textproduct: Sioux Falls

KEY MESSAGES

- Showers and thunderstorms are likely again tonight into Thursday morning. The main threats will be locally heavy rain (better chances south of I-90) and strong winds up to 70 mph (better chances near the Missouri River into parts of northwest IA).

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

- Cloud cover and cooler temperatures move in for Thursday into the weekend. Periodic showers and storms expected. Humidity lingers.

DISCUSSION

Issued at 121 PM CDT Wed Aug 12 2026

A pair of waves move onto the Plains tonight. The first will be associated with the right entrance region of the upper jet to the northwest. This may bring some some stronger storms to central SD later this evening. An isolated severe storm will be possible. Later tonight a more subtropical wave moves from CO into northern NE and may interact with a much more unstable environment. If this develops it will likely become linear with heavy rain and wind gusts to around 70 mph likely. The better chances for this coming together will be near the Missouri River into northwest IA, likely from about 2 am to 7 am. CAPE values likely running about 20000-4000 J/kg with moderate deep layer shear.

Once this activity exits the area, fairly stable air settles in for much of Thursday into Thursday evening. Thursday morning may see some low stratus and patchy fog, with these clouds lifting a bit but likely lingering through the day. This should limit warming a bit with highs likely remaining in the 70s. However with these cooler temperatures will not come a drop in humidity with dew points still likely in the mid 60s to lower 70s.

Later Thursday night into Friday morning a weak wave will lift north into the area and should bring weak to moderate warm air advection in the low to mid levels. With the potential for maybe 1000 J/kg CAPE a few thunderstorms will be possible, with the better chances in northeast NE and northwest IA. Severe weather is unlikely but local heavy downpours are possible.

Friday afternoon and Friday night weak upper level ridging will build and likely suppress any convective activity. However Saturday into Saturday evening showers and thunderstorms will likely redevelop with very isolated severe storms and locally heavy rain possible.

Faster northwest flow aloft will be north of the area Monday through Wednesday next week. This will keep a slightly cool air mass in place during this time with highs generally from 75 to 85 each day. Periodic weak waves will move through and bring chances for showers and thunderstorms with low confidence on strength and timing right now.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1221 PM CDT Wed Aug 12 2026

The biggest concern for this time frame will be the threat for showers and thunderstorms, with the most likely time later tonight into early Thursday morning. Areas near and north of the Missouri River into parts of northwest IA will see the bigger threat for locally heavy rain and wind gusts of 50 to 70 mph with the strongest thunderstorms.

Otherwise some patchy MVFR conditions are possible in northwest IA through mid afternoon. IFR to MVFR ceilings and possibly some patchy fog are possible later tonight and Thursday morning as well.

FSD WATCHES/WARNINGS/ADVISORIES

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