textproduct: Sioux Falls

KEY MESSAGES

- Low stratus and fog, including locally dense fog, continue into mid morning. Fog should lift by 10 AM. Lower confidence for stratus and fog Sunday morning and again Monday morning.

- Scattered showers and a few storms are expected this afternoon especially near and east of I-29. Locally heavy rainfall is the main concern, but a wind gust to 45 mph can't be ruled out in the a stronger storm.

- Next chances for rain and storms return Monday night into Tuesday night. Isolated severe storms and pockets of heavy rain are possible.

UPDATE

Issued at 343 AM CDT Sat Aug 15 2026

No significant changes to the forecast this morning.

Low stratus and patchy, locally dense fog continues over the area this morning. A few sites have dropped around and below half a mile; will continue to monitor for potential headlines. Fog lifts through the morning, with stratus continuing into the afternoon ahead of a front. Still some questions as to how quickly the stratus lingers, and therefore how much we'll warm up and the amount of instability around. That said, scattered showers and storms remain in the forecast today into tonight as a mid level wave and the aforementioned front move through.

Locally heavy rain still is the main threat with any thunderstorms, with tall and skinny CAPE profiles, PWATs around 1.5-2", and a deep warm layer. Main concern for flash flooding would be near and south of US Hwy 20, where locally heavy rain has fallen the last few days. The NAM remains the most aggressive with instability later today (over 2000 J/kg), with most models lower. With MUCAPE around 1500 J/kg, 0-6 km shear less at or less than 30 knots, and meager low level lapse rates, severe weather is unlikely. But can't rule out some isolated gusts around 45 mph if lower levels dry out, and a few of the hi-res models show this potential. Storms continue to push east through the evening and into the early overnight.

Still uncertainty with fog development late tonight into early Sunday morning with some drier air and slightly stronger winds. Patchy fog is possible, mainly in low lying areas. Sunday will be a dry and pleasant day with some sunshine.

DISCUSSION

Issued at 1236 PM CDT Fri Aug 14 2026

Low pressure continues to track east northeast into western IA through this afternoon. Scattered showers and isolated thunderstorms will be possible with this feature. The main effects should be this afternoon and confined to areas near and south of highway 20 in northwest IA. With PWAT values around 1.75" to 2", locally heavy rain will be possible, especially near this low pressure along and south of highway 20. Some question marks surround the air mass in Woodbury and Ida counties, locations that have received the most rainfall the past two days, as the morning stratiform rainfall seems to be providing some stability to the area and suppressing stronger convective activity. The latest Hi-res models continue to trend away from heavier rain near highway 20, with mainly spotty activity expected. A few downpours could lead to very localized amounts around an inch or so, but flash flooding is unlikely. Farther northwest, spotty showers will be possible with weak, diurnally driven instability. The overall effects of these diurnally driven showers will be low.

Saturday will likely start with stratus and fog in many locations. A weak wave will move through the area and likely lead to spotty showers and thunderstorms. Some hints that the better instability (about 1000 J/kg) will be north of I-90, but overall weak shear and 13 kft freezing levels suggest that pockets of heavy rain will be the main threat.

By Saturday night this wave will move southeast of the area, leaving mainly dry conditions in place for much of Saturday night into Sunday morning. Model soundings hint at the potential for some morning fog, but the depth of the low level moist layer looks much shallower, so a better chance to burn off in the morning. Drier northerly flow should lead to a pleasant Sunday with highs of 75 to 80 and dew points likely in the lower to mid 60s for most locations.

Sunday night into Monday should see mostly dry and warm conditions continue. Monday night into Tuesday night will be the next better chance for showers and storms as a trough digs in to the north and northeast. For now, the threat for severe storms and heavy rain looks low, but this will be a time frame to watch for changes.

Cooler and more stable air should settle in behind this system, with highs mostly in the 70s Thursday and Friday and only isolated chances for showers and storms.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1256 AM CDT Sat Aug 15 2026

Areas of fog and stratus continue to impact the forecast area early this morning. Any fog should lift by 14-15z. Confidence remains low in the extent of any dense fog, but it's certainly possible in spots (20-60% chance). Stratus will gradually lift through the daytime morning hours, eroding or lifting to VFR levels by the early to mid afternoon.

Scattered showers look to develop through the day on Saturday, with better chances for thunderstorms embedded within this activity occurring for areas in the quadrant near and east of I-29 and near and south of I-90. Winds will be light and variable through the mid morning hours, picking up to around 5-10 kts throughout the day out of the west-northwest. A cool front moves across the area through the afternoon, turning winds more of a north-northwesterly direction to end the period.

FSD WATCHES/WARNINGS/ADVISORIES

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