textproduct: Sioux Falls

KEY MESSAGES

- Dense fog becoming more widespread near and west of the James River Valley early this morning, with patchy dense fog in the higher elevations farther east across the Coteau des Prairies and Buffalo Ridge.

- Spotty showers/drizzle continue early this morning near and east of I-29. Coverage should continue to decrease, but low level moisture may continue to produce isolated sprinkles or drizzle through tonight.

- Greater chances for showers and a few thunderstorms Monday night into Tuesday. Pockets of heavier rainfall will again be the primary concern.

UPDATE

Issued at 320 AM CDT Sun Sep 27 2026

Stratus has gradually thinned/cleared across western portions of the forecast area overnight, but any clearing quickly allows fog to develop in its place. Already issued a Dense Fog Advisory for much of the western CWA and will continue to monitor for possible expansion through the pre-dawn hours.

Meanwhile, eastern portions of the area currently remain under a thicker stratus deck, though patches of clearing have been noted in portions of far southeast SD. Still seeing signs of light rain or drizzle in portions of southwest Minnesota/northwest Iowa, so have increased pops a bit for the next 2-3 hours as the subtle wave slowly exits the area. Cannot rule out lingering very light drizzle beneath any thicker stratus this morning, with a shallow convective layer beneath a strong inversion and additional mid level instability potentially producing spotty sprinkles/light showers across the area this afternoon into the early evening.

Unfortunately, some forecast soundings indicate another round of thicker stratus developing late tonight into Monday morning with a potential for another drizzly start to the work week. This does not seem an unreasonable solution as a persistent southeast flow does not bring a strong dry push into the area. Confidence is not high enough to introduce the drizzle into Monday morning just yet, but will be something to consider in later forecasts.

DISCUSSION

Issued at 257 PM CDT Sat Sep 26 2026

The area of steady moderate rain that impacted the area this morning is exiting off to our northeast; however, patchy drizzle continues and will continue on and off through the afternoon where clouds ceilings are lowest, which is generally from far eastern South Dakota into southwest Minnesota. Farther west, we've seen some breaks in the lowest clouds, allowing for some destabilization to occur. Up to 500-1,000 J/kg of MLCAPE has developed per latest SPC Mesoanalysis along the Missouri River Valley, and as a secondary mid level wave moves across the area, a few weak thunderstorms have already developed over northern Nebraska and are lifting northward. Severe weather is not expected given weak shear across the area, but we will likely continue to see some additional showers and isolated thunderstorms develop through the afternoon and evening. The best chance of rain (30-60%) with this activity will be over western Iowa, far northeast Nebraska, and far southeast South Dakota, stretching to far southern Minnesota by the late night hours. Tall, skinny CAPE profiles and deep warm cloud layers suggest heavy rain will be the primary threat with any thunderstorm. This could lead to a few pockets of ponding in low- lying and poor drainage areas, but flash flooding is unlikely.

Heading into tonight, the areas that saw some clearing stratus (primarily near and west of the James River) will see some fog develop, meanwhile the stratus deck elsewhere is expected to lower through the night and become fog. Locally dense fog is likely given all the near surface moisture, though coverage and exact locations where the densest fog will reside precludes a need for a Dense Fog Advisory at this time, but trends will be monitored. This fog will gradually lift through the mid morning hours, but likely become low stratus heading into much of the day on Sunday. Still the potential for some of this stratus to mix out a bit and allow for brief breaks of sun mainly near and west of the James River, but this will likely be the exception, not the norm across the area. Some instability in the low cloud layer may allow for a few sprinkles to spits of drizzle, but it's not looking as persistent as it has been the past couple of days.

Heading into early next week, a trough over the West Coast will begin to dig into the Desert Southwest. Ahead of this, an upper wave will move into the area late Monday into the day on Tuesday and bring our next round of rain and storms to the area. Latest GEFS shows around a 30-40% chance of at least an inch of rain mainly focused over northwest Iowa and adjacent areas. This is a bit higher than other guidance, but appears to be the most reasonable at this time given ensemble PWATs show anomalies nearly of +1" in place as this system moves through. The aforementioned trough over the Desert Southwest will absorb the remnants of a Pacific Ocean tropical cyclone as it ejects to the north and east during the middle to end of the next work. This may help to keep a decent amount of moisture in place over primarily northwestern Iowa into the end of the upcoming work week, though at this point it looks like the heaviest rain associated with this will stay south of the area.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 645 AM CDT Sun Sep 27 2026

Widespread LIFR-VLIFR conditions at the start of this period, with dense fog roughly west through north of a KYKN-KFSD-KMWM line and persistent low stratus throughout the region. Overall the visibility should improve to VFR or lower end MVFR range by 15Z-17Z as fog diminishes and stratus slowly lifts. Areas of drizzle may again accompany the fog/low stratus this morning, but precipitation amounts are expected to be much lighter than recent days.

Ceilings should likewise slowly rise into MVFR to locally VFR categories this afternoon, and a shallow unstable layer may allow spotty light showers/sprinkles to develop during the afternoon to evening. Thunder is not expected at this time.

Low confidence toward the end of this TAF period, but some model solutions point to a potential repeat of lowering ceilings and perhaps patchy drizzle again developing after 28/06Z. Did not introduce any sub-MVFR ceilings or drizzle at this time, but later shifts will monitor potential and introduce if needed.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until 10 AM CDT this morning for SDZ038>040- 050-052>060-063>065-068. MN...Dense Fog Advisory until 10 AM CDT this morning for MNZ071-072- 080-097. IA...None. NE...None.