textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and storms will slide across the area into the daytime hours today. Severe weather chances are low, but the strongest storms will be capable of wind gusts to 50 mph and small hail mainly in south-central South Dakota and along the Missouri River Valley.

- Late Thursday afternoon and evening thunderstorms possible along an approaching front. Best chances in Northern and Central MN, but isolated risks also further southwest. Large hail and localized strong winds main risks.

- Mostly dry conditions heading into the weekend with highs either side of 80 degrees. Morning rain on Sunday is possible.

UPDATE

Issued at 938 PM CDT Tue Aug 18 2026

Storms over southwest Minnesota and northwest Iowa earlier this evening have diminished and pushed east of the area. The weak surface frontal boundary responsible for those earlier storms continues to drift southeastward, with further development unlikely as inhibition builds. So next we'll keep our eyes out to ongoing storms in western South Dakota and eastern Wyoming that will drift eastward through the overnight hours, driven by a continued active northwest flow pattern. So like the past couple of nights, will have to see if this activity could maintain any severity as it moves into our area.

MUCAPE values will linger in the 1000-1500+ J/kg range mainly in south-central South Dakota, with instability decreasing with northward extent across the central part of the state. Effective shear values will be sufficient to sustain convection as well, so thunderstorms do at least appear likely west of the James River by 3-4 am. Chances for severe weather with this look very low given weak mid level and low level lapse rates and weak mid level flow. However, a stronger wind gust up to 50 mph and small hail can't be ruled out mainly in south-central South Dakota through daybreak. Storms should weaken quickly as they move east as they encounter more stable air; however, some rain and general thunderstorms will continue to be possible through the early afternoon hours as the activity gradually pushes east.

DISCUSSION

Issued at 106 PM CDT Tue Aug 18 2026

THIS AFTERNOON: A weak frontal boundary continues to sink southward early this afternoon, with noticeable strato-cu field developing along the Highway 20 corridor. The remainder of the afternoon is likely to remain dry in most locations, outside of very isolated development along this aforementioned boundary.

THIS EVENING/TONIGHT: Some guidance shows isolated development this evening along a weak convergence zone in SW Minnesota and northern Iowa. This convection may also be sparked by a weak area of vorticity dropping through the Dakotas from the northwest. Any storm that develops will be in an area of MLCAPE AOA 1000-1500 J/KG, with sufficient shear to promote perhaps a rotating storm. Anticipating the severe weather risks to remain low.

Further west, additional convection is expected to form over the Black Hill region this evening as a stronger wave enters the area. The track of this wave, along with how the LLJ propagates overnight, should push some of this activity into south central SD after 1am. MUCAPE remains quite low, with marginal mid-lvl lapse rates, so widespread severe weather is not anticipated. Though, a few gusty wind gusts could remain possible through 3am. There remains reasonable agreement that this convection could track along the MO river valley into eastern Nebraska by daybreak. This is an area where higher PoPs will be focused.

WEDNESDAY: The departure of this shortwave should lead to a period of subsidence and quiet weather well into Wednesday. Cloud cover may be more substancial over the southern half of the CWA thanks to mid- upr clouds from convection. By the afternoon southwesterly surface winds will return, allowing high temperatures to rise into the upper 70s to lower 80s. Convection risks in the afternoon and evening may be quite narrowed to a zone ahead of an approaching surface front in north central SD. Further southeast, there doesn't seem to be any strong focusing mechanism, with weak convective inhibition likely keeping the area free of any isolated larger storm growth. While surface and low-lvl focus remains absent, we'll need to watch the presence of any weak vorticity in the NW flow. Further northwest, any convection that develops along the frontal boundary may try to track southeast, though lessening instability should limit the overall severe risks.

THURSDAY: Any precipitation risk continues to look minimal heading into Thursday morning as a stronger EML begins to build into the region. Southwesterly surface winds overnight may keep overnight low temperatures from falling significantly. The aforementioned surface boundary from Wednesday will sink southeast through the day on Thursday providing a focus mechanism for storms by late afternoon and evening. MLCAPE approaching 2000-3000 J/KG may develop along this boundary as dew points try to quickly surge northward. The lingering questions for convective development are focused on the track of mid-lvl vorticity in the late afternoon, along with convective inhibition ahead of the boundary. The track of shortwave energy could favor more development in central and northern Minnesota, with only isolated storms further southwest along the boundary. While instability is greater, shear is a bit more marginal suggesting less organization to anything that develops.

FRIDAY-MONDAY: Mid-lvl heights begin to rise over the Rockies as the ridge amplifies. The lingering, but sharper, NW flow pattern over the Dakotas may bring one more wave into the region Friday. However the southward passage of Thursdays front should push the best boundary layer moisture south of the area. The ridge axis begins to push eastward as we move into the upcoming weekend. A pleasant Saturday is likely in the region with highs either side of 80. Increasing low-lvl warm advection into Sunday could bring elevated showers and thunderstorms eastward into Sunday morning, along with more clouds and slightly warmer highs into the lower to middle 80s. At this time, rain coverage may be limited with only a 20-30% PoP.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1237 AM CDT Wed Aug 19 2026

Scattered showers and thunderstorms will move across the area from generally west to east through the morning hours and into the early afternoon. The strongest activity with this will mostly be contained along and south of the Missouri River Valley, though weaker thunderstorms will be possible farther north as well. Outside of the thunderstorms and some of the heavier showers, VFR conditions are expected.

Winds will be mostly light and variable through the period, only picking up slightly Wednesday afternoon out of the south- southwest around 5-9 kts. Winds will turn light and variable once again Wednesday night, except near and west of the James River where winds will stay in that 5-9 kt range even after sunset.

FSD WATCHES/WARNINGS/ADVISORIES

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