textproduct: Sioux Falls

KEY MESSAGES

- Rainfall overspreads most of the area through tonight, gradually ending west to east on Monday.

- Rainfall amounts will average about 0.50" to 1.50" in most locations.

- Below normal temperatures will persist through next week, but gradually become more mild late in the week.

DISCUSSION

Issued at 141 PM CDT Sun Sep 20 2026

Patchy drizzle remains possible late this afternoon into the evening ahead of the incoming rainfall. The rain will move into the area through the afternoon into tonight. Low pressure to the southwest will swing saturation and lift aloft into the area this afternoon with a dry slot working north towards the Missouri River. This seems to suggest that the better potential for a more steady rainfall will be closer to I-90 as the dendritic layer dries out south of I-90 during the evening, but remains saturated near and north of I-90. Model soundings do hint at some weak instability near the Missouri River which may help overcome the lack of saturation in the dendritic layer during the evening and overnight hours, but the rainfall would be more scattered in nature. If this weak instability does not come to fruition, drizzle will be more likely towards the Missouri River. Given how weak any expected instability will be, thunderstorms are not expected.

As for amounts through tomorrow, model agreement is fairly high in a swath of a half an inch to an inch and a half, focused near I-90 in southeast SD, then east into northern parts of northwest IA. These rainfall amounts are not expected to cause any flash flooding or rapid rises along rivers.

Monday will see lingering showers across the area, with a more focused area over northwest IA as the upper level low slowly moves out of the area. Amounts will be lower through the day on Monday, but parts of northwest IA could see a quarter inch of additional rainfall. Otherwise Monday will be cool and cloudy with highs from the upper 50s to mid 60s.

Monday night into Tuesday morning could see some fog with light southeast flow and a fairly moist boundary layer.

Tuesday and Wednesday should both be dry and cool with highs in the 60s both days. Winds will increase on Wednesday with gusts around 30 mph possible near and west of the James RIver.

Wednesday night into Thursday will be the next better chance for showers and thunderstorms. At this time severe weather and heavy rain look unlikely.

Temperatures will rebound back to around normal Friday into next weekend as westerly flow aloft develops. Periodic chances for showers and thunderstorms are expected during this time.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1149 AM CDT Sun Sep 20 2026

Widespread MVFR and IFR conditions are expected through the period. From about 18z to 21z, ares north of I-90 may see periods of VFR conditions as the cumulus field breaks up and then reforms. Patchy drizzle remains likely over mainly northwest IA before afternoon mixing helps dissipate much of this activity. Rain will develop across the area with the most persistent rain likely closer to I-90 and then into northwest IA this evening into Monday morning. Closer to the Missouri River rain may lighten, but then drizzle will become more likely later tonight into Monday morning.

FSD WATCHES/WARNINGS/ADVISORIES

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