textproduct: Sioux Falls

KEY MESSAGES

- The next better chance for showers and storms is Sunday night (50-70%). Locally heavy rain and isolated severe storms are possible.

- Otherwise most days through next week will see highs in the 80s and lows in the upper 50s to lower 60s.

UPDATE

Issued at 845 PM CDT Sat Aug 22 2026

No major changes to the forecast tonight and tomorrow. Mid to high level clouds are moving into south-central South Dakota associated with our next weak wave moving in. These clouds will continue pushing east-southeastward through the night, and the aforementioned wave will help set off some showers and weak thunderstorms starting in south-central South Dakota early tomorrow morning with this activity gradually spread east- southeastward through the day on Sunday. As it moves eastward, it will outrun any appreciable instability and become just hit or miss light showers/sprinkles as it approaches I-29.

Heavy rain looks to be the main threat heading into Sunday night as the low level jet kicks up and sets off more elevated thunderstorms with the aid of an upper wave moving in from the northwest. With the potential of multiple updrafts going up around the same time, there will be plenty of competition for the strongest updraft and this will help limit a severe weather risk. However, if one or two storms can go more isolated and become a more dominant updraft, then perhaps some large hail will be possible given effective shear values around 40-45 kts. Freezing levels will be quite high though, so even if an updraft can sustain itself, hailstones will have a pretty deep warm layer to go through before it were to reach the surface.

DISCUSSION

Issued at 142 PM CDT Sat Aug 22 2026

A quiet night is ahead as high pressure drifts east. Southerly flow will develop in central SD later tonight and become more established across the area through Sunday. The light winds will allow temperatures to fall into the lower 50s, especially east of I- 29.

The upper level wave responsible for the low level winds turning southerly will move into central SD tomorrow morning, and eastward and southeast from there through the day. With fairly stout low to mid level dry air, mainly an increase in cloud cover is expected through the morning. The exception will be south central SD where enough moisture may allow for 500-1000 J/kg of elevated CAPE, which will support some spotty showers and thunderstorms. Severe weather is not expected.

Lift will gradually increase through the day into Sunday night, when a moderately stronger LLJ focuses on the area. Given fairly weak shear and CAPE values generally under 1000 J/kg, severe weather looks unlikely. However with a freezing level around 13 kft, locally heavy rain will be possible. Not much agreement on the location of the heavier rain with the models pretty inconsistently placing the mid level wave across the area. Some hints that the LLJ will focus somewhere on the SD side, but confidence is low.

This wave moves out of the area on Monday but another weaker wave moves by to the north on Monday night and brings a small increase in warm air advection, which could spark a few showers and thunderstorms.

Mainly northwest flow aloft continues Tuesday into next weekend. This will bring periodic small chances for showers and thunderstorms throughout the week with little agreement on exactly when. Otherwise lows should mainly be from the mid 50s to mid 60s with highs in the 80s.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 626 PM CDT Sat Aug 22 2026

very patchy fog is possible late tonight into Sunday morning, mainly in river valleys and other low-lying areas. Scattered showers and isolated thunderstorms will move into south-central South Dakota late tonight and drift southeastward through the day on Sunday.

Winds will turn light and variable near and east of I-29 heading into tonight. Meanwhile, areas west of I-29 will see winds pick up a bit out of the east and then southeast heading towards daybreak Sunday. Winds will pick up across most of the area through the day Sunday out of the south. Winds will get pretty breezy west of the James River Sunday afternoon, where gusts of 25-30 kts are expected.

FSD WATCHES/WARNINGS/ADVISORIES

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