textproduct: Sioux Falls

KEY MESSAGES

- Isolated thunderstorms may form across south central South Dakota and north central Nebraska after midnight, bringing low risks for hail. Widespread severe weather is not anticipated.

- Patchy fog is possible Saturday morning along low areas and water ways.

- Considerable uncertainty remains in the forecast for much of the upcoming 5 days, with relatively low, but not zero, risks for rain each day.

- Severe weather risks also remain uncertain, with some focus for stronger storms Saturday night, late Sunday into Sunday night, and again Monday night into Tuesday

- Temperatures remain near seasonal normals into mid-week, with potential cooler weather late next week.

UPDATE

Issued at 911 PM CDT Fri Aug 7 2026

No remarkable changes to the forecast this cycle. Winds overnight become light and variable. This may allow for patchy fog to develop for areas east of Highway 81. Fog should remain mostly confined to low areas, ponds, and water ways. Any fog that does form should burn off by mid-Saturday morning. After sunrise winds will become southerly as a surface high drifts to the southeast of the region. A subtle mid-level wave will result in an increasing LLJ over western South Dakota overnight. As the wave progress to the east winds will begin to increase early Saturday morning. Gusts of 20-30 mph are expected for areas along and west of I-29 by Saturday afternoon. Gusts to the east will generally be 20 mph or less. Highs for Saturday are expected to climb into the 80s.

A low pressure system associated with the wave located along the western ND/SD border will drag a warm front through the region. WAA ahead of the front coupled with the LLJ and weak elevated instability may be enough to trigger showers and thunderstorms over south central South Dakota Saturday morning. Guidance is in very low agreement on how storms will evolve and their coverage. Most CAMs keep storms along the Missouri River and moving southeast through the day. The more coarse GFS, EC, CAN, and NAM bring storms through the CWA during the day as the low passes to the north and drags the warm front through. In either case, the region is strongly capped which will likely work to limit severe weather risks. However, while confidence is low in widespread severe weather, there is a non-zero chance an isolated storm or two could become strong to severe. Risks with stronger storms include wind gusts to 60 mph and hail the size of a quarter.

DISCUSSION

Issued at 105 PM CDT Fri Aug 7 2026

THIS AFTERNOON: Convection earlier this morning continues to move east and away from the area early this afternoon. A cool front also continues to push southeast, already well into NW Iowa. Behind this boundary, periods of very low stratus with drizzle have been reported. As stronger dry air advection moves southeast, we should continue to see stratus erode. Temperatures with all the cloud cover have been stuck in the upper 60s to lower 70s, with a small areas ahead of the front in the lower 80s. As long as clouds clear by mid-afternoon, there should be enough time for highs to still reach the upper 70s to lower 80s.

TONIGHT: High level wildfire smoke will continue to leave a milky sky overhead. However we've seen little impact on overnight lows with this smoke, so with the continued dry air advection southward this afternoon and evening, we are likely to see low temperatures in the lower 50s by Saturday morning. One area to watch after midnight will be in central Nebraska into central South Dakota, as guidance continues to hint as a subtle wave entering the Dakotas. This wave should induce a stronger LLJ which in return may produce enough focused convergence for a few stronger thunderstorms. The general track of any strong activity should be south southeast along the elevated instability axis into east central Nebraska. Nevertheless, if a storm could develop near Gregory County, 1.5" hail would be the main risk.

SATURDAY: Forecast confidence remains lower for Saturday regarding precipitation chances. Guidance is quite split on where the axis of stronger low-lvl jet convergence will drift through the day. Most of this uncertainty is due to poor model resolution of any weak vorticity passing through the 700:500 layer. Some models keep the best lift bottled up south of the Missouri River with an MCS moving towards western Iowa. Others have a wave further north, pushing the LLJ towards I-29 by mid-day and leaving a few lingering showers and clouds overhead into the afternoon. What fairly certain is that MUCAPE will struggle to lift northeast, keeping any very isolated severe weather risk focused along or south of the MO river into mid- day. By the late afternoon and evening, the instability pool does drift northward, however soundings also show a fairly stout capping layer overhead that should inhibit convection given weak and transient lift. One note: If we do end up with at least a thick mid- lvl cloud field over the heart of the CWA by mid-day, then high temperatures could be significantly impacted and convection risks lower even further. Rain chances may continue Saturday night, though focus moreso over Iowa and western Minnesota as the LLJ redevelops and interactions with a developing elevated frontal boundary. Confidence is very low with these precipitation risks.

SUNDAY: Any nocturnal convection Saturday night could play a role in redevelopment on Sunday. Again though, the myriad of potential small shortwaves moving through the NW flow is problematic with model guidance which shows a wide range of solutions. Some guidance shows a mostly dry day and night with subsidence and high pressure moving through. Others maintain a surface and elevated frontal boundary in the area, with increasing lift late in the day and some isolated strong to severe storms. Given the spread in models, low probabilities spread through the evening and early overnight models continues to be the best way to suggest the potential at this stage.

MONDAY-THURSDAY: There will really be no change in the forecast into the middle of the week as the region remains under slight northwesterly flow aloft. This flow will keep a persistent risk for daily convection, though with extremely low confidence and predictability until a day or so before. There continues to be some focus for lift around the Monday night/Tuesday and again Wednesday night and Thursday timeframe where an MCS could form. Temperatures may fall back slightly into the lower to middle 80s near the seasonal normals, with potential for a larger cooldown by next weekend.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1220 AM CDT Sat Aug 8 2026

VFR conditions are expected for the period. Light and variable winds overnight may allow for patchy fog formation in low areas and along water ways, especially for areas to the east of Highway 81. Fog is expected to burn off around mid-morning. As the sun begins to rise winds will become southerly and increase through the morning. Afternoon gusts of 15-25 kts are expected for areas along and west of I-29. Areas to the east will generally experience gusts of 15 kts or less. Winds remain slightly breezy through the end of the period.

There are chances for showers and thunderstorms early Saturday morning over south central South Dakota. An isolated storm or two may become strong to severe. Threats include wind gusts to 52 kts and hail to the size of a quarter. Storms track along and south of the Missouri River through mid-day. A second round of showers and thunderstorms are possible in the afternoon along and north of Highway 14. As storms progress east a few may sink south but look to remain north of I-90. As storms move into southern Minnesota some may become strong to severe in the evening to overnight with marginally severe winds and hail the main threats.

FSD WATCHES/WARNINGS/ADVISORIES

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