textproduct: Sioux Falls

KEY MESSAGES

- Low chances (less than 20%) for showers and storms through sunrise south of the Missouri River. Severe weather risk is not expected.

- Slightly cooler weather for the weekend. Saturday should remain dry with rain chances (40-70%) returning to portions of the area by Sunday morning. Rainfall amounts could exceed a tenth of an inch.

- Additional chances for rain, and potentially strong to severe thunderstorms (5-15%), are possible through next week. Details are uncertain, so continue to check the latest forecast for the most up to date information.

UPDATE

Issued at 831 PM CDT Fri Aug 21 2026

No major changes to the forecast for tonight and tomorrow. A weak boundary heading towards I-90 has set off a few showers and storms as it moves southward, mainly over southwest Minnesota and far eastern South Dakota. Should see this continue weakening with southeastward extent as we lose daytime heating. Meager instability is in place, so just expecting weak thunderstorms with brief downpours and some lightning over roughly the next hour.

Higher instability values (2,000+ J/kg of MUCAPE) are located near and south of the Missouri River, but this will slowly sag southward through tonight, though some guidance keeps around 1,000- 1,500 J/kg in place over Gregory County through the early morning hours. With the better lift to the south of the area, thunderstorms are unlikely. If a storm were clip our area, severe weather is unlikely as skinny CAPE profiles would really hinder the development of any large hailstones and the elevated nature of any storm would preclude a damaging wind threat. Any storms will be well south of the area by sunrise Saturday, leading to a warm and pleasant late summer day!

DISCUSSION

Issued at 139 PM CDT Fri Aug 21 2026

Quiet conditions persist this afternoon as temperatures have warmed to the 70s and 80s across the area. Quiet conditions are expected to continue for the rest of the day as the cold front has fully pushed through the area. This will keep storm chances south and west of the forecast area. Can't rule out the low possibility (less than 20%) of a shower or weak storm passing along and south of the Missouri River this afternoon, evening, and potentially into the overnight hours. Should this occur, the chance for a severe storm is low. Surface ridging will begin to slide into the forecast area tonight, resulting in light and variable winds with lows falling to the upper 50s to low 60s. Patchy fog is again on the table but with drier air in place, think that any fog that does develop will once again be tied to a few river valley's.

Saturday begins the weekend on the quiet side as high pressure pushes through the Northern Plains. High temperatures will be a bit cooler in the upper 70s to low to mid 80s, with a continuation of light northerly winds. This will make for a wonderful Saturday, perfect for outdoor activities! Rain chances will increase late Saturday night through Sunday as a weak shortwave trough rounds the top of a building upper level ridge. This will result in increasing chances for rain across the area for the day on Sunday. Cloud cover with the associated chances for rain will keep high temperatures a bit cooler in the upper 70s to low 80s. While some showers are possible during the morning timeframe, the highest chances for rain will come Sunday evening and night as the main shortwave pushes through the area. The ensembles show a broad 40-70% chance for rainfall totals to exceed a tenth of an inch. Soundings show some elevated instability in place so thunderstorms are possible, though severe storms are not expected at this time due to weak shear profiles. With non-severe storms on the table, rainfall amounts could be locally higher depending on how storms track.

An active pattern continues aloft for next week. Medium range guidance shows shortwave troughs continuing to push through the Northern Plains within the northwest flow regime. This will lead to chances for rain almost every day next week. However, the ensembles show a large variance in rainfall probabilities due to the differences in these upper level features. Latest machine learning (ML) guidance does show low probabilities (5-15%) for severe weather throughout the week. Details for severe weather remains uncertain so continue to check the forecast for the most up to date information. Aside from rain and storm chances, high temperatures look to remain in the upper 70s and 80s.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1229 AM CDT Sat Aug 22 2026

Patchy light fog is possible tonight mainly in river valleys and other low lying areas, though widespread issues are not expected. The only TAF site that appears to at least have a chance of light fog is KHON, but even then we're looking at a less than 15% chance of development there.

Quiet conditions are expected through the period outside of a rogue thunderstorm south of the Missouri River through sunrise today. Light and variable winds are expected through daybreak. Then winds will be mainly out of the north-northeast around 5-10 kts through the day today, but will start turning more easterly into the later evening hours.

FSD WATCHES/WARNINGS/ADVISORIES

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