textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers, sprinkles, or drizzle will develop from early afternoon into the evening mainly along and east of I-29.

- 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.

- Areas of locally dense fog could develop tonight mainly across northwestern IA. Be prepared for temporary reductions in visiblity on the Thursday morning commute.

UPDATE

Issued at 335 AM CDT Wed Sep 16 2026

Taking a look across the area, mostly clear conditions continue across most of the area as a surface high continues to push east this morning. With light and variable surface winds, can't rule out some patchy valley fog along our water ways and low lying areas. However, not expecting any widespread development mainly due to slightly large dew point depression. Either way, should any lingering fog dissipate just after daybreak. Otherwise, mostly clear conditions will give way to overcast skies by early afternoon as another weak mid-level wave drifts across the area. Scattered showers will be possible mainly east of I-29 with perhaps a rumble of thunder or two. From here, the focus turns towards the later parts of the week as a stronger wave lifts out of the Colorado Rockies into western SD and NE. Initial development will likely take place along the Missouri River Valley as a ribbon of vorticity lifts northeastwards during the second half of Thursday.

However, the main course will start Thursday night as the warm air advection regime strengthens ahead of a developing surface/850mb low. With this and strengthening LLJ in place, showers and thunderstorms likely develop across the Black Hills and lift northeastwards during the night into central and southeastern SD. While the severe weather risk is low, locally heavy rainfall will be the main threat as PWATs approach the top 1% to Max of ensemble guidance. Even through there are still some lingering questions about where the axis of heaviest precipitation sets up, we've continued to see a northeast shift in the heaviest amounts with the latest runs of guidance. This shift is also echoed in the ensemble guidance with both the GEFS/GEPS showing moderate to high confidence (40%-70%) in 0.50" or greater of QPF along and north of I-90 with the highest confidence along U.S. Highway-14 corridor. Either way, the wettest conditions are expected from Thursday night into the day on Friday with most of this activity tapering east by late Friday night into Saturday morning.

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 through 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 /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 638 AM CDT Wed Sep 16 2026

Mainly VFR conditions during the day will transition to MVFR and lower overnight. Should see cloud cover begin to build in by the second half of the day with a few scattered showers/sprinkles. MVFR to IFR cigs moving in from the south behind that activity. Cloud bases should continue to lower overnight as dew point depressions shrink. After 06z, areas of stratus will begin to act as fog mainly across northwestern IA promoting IFR to LIFR cigs and vsbys. Otherwise, light southeasterly winds will become more light and variable overnight.

FSD WATCHES/WARNINGS/ADVISORIES

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