textproduct: Sioux Falls

KEY MESSAGES

- Considerable cloud cover, drizzle, and fog will continue to move southeast this afternoon, but will diminish by mid-late afternoon.

- A somewhat unsettled weather pattern with low predictability will begin to bring daily risks for thunderstorms into next week. A few of these may be strong to severe.

UPDATE

Issued at 358 AM CDT Fri Aug 7 2026

Taking a look across the area, the forecast remains on track with the main focus being on the developing fog and showers. Starting with fog, elevated dew points and a slightly warmer air mass aloft have led to some advection fog developing this morning. While coverage is mostly patchy, there could be a few locally dense areas mainly along our waterways and low-lying areas where visibilities as low as 1 mile will be possible. With this mind, make sure to drive with caution when making those morning commutes. Shifting to our precipitation chances, we continue to see scattered showers with isolated thunderstorms developing this morning mainly in response to a nocturnal LLJ and bits of isentropic lift ahead of a cold front.

While we could see this activity fester across parts of the area over the next several hours, most guidance continue to highlight portions of southwestern MN as the main area of concern for anything stronger as the cold front approaches. IF a stronger storm or two can get going, the main concerns would be large hail up to golf ball size and damaging winds up to 60 mph. Nonetheless, with the fairly progressive nature of the front; the window for any stronger activity would be narrow maybe 2-4 hours at most with the focus being between 6am-10am. Lastly, should see quieter conditions return into the early afternoon with highs mainly in the low to upper 80s expected.

DISCUSSION

Issued at 202 PM CDT Thu Aug 6 2026

THIS AFTERNOON: Weak troughing sliding through the region this afternoon has kept a narrow corridor of mid-lvl moisture stretching from northern Nebraska into western Minnesota. This moisture, confined within an area where H850 mb flow 30-40 knots, may eventually lead to isolated high based showers or thunderstorms later this afternoon. Confidence on development remains low, and will keep PoPs below 20% ATTM. Elsewhere, southerly winds are increasing, finally mixing out low-stratus and fog. High temperatures climb into the upper 80s west of the James River to the lower 80s further east.

TONIGHT: Two concerns in the overnight period. First of all, southerly winds should continue to transport low-lvl moisture northward, pushing dew points into the mid-60s. Should winds weaken sufficiently and temperatures drops not be overly impacted by widespread wildfire smoke aloft, then areas of fog may once again develop along and south of I-90. HREF probabilities focus a 70% probability of <1 mile visibility along and southeast of a line from Yankton to Windom. However, if the second concern we'll discuss next takes place, then those fog probability may drop significantly.

That second concern is a risk for elevated convection by daybreak. The pesky quasi-northwest flow has the potential to bring subtle mid- lvl vorticity into the area by daybreak. Guidance is all over the place, which is typical in this setup, suggesting either minimal to no convection, or fairly widespread storm development. From a parameter perspective incoming CAA AOA 850:700 mb will create a steepened mid-lvl lapse rate, but also push MUCAPE over 2000 J/KG. Shear remains a bit marginal AOA 20 knots, suggesting convection may stay a bit less organized. However analog soundings indicate potential for golf ball hail with freezing levels near 11K ft AGL, with some modest mid-lvl dry air also suggesting a few stronger wind gusts that may make it through the stable boundary layer. If this threat develops storms would push southeast with the mean flow and exit late morning.

FRIDAY: The initial morning convection will precede a cold front that will push southeast during the day. Temperatures behind this front will not be all that cool, with highs again climbing into the lower to middle 80s. The rest of the day and evening will be quiet. After midnight however, some guidance is showing another wave moving through central SD and into NE. Should this wave develop, there may be sufficient convergence on the LLJ to induce scattered convection in central and south central South Dakota after 3am. Isolated hail will be the most likely risk with these storms.

SATURDAY/SUNDAY: There remains quite a bit of uncertainty heading into the upcoming weekend given the synoptic flow pattern. Saturday morning convection should continue to push away from the CWA in the morning hours, which would suggest stabilization in the Tri-State area for the rest of the day. However the nocturnal ignition of the LLJ would pose some risk for renewed elevated storms into Sunday morning south of I-90. There seems to be a bit more agreement by late Sunday into Monday as a stronger wave moves through the Dakotas late in the evening. Depending on the degree of instability in the region, this could serve as a reasonable setup for a nocturnal MCS given the intensifying 850mb southerly flow and increased mid-lvl westerlies. Continue to monitor severe weather outlook risks into Monday morning.

MONDAY-WEDNESDAY: There will really be no change in the forecast into the middle of the week as the region remains under slight northwesterly flow aloft. This flow will keep a persistent risk for daily convection, though with extremely low confidence and predictability until a day or so before. Temperatures may fall back slightly into the lower to middle 80s near the seasonal normals.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1150 AM CDT Fri Aug 7 2026

Frontal boundary continues to slide southeast early this afternoon. Immediately preceding the passage of the front we continue to see IFR ceilings and even drizzle move southeast. Continued mixing behind the boundary will erode this stratus fairly quickly, but cloud cover will spread southeast into NW Iowa this afternoon. Northwest winds may gust to 20-25 mph at times into early evening.

Clear skies are expected overnight, with lingering wildfire smoke aloft. Mid-lvl clouds form over south central SD after midnight, with this area of clouds and potential sprinkles/showers moving northeast towards I-29 by mid-late morning. VFR conditions are likely.

FSD WATCHES/WARNINGS/ADVISORIES

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