textproduct: Sioux Falls

KEY MESSAGES

- Isolated showers on Thursday could produce wind gusts of 40 to 50 mph. A similar story may develop Friday afternoon as well.

- More widespread rain risks return late Saturday into Sunday, though considerable uncertainty remains on the track of this system.

- Greatest severe weather risks continue to remain focused south of the Missouri River and Highway 20 corridor Saturday.

- Forecast rainfall totals vary significantly through Sunday, though greatest potential for excessive rainfall remains just south of the forecast area. Ensemble probabilities for >1.0" are around 30-40%.

UPDATE

Issued at 245 AM CDT Thu Jun 18 2026

No major changes made to the short term portions of the forecast. Mid-lvl clouds continue to filter southward, meanwhile mid-lvl frontal zone will keep overcast skies along the MO river and Highway 20 corridor. Some patchy fog may still be possible, but should be very localized.

Afternoon showers and isolated thunderstorms may develop in areas along and especially east of I-29 this afternoon. Synoptic winds will be much weaker than Wednesday, so any localized gusts in convection will stay below severe limits.

DISCUSSION

Issued at 144 PM CDT Wed Jun 17 2026

A strong jet max continues to wrap around the south side of an upper level low, bringing strong winds to the area. Peak mixing suggests that wind gusts could approach 50 mph. Model soundings also indicate some weaker surface based instability this afternoon, which will likely generate scattered showers and isolated thunderstorms. The main concerns from any of this activity will be the potential to mix down even stronger winds, possibly 60 to 65 mph. These stronger winds will remain much more isolated.

Thursday will see deep, but weakening northwest flow across the area. We will likely see a threat for isolated showers with locally gusty winds to 40 mph as surface based peak mixing CAPE climbs to about 200 J/kg.

Thursday night into Friday a weak wave will approach and bring some elevated moisture return and very weak instability. For now any impacts from this will be very minor.

The next system of interest will come Saturday, but with some differences from model to model. The 6z EC Ensemble is bringing a 20- 30 percent chance for 2+" of rain to around the Missouri River into parts of northwest IA while the 12z GFS ensemble and 12z Canadian ensemble leave these better chances farther south and closer to I- 80. Classically the heavier rain many times falls between roughly the surface to 850 mb boundary and for now that remains south of the area, but will need to be monitored in case it drifts north. Regardless, flooding potential is fairly low as rainfall has been spotty at best lately.

Below normal temperatures and periodic chances for showers and thunderstorms are expected Monday through Wednesday next week. A few shortwaves are expected to move through, with slightly better chances Monday and Wednesday.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 556 AM CDT Thu Jun 18 2026

VFR conditions will persist for much of the upcoming 24 hour TAF period. Scattered to broken mid-high level cloud cover persists to mid-day when CU field will begin to develop. An isolated shower or thunderstorm may form this afternoon, but coverage may be too limited for any mention in this TAF set. Winds may gust up to 20 knots at times this afternoon.

Skies clear with the loss of heating and will remain VFR into Friday morning. With light and variable winds, may have to watch for daybreak shallow fog.

FSD WATCHES/WARNINGS/ADVISORIES

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