textproduct: Sioux Falls

KEY MESSAGES

- Isolated sprinkles remain possible through the afternoon and early evening, with patchy drizzle possible again by early Monday morning.

- Rain and a few thunderstorms are likely (70-90+%) late Monday night and into Tuesday. Pockets of heavier rainfall will again be the primary concern as severe weather appears unlikely.

- Additional rain may impacts areas especially south of I-90 through the day on Thursday. Prolonged rainfall on top of recent rainfall could lead to some flooding concerns. Keep up to date with the latest forecast.

DISCUSSION

Issued at 249 PM CDT Sun Sep 27 2026

Finally starting to see some stratus eroding and leading to some sunshine in parts of the area this afternoon. We may continue to see some erosion of the stratus so long as the sun is up as the relatively high sun angle (at least compared to winter) seems to be able to thin some of these lower clouds. Soundings still show some shallow instability within the lower cloud layer though, so we may continue to see some sprinkles to very light showers develop mainly through the afternoon and early evening. A few returns have popped up on radar west of the James River, but the lack of droplets on area cameras supports the idea that any rain will be very light in nature.

Stratus should build back in through the overnight hours along with some more fog. Not expecting fog to be as widespread or as dense as it was earlier this morning, but still locally dense fog will be possible mainly near and east of I-29 as this is where winds will be lightest. Models are a bit split on how shallow this stratus that develops tonight will be, so there remains some uncertainty as to if there will be some drizzle or not tomorrow morning. Enough confidence to mention at least some patchy drizzle during the morning commute so you may have to deal with some drizzle on your way to work or school. Temperatures will once again be slow to fall off through the overnight hours, especially after the low clouds redevelop and thicken late tonight. Think most of us will end up in the lower 60s for morning lows, though some pockets of upper 50s will be possible mainly near and east of I-29. Lowered the NBM a bit by blending in some CONSAll to minimum temperatures given the returning southerly flow expected overnight.

Monday is looking to be a similar day to today. We'll start off with some low stratus that will gradually become more shallow into the early afternoon. At the same, there will once again be a shallow layer of instability to allow for some more sprinkles or light rain showers especially into the afternoon hours. At the same time, a trough will be digging towards the Desert Southwest and send an initial area of vorticity into the Northern Plains through the day. This should keep the more organized rain showers and thunderstorms tomorrow north of the area, though can't rule out some of this activity clipping our far western areas depending on the ultimate track of the wave. If this activity were to clip the area, thunderstorms appear unlikely as any parcels that rise will only have access to decent instability if it could overcome a strong cap around the 850/700 mb layer, which appears unlikely with the better forcing expected to our north and west. Also similar to today, most high temperatures will be in the upper-60s to lower-70s, perhaps slightly warmer west of the James.

The aforementioned Desert Southwest trough will send another upper wave into the region Monday night into Tuesday, this time much closer to home. With that, rain and storms are expected (70-90+%) especially late Monday night into the day on Tuesday. Modest shear will be in place, but instability looks fairly weak and so severe weather looks unlikely. Heavy rain appears to be the main threat with this system, especially when looking a bit ahead as the main trough closes off and absorbs the remnants of Hurricane Polo and very slowly moves eastward. This will mean that the trough continues to send upper waves into our region and so higher rain chances may continue especially south of I-90 through the day on Wednesday and potentially as late as into Thursday morning. Based on the position of the trough/closed upper low, the better instability will likely stay south of the area. So instead of any convectively driven flooding concerns, will have to watch how rivers respond to prolonged rain on top of the rain we've already seen this past week. The latest excessive rainfall outlooks from the WPC paint the southeastern half of the area with level 2 of 4 Slight Risks for Tuesday and Wednesday, so continue to monitor the forecasts for the latest information.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1257 PM CDT Sun Sep 27 2026

Any lingering fog will lift over the next hour or so across the area, though MVFR to IFR cigs are still present for most locations to start the period. We will see cigs rise through the afternoon along with some scattering out of the lowest layer of the stratus, which will bring the return of VFR conditions to parts of the area. At the same time, a few sprinkles to light showers will remain possible through the early evening hours. We'll see cigs drop again tonight along with some patchy drizzle especially near and east of I-29 by early tomorrow morning. Patchy fog is also expected in spots, but it shouldn't be as widespread as we saw earlier this morning.

Winds will be light out of the east-northeast through the afternoon, gradually turning east and then southeast heading into the day tomorrow. Winds will begin to increase near and west of I-29 tomorrow morning, with gusts to around 25 kts possible near and west of James River by the end of the period.

FSD WATCHES/WARNINGS/ADVISORIES

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