textproduct: Sioux Falls

KEY MESSAGES

- Very light rain, sprinkles, or drizzle will be possible Wednesday afternoon into the evening.

- Rain, potentially heavy, will be possible late Thursday night into Friday. While uncertainty remains on the axis of heavy rain placement, some minor impacts to rivers and streams could be possible.

- Near normal temperatures persist this weekend and into next week. Any precipitation chances are likely to remain light and non-severe through the weekend.

DISCUSSION

Issued at 1232 PM CDT Tue Sep 15 2026

THIS AFTERNOON: Sunny skies continue Tuesday afternoon as dry air filters into the region. Temperatures will continue to rise into the upper 60s to lower 70s.

TONIGHT: Most notable change tonight was to continually lower dew points from the NBM guidance. Short term models have done a better job capturing lower dew points though the region and keep surface winds easterly through the overnight hours. These winds will keep reinforcing the middle to upper 40 dew points currently in the area. Mid-lvl clouds will gradually filter back into the region after midnight, and may lead to some stabilization of the diurnal temperature fall overnight.

WEDNESDAY: A generally quiet day is on tap for the region Wednesday. By mid-morning the 850mb ridge axis will slide east of the Tri- State area allowing gradual moisture advection northward by mid-day. Soundings indicate a thickening low-lvl moisture profile through the afternoon as weak warm advection passes across the Tri-State area. This may result in widely scattered very light showers through the afternoon and evening. At times by the evening, a bit of patchy drizzle could also be possible as ceilings remain quite low and there remains weak warm advection at the top of the saturated layer.

THURSDAY-FRIDAY: The most impactful weather in the next 7 days will take place Thursday night into Friday. Low-lvl moisture and weak boundary layer flow may keep clouds around the area early Thursday morning. High pressure over northern Minnesota may limit the rise in dew points early in the morning, again which may be a deviation from the NBM or at least pointed towards the 25th percentile. If we have quite a bit of cloud cover, then the persistent easterly winds may prevent temperatures from reaching the middle 70s.

Models are in strong agreement that a progressive open wave exits the Central Rockies and crosses the Dakotas Thursday night and Friday. This system will be very much like a late Fall to early Winter system, bringing strong layered frontogenesis and elevated instability into the Tri-state area after midnight. Deterministic models remain a bit variable with the northward extent of the 700mb forcing, with the GFS notably further north than other solutions. Ensemble based solutions are clustered fairly well with a corridor of heavy rain near Highway 14, but AI based ensembles of the GEFS/EC which seemed to pick up early location shifts last winter, are supporting of a track somewhere between Highway 14 and along I-90. Rainfall will be slow to leave the area on Friday, with some gusty northerly winds by the afternoon. Areas near the Missouri River and Highway 20 areas have the highest chance of seeing some sun in the afternoon though the current temperature forecast remains highly variable given track of rain.

Given the influx of moisture northward, rainfall forecast amounts could rise sharply over the 24 hr period ending mid-day Friday. Ensembles support a greater than 40% chance of more than 2" of QPF, with 95 percentile data already as high as 2.50-3" wherever this band of precipitation falls. As we begin to ingest more higher resolution data sets, we'll likely see these broad areas of high probabilities focus better, but also see those higher end values rise. With that said, the WPC "slight" risk of excessive rainfall seems warranted, with AI based outlooks suggesting higher risks may be possible if the forcing zone can be determined. This rainfall, especially as you begin to pass the 2-3" mark, could lead to some increases in local river levels, as rainfall this month has been above normal and we're beginning to see better responses in levels after rain ends.

SATURDAY-MONDAY: The weekend will remain slightly unsettled as upper troughing lingers over the Northern Rockies. Brief shortwave ridging should allow most areas to dry out on Saturday, but feature cooler than normal temperatures. An upper low then drifts slowly southeast across the Dakotas into Sunday and Monday. Initial indications suggest the greatest lift stays over the western Dakotas on Sunday with rain chances returning again by Monday.

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1201 PM CDT Tue Sep 15 2026

VFR conditions and light winds will persist into Wednesday morning. Depending on cloud cover and temperatures, patchy fog may develop in valley areas.

Mid-Upper cloud cover will increase through the morning of Wednesday as a breezy southeast wind develops.

FSD WATCHES/WARNINGS/ADVISORIES

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