textproduct: Sioux Falls

KEY MESSAGES

- Areas of drizzle may result in occasional minor drops in visibility into the morning.

- The next better chance for rain will come tonight into Monday. Thunderstorms will be very isolated and severe weather is not expected, but localized rainfall totals in excess of an inch are possible.

- Below normal temperatures will persist through next week.

UPDATE

Issued at 430 AM CDT Sun Sep 20 2026

Northeast flow has become a bit more mixy beneath the stratus layer early this morning, which has allowed for improvement in visibility and slow increase in cloud base heights. While this will limit extent of fog through the remainder of the night, weak lift atop a deep stratus deck is still producing areas of drizzle based on web cam imagery and spotty Trace-0.01" precip amounts on area METARs. Expect the potential for light drizzle to continue into the mid-late morning when this lift diminishes. However, broader lift and even a shallow convective layer below 850MB will bring increasing chances for light rain to portions of southeast SD into northwest IA by mid-late afternoon.

Rain coverage is then expected to increase through tonight as a broad mid-upper level wave slowly spins eastward across the region. HREF LPMM (Localized Probability-Matched Mean) indicates a potential for a band of heavier rainfall, upwards of an inch to locally over 2 inches. While the location is still somewhat uncertain, trends favor this band extending from portions of the I-90 corridor in southeast SD, into the Highway 18 corridor in northwest IA. Latest NBM has caught on to this and has begun trending QPF amounts upward from previous runs, though still falling shy of an inch most locations. This may need to be refined further by later shifts.

Otherwise, a cool and breezy day is on tap with highs mostly in the lower 60s and northeast winds gusting near 25 mph at times today.

DISCUSSION

Issued at 1247 PM CDT Sat Sep 19 2026

The low levels remain saturated to near saturated tonight into Sunday morning which will keep the potential for fog in place, as well as patchy drizzle. Dense fog will again be fairly sparse, but some locations will see the visibility fall to a half mile or less at times.

Overall, Sunday looks to be a pretty dreary day with low level saturation deepening through the day. While the visibilities will likely improve a bit through the morning, stratus will remain fairly low and will not dissipate. As this low level moisture deepens, a weak wave will approach from the south and bring slightly cooler temperatures aloft and a bit more elevated moisture. This should allow for scattered showers to develop, but with only very weak instability thunder looks unlikely. As this wave rotates northward, a slightly stronger wave will move eastward through northern NE into northwest IA which should keep an expanding area of rain in place across the area. Given the placement of the upper level wave and the associated instability, parts of south central and southeast SD down the Missouri River will likely see the better chances for an inch or so of rain. The 12z Nam, RRFS and HRRR all paint these higher rainfall amounts near and south of I-90.

This wave slowly moves through on Monday, so expect to see showers slowly dissipate from west to east through late afternoon. Stratus will once again be difficult to shake as the push behind this wave is pretty weak and lighter northeast to east flow will be in place in the lower levels. Some hints in the soundings that clearing will be possible on Monday night, but with light winds and a moist boundary layer, fog will then become moire likely for late Monday night into Tuesday morning.

Tuesday and Wednesday will see some weak upper level ridging with afternoon temperatures likely only rising into the 60s.

Wednesday night into Thursday a trough of low pressure will approach from the west and bring a chance for showers and isolated thunderstorms. Severe weather looks unlikely. For now the better chances will likely be west of I-29.

Temperatures should remain a touch below normal Thursday into Friday with some potential for spotty showers. Highs generally in the upper 60s to lower 70s.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 640 AM CDT Sun Sep 20 2026

IFR-MVFR ceilings will persist through the period, though brief breaks near Highway 14/KHON are possible early in the period. Widespread visibility restrictions are not expected, but areas of light drizzle this morning may result in brief MVFR visibility at times. Rain will spread over the region from the southwest this afternoon and tonight. This again may result in MVFR visibility at times, though confidence is not high enough to include sub-6SM visibility in TAFs at this time.

FSD WATCHES/WARNINGS/ADVISORIES

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