textproduct: Sioux Falls

KEY MESSAGES

- Widespread rain expected into Saturday morning with very isolated thunderstorms and pockets of moderate rainfall expected especially near and east of I-29.

- A few more showers and thunderstorms may redevelop over northwest Iowa Saturday evening and early overnight. Severe weather is not expected, but brief heavy downpours can be expected if a thunderstorm develops.

- Daytime temperatures remain below normal, but should climb closer to normal tomorrow for areas west of the James River, and then on Sunday and Monday for the whole area.

UPDATE

Issued at 825 PM CDT Fri Sep 25 2026

Forecast remains on track this evening as widespread drizzle, low stratus, and lowering visibilities have settled into the Tri-State region. We're beginning to see mid-lvl lift increase at mid-evening with scattered showers along the Missouri River valley. Further south, a well defined mid-lvl area of vorticity continues to pivot northeast. The arrival of this wave will spur even more shower activity ahead through midnight, with the wave itself moving into the Tri-State area early Saturday morning. Instability remains very marginal, but could support an isolated rumble or two of thunder. Rainfall totals between 0.25" and 1" seem likely, with some potential for amounts near 1.5" in NW Iowa if we can see a bit more instability.

The more persistent rain will fall along and east of I-29 by 12Z Saturday,and exit the eastern CWA by mid-late morning. However, considerable low-lvl saturation will persist through mid-day supporting lingering drizzle. Showers may try to redevelop by late afternoon and evening as another weak mid-lvl vorticity area slides through the CWA. All-in-all, another very dreary day is anticipated.

Stratus may linger deep into Sunday as we maintain a cool easterly surface and low-lvl flow. There will be some potential for sun late in the afternoon, especially west of I-29, though not quite confident yet on saying areas further east will see daylight.

DISCUSSION

Issued at 233 PM CDT Fri Sep 25 2026

An area of showers continues to move east-northeast across the Highway 20 corridor in northwest Iowa. Some patchy drizzle will be left in its wake. Elsewhere, patchy drizzle will continue to occur as stratus remains in place across the area, though cloud ceilings have risen a bit since this morning, making the drizzle more patchy in nature. Showers look to develop along the Missouri River Valley and lift northward starting late this afternoon/early evening and continuing into the early overnight period as warm air advection increases across the area. An upper level wave will pivot into the area overnight as well, which will help increase the coverage of this activity. Plenty of moisture in place as PWATs increase to around 1.75+", highest generally near and east of I-29. On top of this, there will may be some elevated instability around 300 J/kg that could allow for isolated rumbles of thunder. This activity will gradually shift east-northeast through Saturday morning, with additional patches of drizzle likely behind these showers. In terms of rainfall amounts through tomorrow morning, we look to generally see around 0.75-1.25" near and east of I-29, with lesser amounts the farther west you go across the area. A few spots could see upwards of an 1.5-2" (20-30% chance) if multiple pockets of heavy rain move over one area. But with training convection not expected, flash flooding concerns remain very low.

Will have to watch Saturday afternoon and evening as a secondary area of mid level vorticity moves across the area. There may be enough daytime heating near and west of I-29 to allow for around 500-750+ J/kg of CAPE to develop. There is a warm layer around 700 mb that any rising parcels will have to fight against before a thunderstorm could develop, but the lift provided by the upper wave may be enough to overcome it, especially closer to I-29 where this warm layer is a little weaker according to soundings. Should it break the cap, a few thunderstorms may be able to develop. Severe weather is not expected as weak shear will be in place. So lightning and brief heavy downpours would be the main threat if any of this development were to occur (20% chance). Might be a better chance (30-40%) of this development over northwest Iowa Saturday evening as an 850 mb front moves into the area. Slightly better shear around 20 kts will be place at that time, so perhaps a more organized storm is possible, but still not enough for a severe weather concern.

This 850 mb front will bring a very brief period of northerly winds overnight Saturday into Sunday, which may help thin the stratus a little bit. But then fog will likely develop as ample moisture near and at the surface will be still be present. Any fog and stratus will linger into Sunday morning, but any stratus is looking more shallow than what we've seen compared to the past couple of days so drizzle appears unlikely. With the more shallow stratus in place, should be able to mix out some of it Sunday afternoon, allowing for a few periods of sunshine and warmer temperatures, with highs in the upper 60s to lower 70s. This period of drier weather will likely be brief though, because our next storm system is set to move into the area Monday night into Tuesday. Latest LREF probabilities for this time period shows around a 20-30% chance of at least an inch of rain mainly south of I-90.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1056 PM CDT Fri Sep 25 2026

Drizzle, fog, and scattered showers continue to develop late this evening. A larger system will begin to track northward into the Tri-State area after midnight bringing periods of moderate rain and isolated thunderstorms into Saturday morning. Visibility at times may range from 1-4SM with rain, with ceilings dropping near or below 500 ft at times.

The majority of rain will continue to lift northeast and into south central Minnesota by mid-morning, but signs continue to point to occasional drizzle lingering until mid-day.

After a brief period where ceilings and visibility may improve near to above 1000 ft AGL, scattered showers, drizzle, or fog could reform by Saturday evening.

FSD WATCHES/WARNINGS/ADVISORIES

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