textproduct: Sioux Falls

KEY MESSAGES

- Patchy fog is possible tonight across mainly northwest Iowa. Any fog that develops will dissipate during the morning hours.

- Severe weather possible on Friday afternoon and evening. Confidence is low due to the potential for a stronger cap.

- Additional very good chances (50-80 percent) for showers and thunderstorms return on Sunday.

- Cooler conditions arrive this weekend into early next week.

UPDATE

Issued at 831 PM CDT Tue Sep 8 2026

The last of the rain showers have finally pushed southeast of the forecast area this evening. Dry conditions are expected for the rest of the night. Weak surface ridging will slide into the area tonight, allowing for winds to go light and variable. Some residual moisture looks to remain across mainly northwest Iowa. This looks to lead to some patchy fog development during the overnight hours tonight. Any fog that develops will mix out during the morning hours tomorrow.

Wednesday will be a beautiful day with highs warming to the 70s and low 80s along with marginally breezy northwest winds. With dew points falling to the 50s to low 60s, humidity will be much lower than what we have experienced the past few days. High pressure slides through the area Wednesday night, resulting in southerly return flow for Thursday. Highs will warm a little bit more, with all locations pushing into the 80s. The southerly winds will be more on the breezy side with gusts up to 20-30 mph through the afternoon hours. Dry conditions are expected for the day as well.

DISCUSSION

Issued at 111 PM CDT Tue Sep 8 2026

The right entrance region of the upper level jet will move across the area this evening, helping increase convergence along the low to mid level boundary. Much drier air was filtering in behind the surface front, with 30 and 40 degree dew points in central SD. With 1500-2000 J/kg CAPE ahead of this front and about 40 knots of deeper layer shear, a few stronger updrafts will be possible later this afternoon. For now the better chances appear to be from northeast NE towards Storm Lake and points south. The main severe threat should exit the area by early evening as cooler and drier air settles in behind the exiting right entrance region.

Wednesday should prove to be a pleasant day with decreased humidity and seasonally warm temperatures in the upper 70s to lower 80s. Northwest winds may gust as high as 25 mph, with lighter winds across northwest IA. High pressure at the surface will drift across the area tonight and allow for some cool morning lows, mainly low to mid 50s but a few lower spots could see lows as cool as the upper 40s.

Upper level troughing digs across the Northern Rockies Thursday which will swing lower level winds around to the south, allowing for slightly warmer temperatures, generally lower to mid 80s.

As this upper level trough spreads onto the Plains Friday, an environment that potentially supports severe weather will set up. The challenge that day will be breaking the cap. If the cap can be broken, 2000-3000 J/kg CAPE along with about 30-40 knots of deep layer shear would support a few severe updrafts.

Once this front moves through Friday night, much cooler air will settle into the region. Highs Saturday through Monday will likely be in the 70s, with some 60s possible on Sunday. Lows each morning should be roughly 45 to 55.

Sunday into Sunday night will see another fairly strong trough move through which increases warm air advection and should bring fairly widespread showers and thunderstorms. For now any sever weather looks to remain very isolated.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1231 AM CDT Wed Sep 9 2026

Fog has begun earlier than previously anticipated. Some locations are already showing ceilings and visibilities down to LIFR levels. A weak boundary is currently draped from approximately KMWM down to KVMR and will not move much through the night. This will keep the better moisture pooled ahead of it and allow fog to not only persist but likely spread across most of northwest Iowa, parts of Jackson county in southwest Minnesota, and possibly into far northeast Nebraska, bringing LIFR conditions with it. The fog will begin to lift tomorrow morning as the boundary begins to pick up speed. This will leave VFR conditions for the rest of the TAF period with marginally breezy northwest winds for the afternoon hours.

A few hi-res models show the potential for sprinkles/light showers to develop across parts of southeast South Dakota and southwest Minnesota, early tomorrow morning. Have left out of TAFs for now but trends will be monitored through the night.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ012-013- 020-021. NE...None.