textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and storms move east overnight. Discrete cells are capable of producing 1-2" hail and wind gusts to 60 mph. Linear segments will be capable of wind gusts to 70 mph and marginally severe hail.

- Lingering rain/storms this morning push the greatest risk of severe storms Tuesday afternoon and evening further south. If clouds clear and a storm can develop, it could be severe with wind and hail the main threats.

- Rain chances persist Wednesday and Thursday, though storm track leads to lower confidence in where rain may fall. Below to near seasonal temperatures prevail.

UPDATE

Issued at 148 AM CDT Tue Aug 18 2026

Storms along the MO River which were severe have weakened below severe limits. Attention turns to the two complexes of storms moving southeast out of central SD which are tied to the next wave and LLJ. Still some questions in the severity of these as they move east and the potential for them to grow upscale.

The first of these segments is our western fringes as of our forecast area as of 1 AM CDT. Have seen a few strong to severe wind gusts, and these storms are initially on a gradient of higher DCAPE (but higher values further to the south) and the edge of 850 mb WAA. Mid level lapse rates remain around 6 deg C/km through the morning hours with elevated instability, although soundings show this quickly weakening through 3-4 AM CDT. Will also keep an eye on the second cluster, which the HRRR and RAP showing to be the one to maintain strength longer after the first cluster dies. Not sure how much stock to put in this solution as the second cluster seems to be following exactly behind the first, which should work over the environment. That said, will likely still see sporadic strong to severe storms through 4 AM. Main threat will be wind gusts to 65 mph, although quarter sized hail with more isolated updrafts.

For the rest of today, we'll see chances for isolated to scattered showers and storms return to the area, especially if we can clear out. CAMs remain all over the place with the timing and coverage. IF we clear out and a storm can develop, can't entirely rule out a stronger storm with shear around 40 knots over the area, but confidence is low with the better forcing to our south.

DISCUSSION

Issued at 132 PM CDT Mon Aug 17 2026

THIS AFTERNOON: Convection risks remain the primary focus in the upcoming 24 hour period, as there continues to be uncertainty on if we can advect sufficient moisture northward, and provide enough focus of lift. Visible satellite this afternoon shows two areas of interest, one area of ACCAS across northeastern South Dakota and west central Minnesota, driven by 700 mb winds over the crest of the Ridge. A second area of ACCAS drifting eastward out of the Badlands area. At the surface, one concern has been a slower arrival of boundary layer moisture as surface dewpoints continue to linger in the upper 50s to lower 60s. Further south, models continue to overestimate dew points in NE/KS, providing some doubt on if the lower 70 dewpoints advertised by "high instability" models can be realized.

The projections into the evening remain slightly uncertain with several focusing mechanisms available. A surface trough extending from NW Minnesota into NE South Dakota and central South Dakota will provide some minor convergence (focused greater over NW Minnesota and eastern North Dakota). A weaker pre-frontal trough in the NE Panhandle into the Sandhills could also serve as a focal point. Finally, a few storms may also develop over the Minnesota River valley downstream of the Buffalo Ridge. Any storm that develops off of these features will likely produced an increased risk for 1-2" hail, but also 60-70 mph winds as MLCAPE pushes 2000+ J/KG and effective shear climbs towards 40 knots. Gradual east southeast storm tracks within the mean flow are likely which could put portions of SW Minnesota and the MO River valley into a higher early evening risk. However the likely overestimation of surface dew points, poor focus of convergence, and weak inhibition, may also work to prohibit convection over a large part of the Tri- State area into the evening.

Further west, additional isolated to scattered convection may form over the western High Plains late this afternoon and evening slightly stronger synoptic lift enters the area. One or more clusters of storms could reach the western CWA by mid-late evening, bringing risks lower risk for hail, but higher risks for a few stronger wind gusts. There continues to be some agreement in mesoscale and lower resolution guidance that a subtle wave crossing the Dakotas could keep scattered convection risks moving through the CWA until at least 4am. Weakening instability, and worsening lapse rates should result in fewer strong to severe storms by daybreak Tuesday. All this to say, coverage of this activity remains highly in doubt, which will keep areal PoPs lower in general.

TUESDAY: Latest guidance continues to trend the greatest risks for severe convection southward on Tuesday. Overnight convection, along with the passing shortwave should stabilize the area considerably by daybreak, with a lingering marginal risks for some crossover hail risks near 12Z. We may however see quite a bit of stratus behind this wave, suggesting cooler than normal temperatures into the afternoon.

WEDNESDAY-THURDAY: Upper troughing moving into Hudson Bay will sharpen the NW flow over the Plains slightly by mid-week. EC/GFS indicates vorticity crossing from the Pacific Northwest through the Northern Rockies early on Wednesday pushing mid-lvl lift towards the region early Wednesday. Differences on the track of this wave keep PoPs lower, with GEFS/GFS further northeast, and the EC leading to more impact through central Nebraska instead. Another wave, along with a weak frontal boundary approach Thursday afternoon. Depending on the amount of inhibition nearby, a few thunderstorms could form along this boundary late in the day.

FRIDAY-SUNDAY: Mid-lvl heights rise and the ridge sharpens over the Rockies as we move into next weekend. This transition of mid-lvl flow could bring one final risk for elevated showers/TSRA early Friday, but generally quiet and dry conditions then develop into the weekend. Temperatures however will fall more under the influence of Canadian high pressure in the Dakotas, suggesting highs may stay in the upper 70s to lower 80s.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1259 AM CDT Tue Aug 18 2026

VFR to MVFR conditions expected for this period. Two areas of showers and thunderstorms are ongoing at issuance. One area along the southern Missouri River is moving southeast into northwest Iowa. Short term guidance is in low agreement on thunderstorm evolution and uncertainty is high. Current mesoanalysis indicates the southerly storms are becoming elevated, which will reduce the overall severe threat. Still, wind gusts up to 60 mph and marginally severe hail remain possible through the next couple hours.

The second is just reaching the western border of the CWA between Huron and Chamberlain. These storms are showing signs of upscale growth into broken lines. These will continue to progress southeast through the overnight hours. Currently these storms are producing gusts of 45-50 mph. As the LLJ begins to increase these storms have the potential of increasing in severity. Should a more organized line with bowing segments form, severe winds to 70 mph are possible.

All storms should be clear of the region by late morning Tuesday. The remainder of the period should be dry with light winds. Clouds will slowly break up through the afternoon.

FSD WATCHES/WARNINGS/ADVISORIES

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