textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and storms slide east into early afternoon. Severe weather risk remains low, but a stronger storm could produce small hail and 50 mph wind gusts through mid morning.

- Mostly dry this evening and tonight.

- Late Thursday afternoon and evening thunderstorms are possible along an approaching front. Best chances remain across northern and central Minnesota, with isolated risks further southwest. Storms may be capable of large hail and localized strong wind gusts.

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

UPDATE

Issued at 306 AM CDT Wed Aug 19 2026

Area of showers and storms is moving east this morning across south central SD. Severe weather risk remains low at this time, but a stronger storm in south central SD and the MO River Valley could produce 50 mph wind gusts and dime sized hail. Storms should weaken as they move away from the instability axis. This activity moves east across the area late morning/early afternoon.

No significant changes to the forecast this morning as northwesterly flow remains in place for the next couple of days. For the rest of today, think that most will stay dry later this evening into tonight with some stabilization resulting from the morning convection. Guidance does hint at some isolated activity later in the evening as the next vort lobe and WAA move into the area, although any instability tanks pretty quickly after dark. Soundings are relatively dry, so think we'll struggle with development. Severe weather risk remains low, but not zero.

Patchy fog may develop late tonight into early Thursday with lighter winds and more efficient cooling if skies remain mostly clear.

Better forcing later Thursday as the front moves through remains off to our north and east with the mid/upper level wave. That said, models still bring MUCAPE of over 1500 J/kg ahead of the front and firing off isolated storms along it. Severe risk is still low with shear around 35 knots and mid level lapse rates around 6 deg C/km, which could may be enough for isolated stronger storms with large hail and damaging wind gusts.

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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 628 AM CDT Wed Aug 19 2026

Watching a few areas of convection move east-southeast this morning, mainly across south central SD/northern NE and another near/north of US Hwy 14. Think KFSD and KSUX will miss out on TSRA, and KFSD may miss out on -SHRA all together if trends continue. Showers/storms taper down late morning/early afternoon across the area. Further east, have seen some very patchy fog leading to MVFR vis at times, which should come to an end by mid morning.

Confidence is low on any further convection this evening into tonight. Patchy fog looks to develop again by early Thursday morning, mainly in/near river valleys.

Outside of convection and fog, VFR conditions prevail.

FSD WATCHES/WARNINGS/ADVISORIES

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