textproduct: Sioux Falls

KEY MESSAGES

- Very isolated strong to severe storms are possible through about 1 am tonight mainly along the Highway-14 corridor in southeastern South Dakota. Large hail up to the size of half dollar coins will be the main threat.

- Warm and humid conditions continue this weekend. Afternoon heat indices will approach 100F along portions of the Missouri River Valley Sunday as temperatures climb into the 90s.

- Low chances (<= 25%) for rain will persist through the weekend and Monday. Chances for rain increase up to a 50-80% chance for Tuesday. Severe storms could accompany this chance for rain, so continue to monitor the latest forecast.

- Above normal temperatures and additional chances (20-40%) for rain persist for the rest of next week.

UPDATE

Issued at 920 PM CDT Sat Aug 29 2026

Strong to severe thunderstorms have developed over north-central South Dakota early this evening and are moving very slowly east-southeastward. Though there is ample effective shear nearing 50 kts, increasing CIN should help weaken the storms before they arrive along our Highway-14 counties. Still, given the shear values, hail up to the size of half dollar coins can't entirely be ruled out in the strongest storms along the Highway-14 corridor of southeastern South Dakota starting around 10:30-11 pm. Any severe threat should come to an end rather quickly, likely ending by 1 am.

Additional showers and storms may develop to our south of parts of Nebraska late tonight/early tomorrow morning where the strongest low level jet will be located, with the northern edge of this LLJ creeping into northwest Iowa. Most of this activity likely stays south of the area, but can't rule out some showers and non-severe thunderstorms developing mainly along the Highway 20 corridor of northwest Iowa between 2 am and 7 am Sunday.

A very warm Sunday is in store for the area, with the heat index potentially reaching the triple digits at times in parts of the area. Still looking like coverage of these 100 degree heat indices will be fairly low and patchy, but will assess the full suite of 00Z guidance before making any heat headline determination.

DISCUSSION

Issued at 229 PM CDT Sat Aug 29 2026

Clearing skies and warm temperatures have returned to the area this afternoon. Temperatures will warm a little bit more to the 80s to low 90s with heat indices up to the upper 80s and 90s. A few locations along the Missouri River Valley are expected to see heat indices touch 100F this afternoon before temperatures cool as the sun begins to set. A few light showers/sprinkles persist across parts of southwest Minnesota but will push east of the area over the next hour or two. Attention then turns to the evening timeframe where additional chances for rain look to return to the area. Showers and some storms look to develop across western Nebraska and southwest South Dakota. These showers will push eastwards into an increasingly stable airmass sitting over the forecast area. At the same time, vertical shear values will be weakening as well. Still, can't rule out the potential for an isolated strong storm or two between 9pm to 3am. Should a strong storm or two develop, it could produce large hail up to the size of a quarter (1 inch) and damaging winds to 60 mph IF the storm can tap into the boundary layer. The most likely location to see these potentially stronger storms is along and west of the James River. Elevated showers look to persist through the rest of the night.

Sunday will be a similar day with high temperatures once again expected to warm to the upper 80s and 90s. This will again push heat indices to the 90s with a few locations along the Missouri River again seeing heat indices touch 100F during the afternoon timeframe. A stronger shortwave trough will be passing mainly through Montana throughout the day. This wave however will take on a negative tilt and push into northeastern Montana and northwestern North Dakota. Severe storms are possible in this area but is much more questionable for our area. Especially as the cold front tied to this wave pushes into the forecast area due to limited moisture/instability and capping just ahead of the front. Thus, have left PoPs dry for Sunday evening and night.

The cold front will push through the area Sunday night through Monday morning. With the front just south of the area, Monday looks to be a continuation of warm and dry conditions with highs warming to the 80s to up to about 90F. Chances for rain look to return to the forecast on Tuesday as a weak shortwave trough pushes into the Northern Plains. The mass response from this wave will return the previously mentioned boundary northwards as a warm front. The ensembles generally show a 50-80% chance for rainfall totals to exceed a tenth of an inch. This will likely be contingent on where the front sets up and if the cap can be broken or not. As of now, latest machine learning (ML) guidance shows a 5-10% chance for strong to severe storms on Tuesday. Tough to say if trends will hold over the next few days so will keep an eye on Tuesday going forward.

Chances (20-40%) for rain persist for the rest of the week along with a continuation of above average. Highs look to remain in the mid to upper 80s Wednesday through Saturday. ML guidance shows low chances (<= 5%) for strong to severe storms. Thus, could see a continuation for strong to severe storms for the rest of the week but confidence in specific details remains low.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 635 PM CDT Sat Aug 29 2026

Largely VFR conditions expected through the period. -SHRA/-TSRA may impact areas west of the James River Valley toward the I-29 corridor late this evening and overnight (roughly 03z-08z) but confidence remains too low in coverage to include -TSRA at KHON at this time. Showers may continue east of I-29 into early Sunday morning. Heavier rain may lead to brief MVFR and lower conditions, and thunderstorms may produce gusty and/or erratic winds. Otherwise, some guidance is showing lower chances (30% or less) of MVFR visibility along the Buffalo Ridge due to fog, but confidence in development is low.

Winds through the period remain light overall with some variance in direction. Marginal speed LLWS is expected overnight at KSUX as the LLJ increases. However, stronger part of the jet will be south and east of KSUX, expanding LLWS into northwestern IA and eastern NE.

FSD WATCHES/WARNINGS/ADVISORIES

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