textproduct: Sioux Falls

KEY MESSAGES

- Severe weather risks increase quickly after 5pm in South Central South Dakota and North Central Nebraska, and will spread east northeast into the early overnight hours.

- A few discrete storms could initially produce 2"+ hail, 70 mph wind gusts, and even a tornado. Eventually, storms may merge into a wind driven line as they move towards MN/IA. Storms exit around 2am.

- Temperatures remain well above normal through the rest of this week and into the upcoming weekend, with highs in the 90s possible by mid-late week.

- The heat and humidity may bring occasional risks for overnight thunderstorms, with some focus around late Wednesday night and again Friday morning. Exact locations of storms remain uncertain.

DISCUSSION

Issued at 111 PM CDT Tue Sep 1 2026

THIS AFTERNOON: A complex convective setup this afternoon as a pair of mid-lvl vorticity centers continue to pivot northeast. One such area continues to push north of Sioux Falls, with a second stronger area of energy now lifting northward through the Nebraska panhandle. The result thus far has been a significantly contaminated warm sector with plenty of mid-upr clouds over the Tri-State region. At the surface, a stationary boundary/warm front currently stretches from the Platte River to north of Omaha and north of Ames. The airmass north of this boundary continues to warm, suggesting some potential for a northward push in this front by evening as deeper synoptic lift arrives, but for the most part this area will remain capped to surface based convection into late afternoon.

LATE AFTERNOON/EVENING/TONIGHT: We'll continue to see MLCAPE values climb upwards through the afternoon, potentially between 2000-3000 J/KG, but how far north with this instability reach is still uncertain. Ongoing elevated convection in NC Nebraska may keep some areas north of I-90 from any significant level of destabilization, with the largest reservoir of CAPE along and especially south of I- 90. Most guidance would favor new convective development along an surface convergence zone in NE Nebraska or SC South Dakota after 5pm in a narrow corridor of deeper instability. Given favorable shear profiles (effective shear 40+ knots), any initial development should have supercellular characteristics capable of 2" hail and 70 mph winds. Additional convection may try to develop over central Nebraska and lift northward to the MO River in the evening. As we move through the mid-late evening hours, 0-1km shear will be on the rise as the LLJ develops, introducing at least the low end potential for a brief tornado south of I-90 if storms can stay discrete. Though boundary layer stabilization will be on the increase and LCLs remain quite high. Otherwise, watch for gradual clustering of storms as they track east northeast into MN/IA which would increase the potential of 70+ mph winds, with a continued very low probability of a QLCS- like tornado into NW Iowa. 17Z SSCRAM-HRRR data would support the rising potential for high winds extending north of Highway 20, with brief hail potential in new updrafts driven by the LLJ further north into western MN. Latest projections continue to push convection east of the CWA by 2am, with light winds and wet ground perhaps allowing patch fog to develop.

WEDNESDAY: Brief shortwave ridging tries to move in early Wednesday as the surface front settles back into eastern Nebraska and north central Iowa. A few lingering elevated showers/thunderstorms may persist into NW Iowa through mid- morning. With a slightly drier easterly wind, temperatures again rise into the middle to upper 80s, with the latest guidance supporting a strong enough EML to prevent convection along the boundary. The return of the nocturnal LLJ Wednesday night could again lead to isolated to scattered elevated convection into Thursday morning.

THURSDAY-FRIDAY: Confidence remains rather high that temperatures continue to rise towards the lower 90s in most locations for the end of the week. Increasing mid-lvl heights through the Plains will help push low-lvl temperatures well above normal, with H850 temps +26C Thursday and Friday. The greatest challenge in the medium range will be timing and tracking one or more weak ridge riders that will cross the Plains into the weekend. Once such wave may drop down from the NW into MInnesota early Friday morning, perhaps leaving an outflow boundary near the Minnesota River/Ridge areas for the afternoon.

SATURDAY-MONDAY: Temperatures remain above normal through the weekend and into early next week as the 500 mb ridge peaks through the central CONUS. One or more weak waves top the ridge during the weekend, creating a very low confidence PoP forecast during the overnight hours. Should one of these waves track close enough to the CWA they could lead to some temperature reductions.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1154 PM CDT Tue Sep 1 2026

Thunderstorms will continue to push eastward for the first couple of hours of the TAF period. So far, visibilities and ceilings have remained VFR even under thunderstorm activity. Thinking that trend should continue through the early overnight hours, with TAFs maintaining VFR. Otherwise, clouds will clear overnight, and winds will remain under 10 knots through the end of the TAF period. There is a very low chance that fog develops late tonight into early Wednesday morning. Therefore, left any mention of fog out of the TAF. Towards the very end of the TAF period late Wednesday evening/early Thursday night, another round of showers and thunderstorms may develop in northeastern Nebraska. This activity will approach KSUX around the end of the TAF period. With uncertainty on timing and coverage, elected to make no mention of TSRA for that period in this set of TAFs. Future TAF iterations can add it in as predictability increases.

FSD WATCHES/WARNINGS/ADVISORIES

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