textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and a few storms are likely early this morning in south-central South Dakota, with some lingering activity possible into the afternoon. Severe weather is not expected, but locally heavy rainfall will be possible during any afternoon storm.

- The next better chance for showers and storms across a wider part of the area is tonight (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 /06Z TAFS THROUGH 06Z MONDAY/

Issued at 1226 AM CDT Sun Aug 23 2026

Patchy fog remains possible mainly in low lying areas and river valleys east of I-29 early this morning, though widespread issues are not expected. Scattered showers and a few thunderstorms look to move into south-central South Dakota towards daybreak, with any activity weakening as it moves east-southeast through the day.

A better chance of storms arrive late this evening into the Sunday night hours, mainly near and south of I-90, though this won't make it near the TAF sites until either the very end or just after this period. With that timing uncertainty, left out mention of -TSRA at KFSD and KSUX. A second area of storms to watch will be anything that could drop southward from northern South Dakota and move towards KHON. Did add a PROB30 group there for this potential since there was higher confidence this would occur more towards the end of the period as opposed to afterwards.

Winds will pick up as we head into the daytime hours Sunday, turning more southeasterly and then southerly with time. Strongest winds will be in south-central South Dakota where winds may occasionally gust to 25-30 kts this afternoon. Winds will slacken somewhat this evening outside of any thunderstorms, though it will still remain breezy to close the period in south-central South Dakota where winds could gust up to 20-25 kts to end the period.

FSD WATCHES/WARNINGS/ADVISORIES

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