textproduct: Sioux Falls

KEY MESSAGES

- An unsettled pattern persists through Labor Day. The highest overall rain chances remain south of I-90, however scattered afternoon/evening showers and storms will occur farther to the north.

- Widespread heavy rain is not expected, but ribbons of heavier rainfall exceeding an inch are possible where narrow bands of showers/storms persist for multiple hours.

- Severe weather risk is low, but we continue to see a non-zero risk for weak funnel clouds with developing air mass showers during the afternoon-early evening.

- Chance of showers/storms lingers into Tuesday-Tuesday night. The severe weather risk remains low.

- An unseasonably strong upper level low will bring a shot of colder air to parts of the Northern Plains/Upper Midwest mid to late week.

DISCUSSION

Issued at 415 AM CDT Sun Aug 31 2025

SUNDAY-LABOR DAY: A slow moving mid-upper level low over eastern Nebraska will continue to drift southeast over the next 24-48 hours. This feature will keep a moderate to high (50-80%) chance of showers and a few thunderstorms across our southern forecast area into Monday, though chances will gradually wane from north to south Monday into Monday night as the low slides farther away from our area.

Areas roughly north of I-90, perhaps more along a line from Huron-Sioux Falls-Spencer Iowa, the nighttime-morning hours will tend to be on the drier side. However, similar to Saturday, diurnal heating will support bands of showers and scattered storms rotating west-northwest around the upper low to our south. This will result in highly variable rainfall across the area, but as we saw yesterday, if these showers/storms track along the same trajectory with little north-south variation in the band location, narrow ribbons of heavier rainfall will again be possible. Very difficult to project exactly where these narrow ribbons will occur, though, and as such the QPF forecast is low confidence.

By Monday afternoon/evening, as the low is farther southeast, we should begin to see some influence of drier air with a lesser chance of locally heavy rainfall.

High temperatures for the latter half of the holiday weekend should again be highly dependent on rain coverage. Cooler temps holding in the mid-upper 60s are more likely in our southwest and south where rain could be more prevalent, while northeast areas where we could see some sunshine should reach at least lower-mid 70s.

TUESDAY-EARLY WEDNESDAY: A much stronger northern stream trough will drop south into the northern Plains-Upper Midwest Tuesday night into Wednesday. While the main cold front will accompany the trough during this period, a pre-frontal trough and leading weak wave will keep a chance for scattered showers/storms over the area Tuesday-Tuesday night. Although deep layer shear does increase slightly with 30+kt possible Tuesday afternoon-evening, mid-level lapse rates remain unimpressive and DCAPE is also weak within the area of expected showers. Thus the severe weather risk continues to look low for this period.

LATER WEDNESDAY-SATURDAY: Latest deterministic models keep the brunt of the cold air with a strong secondary cold front over Minnesota, grazing just the northeast portion of our forecast area Wednesday night-early Thursday before slightly warmer air builds back in from the west. That said, the latter half of the week continues to look below normal for temperatures, but some uncertainty in just how far below our early September normal highs around 80F. Given the proximity of the stout upper low, cannot rule out spotty diurnal shower activity, but confidence in location is low, so will stick with a dry late week forecast for now.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 644 AM CDT Sun Aug 31 2025

We start the day with areas of dense fog in southwest Minnesota with scattered light showers and areas of MVFR to IFR ceilings across the western and southern portions of the forecast area.

Similar to Saturday, expect fog and ceilings to lift to VFR levels in most areas by midday, with a broader coverage of scattered showers and thunderstorms during the afternoon to evening hours. While there is some uncertainty whether TAF sites will be directly impacted by the late day storms, did include a mention at both KHON/KFSD for a few hours.

Potential for thunder wanes after 01Z-02Z, but spotty showers may linger, with lower stratus and fog again possible by the end of this TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...Dense Fog Advisory until 10 AM CDT this morning for MNZ071-072- 080-081-089-090. IA...None. NE...None.