textproduct: Sioux Falls

KEY MESSAGES

- Scatttered showers and storms continue this morning as an MCS passes through the U.S. Highway-20 corridor. Strong wind gusts up to 75 mph and small hail are the main harzards.

- Isolated flash flooding will be possible this morning mainly across the Highway-20 corridor as multiple rounds of showers and storms progress through the area.

- 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.

UPDATE

Issued at 246 AM CDT Thu Aug 13 2026

Taking a look across the area, the focus continues to be on the strengthening MCS across northcentral and northeastern Nebraska as it progresses east-northeastwards this morning. The latest observations out of Loup City, Nebraska recorded gusts between 60-80 mph within the main bowing segment. With its current trajectory, this system would make its way into areas along and south of the Highway-20 corridor between 3am to 4am with the main hazards being wind gusts up to 75 mph and small hail. With this in mind, a Severe Thunderstorm Watch is now in effect for portions of the Highway-20 corridor through 8am. Given the moisture rich and decently unstable environment ahead of the system, current thinking is it should maintain its current intensity heading into the lower Missouri River Valley and portions of northwestern IA. Otherwise, we'll also have to monitor rainfall accumulations as moderate to heavy rainfall could lead to isolated flash flooding in our urban areas and lower spots. Lastly, should see most of this activity exit our area closer to 8am to 10am. Dreary conditions will persist for the day with highs peaking in the low to upper 70s for the day.

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 /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1237 AM CDT Thu Aug 13 2026

Areas of rain along with some embedded thunderstorms will continue to push through the area through the early morning hours. Storms could be on the stronger side near and south of Highway 20 where gusty winds to around 50 kts will be a possibility in the strongest activity. Rain will gradually taper off through the daytime hours, though a lingering showers will be possible through the afternoon and evening. Showers and storms may increase in coverage towards the Highway 20 corridor by the very end of the period, but confidence is low on this potential.

After the early morning rain ends, lingering low stratus will be possible through at least the early afternoon, though there's moderate confidence in timing of when this stratus lifts and so changes may be needed in future forecasts. Winds will be mainly out of the east-northeast through the period, occasionally gusting to around 20 kts during the daytime hours today.

FSD WATCHES/WARNINGS/ADVISORIES

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