textproduct: Sioux Falls

KEY MESSAGES

- Cluster of severe storms with damaging winds up to or locally exceeding 75 mph will move through portions of the Missouri River Valley early this morning.

- Areas of dense fog and low stratus may form again late tonight into Wednesday morning, though confidence in coverage is low.

- Following a warm and dry Wednesday, an influx of moisture will bring a chance of thunderstorms into Thursday. Very uncertain, but a highly localized heavy rain risk could develop.

- Cloud cover and cooler temperatures move in for Thursday and Friday, along with another risk of rain Thursday night.

UPDATE

Issued at 245 AM CDT Wed Aug 12 2026

With ongoing severe weather across northern Nebraska, this update will be short and sweet. An ongoing MCS continues to propogate to the southeast this morning just south of the SD/NE state stateline. While gradual weakening has occurred, this system is starting to take an eastward turn towards the U.S. Highway 20 corridor as of 3 am. As a result, a downstream severe thunderstorm watch has been issued for portions of eastwestern NE and western IA through 10 am with Dakota and Dixon Counties being the main focus for our area. The main hazard would be wind gusts between 60-70 mph with a secondary threat being margially large hail up to quarter size.

DISCUSSION

Issued at 115 PM CDT Tue Aug 11 2026

THIS AFTERNOON: VERY humid conditions continue early this afternoon, but a wide array of temperatures in the region. Early morning stratus and fog has kept a lid on temperatures north of I-90, but south of the Interstate we've seen highs climb towards the 90s. Heat index in a few areas may reach the 100 degree mark. A couple patches of ACCAS based AOA 600 mb continue to move along I-90 this afternoon, but development potential remains low as this moves into NW Iowa. Will continue to monitor.

THIS EVENING/TONIGHT: CAMS continue to struggle resolving the myriad of weak forcing waves moving through the Plains, and these trends continue today. The result is sporadic convection developing over the western High Plains in the late afternoon and evening and then gradual tracks southeast overnight. Despite the high level of instability across the Dakotas, very few strong focusing mechanisms for convection remain apparent this afternoon. What may happen is gradual upslope flow over the western Dakotas combined with increasing SE 850mb flow could induce a cluster or two of storms. This activity will tend to follow the mean flow and push east southeast into the overnight hours. However, a closer look at soundings continues to show fairly strong inhibition both to surface based parcels but also to elevated parcels. So with that in mind, planning on keeping PoPs low, with some focus along I-90 and areas moreso over the Missouri River valley. Continue to monitor trends this evening, as strong storms could bring some higher wind gusts if they survive.

Higher confidence again in the development of stratus and fog given the continued light northeast wind and trapped boundary layer moisture. Much like this morning, areas of locally dense fog may form with widespread stratus potential possible.

WEDNESDAY-WENDESDAY NIGHT: Assuming stratus/fog does not hinder the warmup tomorrow significantly, we'll continue to see another warm afternoon on Wednesday with dry conditions. Dew points will remain in the 70s, which should cap high temperatures in to the middle 80s. A slight shift in the mid-lvl flow begins Wednesday, with persistent ridging over the Four Corners translating eastward into the Southern Plains through the day. This will result in pulling a sub-tropical moisture plume with embedded vorticity northward through the Rockies and into the Plains late in the day and overnight. Slightly better signals for convection tied to this wave will begin to focus over western SD/NE late in the afternoon, with rain gradually shifting eastward into Thursday morning. The severe weather risks remain on the lower side but not non-zero as some lingering wind threat could present itself along the MO river valley. Mid-lvl lapse rates quickly worsen as you move into the overnight hours however. One noticeable thing to watch is the increasing PWAT values which approach 1.75" by Thursday morning. This could signal at least the potential for highly localized heavier rain amounts, which the HREF PMM signals in the 2-4" range. The key to watch will be where the residual surface boundary falls by late Wednesday, as this could pull better convection risks south of the CWA.

THURSDAY-FRIDAY: Quite a bit of cloud cover may be in the area for Thursday as cooler northeasterly flow returns and we'll be on the edge of the baroclinic zone to our south. At this point, highs in the 70s are likely, with a gradually increasing rain chance into Friday as mid-lvl flow shifts back to the southwest, mid-lvl vorticity slides through the Central Plains, and the baroclinic zone lifts northward. The highest PoPs will be focused Thursday night into Friday.

SATURDAY-MONDAY: A flattened mid-lvl ridge remains over the central CONUS into the upcoming weekend, bringing another risk for rain by Saturday as energy tracks back northward into the Upper Midwest. Confidence is rising that we'll see a dry Sunday and Monday as high pressure arrives, mid-lvl ridging shifts back westward, and quasi- northwest flow moves back in. Temperatures may begin to rise back into the 80s by Sunday and Monday.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1255 AM CDT Wed Aug 12 2026

Monitoring a severe wind-producing cluster of storms in south central SD at the start of this period. Trajectory most likely takes the greater risk of severe winds just south of KSUX, but will closely monitor for a northward shift in the trajectory as it moves east near the Missouri River Valley. Projected timing would bring a potential for storms near KSUX by 09Z-10Z if storms track that far north.

Otherwise areas of MVFR to locally IFR visibility in fog is the greatest concern into mid-morning Wednesday, though probability of sub-VFR conditions at KHON/KFSD is too low to include in the TAF at this time.

Chances for additional showers/storms increase late in this period, but confidence is too low to include in the TAFs at this time.

FSD WATCHES/WARNINGS/ADVISORIES

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