textproduct: Sioux Falls

KEY MESSAGES

- Scattered light rain and sprinkles move in around daybreak and gradually dissipate by mid-day. Precipitation amounts will be light with a slow temperature recovery towards 70 degrees in the afternoon.

- Scattered rain and non-severe thunderstorms arrive by daybreak Monday. A brief, localized, and conditional risk for severe storms develops Monday afternoon in NW Iowa and NE Nebraska.

- Near normal temperatures for the rest of the week with increasing rain chances during the second half of the week.

UPDATE

Issued at 355 AM CDT Sun Sep 13 2026

Taking a look across the area, the focus continues to be on a developing area of ACCAS across central and southcentral SD this morning. Current thinking is as a weak shortwave intersects this growing cloud deck, should see developing showers gradually become more widespread across our area from daybreak to mid-morning with the strengthening frontal forcing. While accumulations should be light, can't rule out a few pockets of moderate rainfall. Nonetheless, should see most of this activity exit our area closer to late morning. Otherwise, another cool day is ahead with highs mainly in the upper 60s to low 70s. Heading into Monday, the forecast remains on track with more widespread rain chances on the docket.

We'll likely see two rounds of activity: 1. With the lifting warm front around daybreak and 2. with the cold front and LLJ from late morning to early evening. There could be a brief break between rounds. While the focus will be mainly on locally heavy rainfall, there is still a highly conditional severe risk possible across northwestern IA during the evening hours. The main question we have is if we can sufficiently recover after the morning activity to destabilize. Given the uncertainty with surface temperatures and how poorly guidance usually handles stratus and lower clouds, my gut says we'll likely keep the stratus longer than expected lowering our potential for any stronger activity in the evening. Lastly, should see most of this activity clear out by late evening.

DISCUSSION

Issued at 106 PM CDT Sat Sep 12 2026

THIS AFTERNOON: A perfect early fall Saturday across the region as any lingering sprinkles to showers have move away from the area. Quiet conditions will continue into the evening with winds eventually turning light and variable after 00Z.

TONIGHT: Temperatures will fall quickly this evening towards the 40s before upper and then mid-lvl clouds increase after midnight. The settling of a mid-lvl trough into the Dakotas will increase mid- lvl dPVA but also layered frontogenesis focused at the 850 mb level near and south of the Missouri River and 700:600 mb frontogenesis near or north of Highway 14. CAMs and some lower resolution guidance struggling on the placement of this lift, leading to a higher than typical spread in PoPs by time lift is maximized near or after daybreak. High cloud bases will keep QPF light.

SUNDAY: Morning light sprinkles/rain will persist at times through the morning focused in or or two narrowing bands. As the vorticity passes east late in the morning, we should see this activity dissipate, but leave a lingering mid-lvl cloud field in the area. Temperatures will recover slowly in the afternoon, but may struggle to reach the 70 degree mark.

SUNDAY NIGHT-MONDAY: Shortwave ridging moving through the Plains early Sunday evening and early in the overnight hours will keep skies clear allowing for another quick temperature fall. After midnight hours, models remain in good agreement that troughing arriving into the Western High Plains will induce a 40 knot LLJ through central South Dakota and Nebraska. Convergence on this LLJ will spark scattered convection that may arrive into the Missouri River valley communities by 12Z. This non-severe convection continues to lift northeast Monday morning with most of the focus before 18Z. Given the orientation of the LLJ lingering and persistent showers may continue in the afternoon. My big concern on Monday may be with temperatures given ongoing cloud debris into the afternoon. Latest NBM 25/75th percentile spread suggests 7-12 degree temperature variance, with the 10/90th spread as high as 17 degrees. While we certainly could see highs in the middle to upper 70s, clouds could also hold us considerably lower.

Severe weather risks Monday afternoon remain focused in only the very far portions of the CWA where there may be potential for a warm front to lift northward. Greatest potential remains focused across northeast Nebraska and northwest Iowa from 3pm to 7pm. It's also very possible that continued convective debris really prevents any meaning warming to arrive and limits the risk further south.

TUESDAY-SATURDAY: We'll remain on the cool side of the baroclinic zone for the remainder of the work week. With mid-lvl flow remaining westerly, this will present fewer opportunities for any large scale surge of warm air northward. Both limiting high temperatures to the upper 60s to lower 70s (near seasonal normals), but also keeping severe weather risks minimal. Medium range ensembles hint at two timeframes of focus for rainfall focused around Wednesday (lighter amounts), and then late Thursday and Friday where stronger synoptic lift enters the Plains and forces more abundant low-lvl moisture northward. Ensembles have been trending the probabilities for >0.25" higher each model run and this trend may continue based on the 12Z data.

AVIATION /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1246 AM CDT Sun Sep 13 2026

Scattered showers will begin to develop and increase in coverage towards the daylight hours this morning and spread from west to east. Though a few brief pockets of MVFR visibilities will be possible in the few more robust showers that can develop, VFR conditions are expected for most of the area. The exception will be along the Highway 20 corridor including KSUX where a few thunderstorms will be possible during the morning hours. All this activity pushes east of the area this afternoon, with the next round of rain likely not occurring until shortly after the end of this period.

Winds will be light and variable through the early morning hours, with winds gradually picking up out of the east-southeast through the daytime hours today. Strongest winds through the period will be over south-central South Dakota where winds could gust to 25 kts this afternoon and evening. These stronger southeasterly winds will begin to push eastward across the area also just after the period ends.

FSD WATCHES/WARNINGS/ADVISORIES

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