textproduct: Sioux Falls

KEY MESSAGES

- Widespread rain/drizzle expected this morning with pockets of moderate rainfall, especially near and east of I-29. Thunder risks are low, but could occur with a heavier shower.

- Additional showers or storms may redevelop in northwest Iowa late this afternoon into the 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.

- After a brief break late Sunday into Monday, rain chances return Monday night into Tuesday. Pockets of heavier rainfall will again be the primary concern.

UPDATE

Issued at 415 AM CDT Sat Sep 26 2026

Light to moderate showers located mainly east of the James River as of 330 AM will slowly track east-northeast across the forecast area through the morning. Could continue to see areas of drizzle on the western edge of the rain, but with decreasing lift behind the departing lead wave, drizzle coverage should likewise diminish as we move toward midday-early afternoon. Any break from the rain will be brief, especially in our eastern areas as a trailing wave quickly slides across the region this evening. This stronger wave could trigger a few thunderstorms with heavier rainfall rates. However, severe weather risks are very low given lack of shear and limited instability.

Stratus looks to remain persistent through tonight into Sunday morning, with increased probabilities of fog later tonight into Sunday morning as well. May see some breaks in the stratus by Sunday afternoon, especially west of I-29 as the low level moist layer thins a bit. However, with a continued moist east-northeast flow, confidence is low regarding how far east any appreciable sunshine will be seen and have generally trended higher than the NBM in projected sky cover into Sunday.

Another system looks to move across the region later Monday into Tuesday next week. Again, limited instability and shear will keep severe weather risks low, but pockets of heavier rainfall will be possible.

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 /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 635 AM CDT Sat Sep 26 2026

Rain and/or drizzle blanketing much of the area at the start of this TAF period will slowly move east through midday. IFR-LIFR ceilings will again be prevalent with this activity, along with occasional MVFR visibility. Ceilings may briefly improve to the lower end of MVFR range (below 2kft AGL) this afternoon, with a potential for VFR conditions toward central South Dakota (west of KHON-KMHE). However, ceilings again deteriorate into the IFR-LIFR range after 27/06Z with an increased potential for IFR or lower visibility in BR (scattered VLIFR in FG).

This evening will also bring a low chance for thunderstorms to portions of northwest Iowa, but confidence in occurrence is too low to include TS at KSUX at this time.

FSD WATCHES/WARNINGS/ADVISORIES

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