textproduct: Sioux Falls

KEY MESSAGES

- Showers and isolated thunderstorms continue into Saturday morning, especially east of the James River. Locally heavy rain and lightning are the main threats.

- Outside of showers, drizzle and fog are expected into mid Saturday morning. Fog is most likely west of the James River.

- Additional scattered showers and isolated storms Saturday night into early Sunday.

- More widespread rain returns later Sunday night into Monday night. Moderate to high (60 to 90%) chance for more than an inch of rain. Flooding is unlikely, but not zero. Additional rainfall is likely on Tuesday.

- A low confidence threat for low topped supercells Monday afternoon and evening in far southeast SD, northeast NE and northwest IA.

UPDATE

Issued at 316 AM CDT Sat Oct 31 2026

Somewhat busy start to Halloween weather-wise. Showers and storms continue trekking northeast, mainly near and north of I-90 at the time of this discussion. Still enough elevated instability to see a fair amount of lightning but severe weather is not expected. Precipitation is moving relatively slowly and with locally moderate to heavy rain, rainfall amounts since midnight are over an inch near and north of Sioux Falls with more widespread 0.25" to 0.50" observations. Flash flooding is not expected, but could see some localized ponding of water for areas. Additional showers/storms are moving north across northern NE and IA.

Further west toward the James River, showers are much more isolated. Light winds have allowed fog to develop, with some dense fog across south central and central SD. This should dissipate by mid morning.

No significant changes to the forecast outside of refining pops for the next few hours. Expect a break in the rain through at least early afternoon. However, a couple of short waves begin moving north through the afternoon/evening, which brings the return of rain and isolated storm chances. Elevated instability remains weak (a couple hundred Joules) so lightning would be the main concern. Chances increase from south to north tonight.

Still quite a bit of variance toward early next week with regards to the surface low. Looking at 00z Tuesday (6 PM CST Monday), the 31.00z NAM is the furthest south (northeastern NE) and the GFS is the furthest north (US Hwy 14) with the ECMWF and Canadian both elsewhere in southeastern SD. Still have to keep an eye on the potential for a few stronger storms. See the Discussion for more details.

DISCUSSION

Issued at 148 PM CDT Fri Oct 30 2026

Showers remain likely tonight into Saturday morning as low level moisture deepens, roughly the lowest 5 km, and marginally dry, cooler air above this layer allows for weak instability, generally 200-500 J/kg CAPE. This should generate mainly showers, but a few lightning strikes will be possible. Rainfall amounts will mostly be light, but some pockets of a tenth of two will be possible.

Saturday night into Sunday should be mostly dry, but moist neutral soundings and lingering moisture/cloud cover may allow for some patchy drizzle and showers. Overall low impact, but likely not an entirely dry period.

A fairly well agreed upon trough of low pressure will move onto the Plains Sunday night, deepening on Monday as a strong southern stream jet strengthens. This should provide that area with widespread rainfall and if everything comes together timingwise, the threat for an isolated tornado over southeast parts of the area.

All models continue to indicate a widespread 1-2" of rainfall from Sunday night into Tuesday morning. Very little disagreement for the most part on timing and location of the rainfall. Given a fairly wet pattern the past 6 weeks or so river flooding could start to become a problem. But for now, the latest hydrologic modeling suggests at least 2.5-4" of rain would be needed to push rivers to action stage and minor flooding, so for now chances of river flooding are pretty low (<20 percent). Also suggestions that 1.5" of rain in an hour could produce some localized flash flooding, but for now the rainfall rates should not be quite that high. All in all, it looks like a band of warm advection rainfall will lift northward Sunday night into Monday. Later Monday afternoon into Monday night a dry slot could move in and if convection does not develop, a dry period or period of drizzle will be possible. Then later Monday night into Tuesday wrap around rainfall will move through.

While this is a very low threat probability, we will need to keep an eye on the development of surface low pressure Monday afternoon as the upper level wave moves through. Starting to see indications this surface low pressure could end up near southeast SD/northwest IA which could bring about a threat for some low topped supercells/isolated tornadoes. The 6z ensemble data has the EC placing this SFC low in southeast SD late Monday afternoon while the GEFS and Canadian Ensemble are in eastern NE. Obviously a big difference so trends will need to be monitored. The 12z GFS is now placing the surface low in southeast SD late Monday afternoon as well.

Tuesday will likely see some wrap around rainfall continue, but should diminish throughout the day. Wednesday through Friday should be mostly dry and cooler with highs from the upper 40s to mid 50s.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 638 AM CDT Sat Oct 31 2026

MVFR and lower stratus expected through much of the period. Scattered showers and isolated thunderstorms continue through mid to late morning, moving northeast over the area. Seeing some visibility at or below 2 SM at times with locally heavier rain and TS. Additionally, fog west of the James River is leading to reduced visibility, including some visibility below 1 SM. Fog lifts mid to late morning.

May see some VFR stratus at times, but overall MVFR or lower conditions expected. Rain showers return this evening into tonight, but confidence is low on timing/coverage, so kept PROB30 groups at all sites.

South to southeast winds increase late this morning with gusts around 20 knots into the evening, strongest west of I-29. Winds taper down tonight.

FSD WATCHES/WARNINGS/ADVISORIES

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