textproduct: Sioux Falls

KEY MESSAGES

- Isolated to scattered storms remain possible late afternoon and evening, through development remains very uncertain. Risks of 1-2" hail and 60-70 mph will be possible.

- Greater storm potential arrives very late this evening and more likely overnight, with potential for a few bowing clusters of storms with gusty winds and marginal hail.

- Lingering rain early Tuesday will push the greatest risk of severe storms Tuesday further south. However cooler temperatures and clouds may linger deeper into the day.

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

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 /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1212 PM CDT Mon Aug 17 2026

VFR conditions continue at mid-day, as a scattered mid-lvl cloud field continues to drift east of I-29. We'll continue to see a slow influx of moisture northward this afternoon, and combined with diurnal heating should result in scattered CU.

Convection chances really remain uncertain this afternoon and evening. We are watching a subtle wave crossing the Black Hills region which may reach the MO river valley by mid-afternoon. This high based ACCAS could spark a few showers or even develop further.

Any convection risks later this evening continue to appear isolated in nature, with better focus into the overnight hours as a wave approaches from the west. Given the uncertainty in this wave/convection along with time in the TAF, will continue to opt for Prob30 groups to show low probabilities.

FSD WATCHES/WARNINGS/ADVISORIES

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