textproduct: Sioux Falls

KEY MESSAGES

- Rain chances increase through the night tonight, with very isolated thunderstorms and pockets of moderate rainfall expected especially near and east of I-29. Flash flooding is unlikely.

- 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.

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 /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1248 PM CDT Fri Sep 25 2026

MVFR and IFR stratus persists across the area to start the period. Further lowering of the cigs to LIFR conditions is once again expected late tonight and into early tomorrow morning before improving again by the mid to late morning Saturday.

Patchy drizzle will remain in place this afternoon, with scattered showers developing this evening and increasing in coverage overnight. Very isolated thunderstorms look to be embedded within this activity, with enough confidence in this potential to at least add a PROB30 group to KSUX tonight for TSRA.

Winds will be out of the southeast through the period, remaining on the marginally breezy side through tomorrow morning with sustained winds around 10-15 kts with isolated gusts up to 25 kts possible.

FSD WATCHES/WARNINGS/ADVISORIES

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