textproduct: Sioux Falls

KEY MESSAGES

- Patchy areas of fog will continue through mid-morning mainly across our waterways and low lying areas.

- Scattered showers and thunderstorms will return this evening. A few storms may become severe with 2 inch hail and 65 mph winds being the primary threats. Overnight storm chances will continue through at least Wednesday with the potential for stronger storms.

- Morning clouds and wildfire smoke aloft will continue to affect daytime heating leading to highs mainly in the 80s to low 90s through Wednesday. Cooler conditions will return by late week with highs in the 70s.

UPDATE

Issued at 425 AM CDT Mon Aug 10 2026

Taking a look across the area, we're continuing to see developing showers weaken across central SD mostly due to the increasing inhibition further eastwards. While this activity should continue to feaster mainly north of I-90, any accumulations will be limited (If any). From here, should see any lingering precipitation and stratus gradually dissipate by mid-morning as diurnal resumes. Highs will max out in the low to upper 80s with light southeasterly winds. Otherwise, the forecast remains on track for additional showers and thunderstorms this evening and overnight. Still looking like clusters of showers and storms will likely develop across western/central SD then follow the mean west-northwestly flow into our area.

CAMs are still a bit split on if things can congeal into an organized line or not. Based the orientation of the northern stream jet, there could be either a broken line or multiple cluster segments with this developing activity. With this in mind, large hail up to 2-inches will be the main hazard with initial clusters. When things grow upscale and become outflow dominant, damaging wind gusts up to 65 mph will become the main concern. Lastly, timing is still a bit uncertain due to differences in the progression and evolution of this activity. As a result, a rough estimate of 9pm-6am is about as close as we can get right now. As newer runs of guidance come in, further refinement to the timing are this activity are expected.

DISCUSSION

Issued at 122 PM CDT Sun Aug 9 2026

THIS AFTERNOON: Cool northeasterly surface and low level flow has brought widespread stratus into the region this afternoon. We're gradually seeing this cloud layer mix-out, which should still result in a brief window of highs in the lower 80s. Further west, lots of mid-high level AC moving eastward towards the central Dakotas. These clouds, tied to weak dPVA at the 600:500 mb layer, will continue to push eastward this evening. Below this cloud layer, soundings indicate a very stout and deep dry layer which should prevent anything more than a few sprinkles reaching the ground later this afternoon/evening.

TONIGHT: A very tricky and uncertain forecast continues into Monday, as no clear forcing mechanisms to develop convection are present at this point. Despite the pesky northwest flow pattern, most CAMs and global models have backed off on surface based convection over the western Dakotas this afternoon and evening. The thick layer of smoke aloft could potentially cause some limitation on convective development, but also the lack of any clear defined shortwave in the flow. Now with that said, there are a few hints at some weak 700 mb warm advection trying to develop after midnight (perhaps closer to 3-4am) into central South Dakota. A parcel lifted off the 700 mb layer should have upwards of 2000 J/KG MUCAPE with upwards of 25 knots of shear. Thus if a storm develops, it could briefly produce golf ball size hail and some modest wind gusts. The eastward movement of this activity beyond the James River should be limited by lingering low-lvl dry air. Elsewhere, given low-lvl subsidence continuing into the overnight hours, along with boundary layer dew points in the 70s, there will also be concern for fog/stratus development.

MONDAY: Any morning convection should again weaken by mid-morning, leaving potential stratus and fog in place through the morning in a light east southeast wind. Eventually temperatures do rise into the low to middle 80s, but smoke aloft could again limit the rise of temperatures. There still appears to be a better signal for a passing shortwave Monday night into Tuesday capable of producing evening convection over the western Dakotas/Nebraska. The residual moderate elevated instability, and steepening mid-lvl lapse rates, combining with an increasing nocturnal LLJ should be able to produce one or more clusters of stronger storms moving eastward towards central SD into the overnight hours. However soundings present more and more inhibition as storms move into the CWA.

TUESDAY: A bit of a rinse and repeat forecast for Tuesday as we may again start the day with stratus and some fog and even a few lingering elevated thunderstorms. Gradual upslope flow on the Plains Tuesday afternoon/evening may again develop one or more clusters of convection that may move towards the CWA into Wednesday morning.

WEDNESDAY: Wednesday continues to look like a quiet day in the region with more influence from minor ridging in the Plains. Temperatures with a light wind will rise towards the lower to middle 80s. By the overnight hours, some potential for MCS activity in KS/NE will attempt to move eastward and could bring some thunderstorm risks to the MO river valley.

THURSDAY-SATURDAY: Confidence remains rather low in the extended as the mid-lvl pattern shifts from a quasi-northwest flow to zonal by the end of the week. Several waves are likely to traverse these westerlies in the weekend, but a wide array of solutions continues to keep lower PoPs (20-30%) for multiple days. In reality, chances are likely going to be more limited than the NBM would suggest, however model spread will need to tighten before a better timing could be had. Confidence is a bit higher on the slight cooldown of temperatures into the 70s into next week.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 632 AM CDT Mon Aug 10 2026

Mainly VFR conditions with occasional MVFR to IFR cigs are expected this TAF period. Taking a look at satellite imagery, low hanging stratus along the Missouri River Valley has promoted MVFR to at times IFR cigs this morning along with patchy fog. Current thinking is these lower bases should gradually erode with diurnal heating closer to mid-morning giving way to more VFR conditions. From here, the focus turns to this evening as scattered showers and thunderstorms make their return. Added TEMPO groups to both KFSD & KHON to time in the developing activity. Decided to also add a PROB30 group to KSUX just in case some showers develop just south of the main activity. Otherwise, light southeasterly are expected through Tuesday morning.

FSD WATCHES/WARNINGS/ADVISORIES

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