textproduct: Sioux Falls

KEY MESSAGES

- Fog, including dense fog with visibility below half a mile, mainly across northwestern Iowa into southwestern MN. A Dense Fog Advisory is in effect for portions of the area until 9 AM CDT.

- Severe weather possible Friday afternoon and evening. Confidence remains low due to strong capping potential.

- Additional moderate to high chances (50-80 percent) for showers and thunderstorms return Saturday night into early next week. Severe risk is low.

- Cooler conditions arrive this weekend into early next week.

UPDATE

Issued at 257 AM CDT Wed Sep 9 2026

Only changes to the forecast were areal expansions of this morning's Dense Fog Advisory.

We're starting the day in the 50s and 60s with mostly clear skies. Dense fog has continued to expand early this morning, mainly across northwestern IA into adjacent areas of NE/SD/MN. Dense Fog Advisory continues until 9 AM for portions of the area, as fog is expected to lift through the morning hours.

Otherwise, a pleasant September day on tap with temperatures in the upper 70s to near 80 for most of the area. Dry with plenty of sunshine and northwesterly winds, which may gust to around 20 mph at times. Surface high pressure remains overhead tonight, with lows again the 50s. Calm to light winds and mostly clear skies may lead to some patchy fog once again tonight. More of the same, but slightly warmer Thursday as the surface high slides east and southerly flow returns.

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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 625 AM CDT Wed Sep 9 2026

Beginning to see some improvements in visibility due to fog this morning, although there remains scattered IFR to LIFR visibility across northwestern IA and adjacent areas of NE/SD/MN. Fog continues to mix out through the morning hours, and expect VFR conditions to return to the area by 14-15z.

Winds later today gust around 20 knots, generally out of the northwest. Calm to light winds return tonight into Thursday morning, which may lead to some additional patchy fog development.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until 9 AM CDT this morning for SDZ071. MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ090. IA...Dense Fog Advisory until 9 AM CDT this morning for IAZ002-003- 012>014-020>022-031-032. NE...Dense Fog Advisory until 9 AM CDT this morning for NEZ014.