textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and thunderstorms continue this morning over northeastern Nebraska into northwestern Iowa. Shower/storm chances expand north today/tonight, but better chances remain across northeastern Nebraska and northwestern Iowa. The main threat is locally heavy rain.

- Patchy fog continues mainly over the higher elevations of southwest Minnesota and adjacent areas of eastern South Dakota this morning. Moderate (40-55%) chances of locally dense fog by daybreak.

- Areas of low stratus expand from south to north this morning, with low confidence on how quickly this erodes into the afternoon. This may be a recurring phenomenon through the weekend.

- Near to below normal temperatures through most of next week. Periodic showers and storms expected. Humidity lingers.

UPDATE

Issued at 343 AM CDT Fri Aug 14 2026

Patchy fog lingers through mid morning near the Buffalo Ridge. Probability of visibility below 1/4 mile has increased for this area as well, so be prepared for changing conditions.

Showers/storms continue to bloom this morning near and south of US Highway 20, where mesoanalysis indicates some WAA and increasing vorticity with an elevated boundary, somewhere between 850mb and 700mb. CAMs remain too slow with the development of this activity based on trends over the last hour. Development remains focused just south of our area, but expect this to lift north through the morning hours. Also some isolated showers north of I-90. Scattered showers and storms continue today into tonight with the mid level wave and as the surface low lifts north out of KS.

Severe weather is not expected with soundings showing a deep warm layer, relatively weak shear, and tall/skinny CAPE. Main threat remains locally heavy rain through mid to late morning; activity so far seems fairly progressive, so concern would be training storms over areas near US Hwy 20 that received heavier rainfall yesterday. Locally heavy rain remains the main threat later today as well, especially over those aforementioned areas. Severe weather remains unlikely later today into tonight with continued long/skinny CAPE profiles and a deep warm layer, precluding hail threat and limiting wind potential.

May see a break in the more widespread precipitation overnight Friday into Saturday between waves. Confidence in precip timing/coverage remains low for this time. Fog and stratus are expected to develop once again.

DISCUSSION

Issued at 118 PM CDT Thu Aug 13 2026

Upper level flow becomes a bit more southwesterly tonight into Friday, which will allow a weak wave to drift north into the area. With an elevated 1000-1500 J/kg CAPE, a freezing level around 14 kft and weak shear, locally heavy rain with slow moving storms will be the main concern. This weak mid to upper level support lingers into the afternoon and early evening, especially across parts of northwest IA, and may allow for additional showers and isolated thunderstorms. One note, the LLJ and 850 mb boundary looks to remain just south of the area so the pockets of heavier rain may stay just south as well. To the northwest of northwest IA weak capping may keep the activity more limited. For now severe weather very unlikely and flash flooding threats also look low.

Additional weak mid and upper level support moves through the area later Friday night into Saturday and may bring additional showers and isolated thunderstorms. Severe weather and flash flooding appear very unlikely.

One common theme for Friday into the weekend will be persistent and potentially difficult to dissipate stratus and patchy fog. Weak low level flow and some residual boundary layer moisture from the latest rainfall may help keep this stratus potential in place until a bit stronger push of drier air can move into the area. Sunday does look like the day with the lowest threat for any showers and storms.

Monday will see a west northwest jet max sag south into the area which should allow for heating ahead with a weak cool front trailing Monday night. This cool front could spark a few thunderstorms Monday night with isolated severe storms possible. The EC and Canadian are slower with this front than the GFS, so will need to watch trends and for now low confidence on any storms.

West northwest flow aloft remains in place Tuesday through Thursday with periodic weak waves expected to move through. This should keep shower and thunderstorm chances in place during this time with near to below normal temperatures.

AVIATION /12Z TAFS THROUGH 12Z SATURDAY/

Issued at 634 AM CDT Fri Aug 14 2026

A mixed bag of conditions through the period between showers/storms and stratus/fog. Most of the area will see MVFR and lower conditions through most of the period.

Showers/storms continue to lift north this morning, with additional showers/storms through the period. Confidence is low in the timing, so did not make significant changes from the previous forecast since trends are similar.

Fog will diminish later this morning across southwestern MN, but has been leading to visibility below 2 miles at times. Fog likely returns tonight, but too low confidence on coverage to include at any site at this time. Once ceilings drop to MVFR/IFR, they will remain there through most of the period. Some soundings indicated periods of improvement later this afternoon/evening, but too low confidence in SCT so stayed pessimistic.

FSD WATCHES/WARNINGS/ADVISORIES

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