KEY MESSAGES

- Continued unsettled conditions remain in the region through the week. No widespread severe weather risks, but conditional and highly localized risks will be possible.

- Focus areas for the majority of the severe weather risks ahead will be west of I- 29 and especially along or west of the James River valley.

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

UPDATE

Issued at 912 PM CDT Mon Jun 1 2026

A few weak showers and isolated weak thunderstorms have developed across northwest Iowa this evening. These showers and storms have developed on a westward retrograding boundary. Think that any additional development will come to an end soon as the boundary layer stabilizes, shutting off the ability for surface based parcels to be lifted to their LFC's. Showers and storms have already developed this evening along the high plains across western Nebraska and western Kansas. This convection is expected to push eastwards through the rest of the evening and overnight timeframe, paralleling I-80. Elevated instability will be much weaker across our area, so any precipitation that does make it into parts of the Missouri River Valley is expected to be mainly rain with perhaps a stray rumble of thunder possible.

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 /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 637 PM CDT Mon Jun 1 2026

Latest satellite imagery shows a small boundary to the east/northeast of KSUX that has produced a few weak showers. Think this boundary will remain east of KSUX long enough that nocturnal stabilization will shut off any additional shower chances. Another round of showers and some thunderstorms looks to weaken near and south/southwest of highway-20 late this evening and night. Will monitor this potential as it encroaches towards the area.

Another round of showers and some storms are possible late tomorrow through the afternoon hours. Too much uncertainty remains regarding the specific timing and location of these showers and storms so have left out of all TAFs at this time. Winds will turn from north/northeasterly this evening to out of the southeast by tomorrow afternoon. The southeast winds will gust up to 20-30 knots to end the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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