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 /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 651 PM CDT Sun Sep 20 2026

A few breaks in the MVFR/IFR stratus are out there to start the period, but expect cigs to lower again in these areas as the evening progresses. We'll continue to see this low stratus continue into the day on Monday, with drizzle likely at times especially near the Missouri River Valley. Overnight tonight we will also see some showers with locally moderate rainfall especially around and between the I-90 and Highway-18 corridors. Storms remains unlikely, though a rogue rumble of thunder cannot be ruled out (<10% chance). Showers will very slowly drift southeastward through the day on Monday. Winds will be mainly out of the east-northeast through the period, around 5-10 kts. Some of the heavier showers may be able to mix down a wind gust to around 20 kts overnight tonight.

FSD WATCHES/WARNINGS/ADVISORIES

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