textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and thunderstorms will continue for areas south of I-90 through the evening. Showers should remain below severe criteria.

- Isolated to scattered morning showers are possible along and north of I-90. These are not expected to be severe.

- Isolated strong to severe storms will again be possible late Monday afternoon into Tuesday morning. Large hail up to the size of a ping-pong ball, wind gusts of 60 mph, heavy rain are all possible. Though the risk is low, an isolated tornado is also possible.

- Quiet but continued warm conditions are expected for the rest of the work week.

UPDATE

Issued at 934 PM CDT Sun Sep 6 2026

An area of convergence along a surface boundary will keep showers and thunderstorms in the forecast for much of the overnight. Storms will most likely remain along and south of I-90, but it is possible a few may sneak farther north, especially along and east of I-29. These storms are not expected to be severe, however they could still produce 40-50 mph wind gusts and brief periods of heavy rain.

Through the overnight southerly 850 mb winds advect in a plume of warm and moist air. By sunrise a marginally unstable environment will be in place with a low amplitude wave approaching out of the southwest and an increasing LLJ. This could trigger a morning round of elevated showers and thunderstorms if a parcel can lift off the 850-700 mb layer. Wide spread severe weather is not anticipated, however one or two storms may become strong to severe producing hail to the size of a quarter and wind gusts to 60 mph. These should stay along and north of I-90 as they progress to the east. Timing is most likely between 10 am and 3 pm Monday.

Meanwhile, Theta-e continues to advect in forming a deep ridge over central and eastern South Dakota north to the Canadian border. Instability continues to increase ahead of deepening trough over the eastern Rockies. This trough ejects out onto the Plains in the early afternoon and a surface low pressure forms. The LLJ increases in response to a tightening SPG. By mid-to-late afternoon the cap west of the James River will have mixed out, and the low and associated frontal boundary will be at our western CWA border. Models vary a bit but in general expect 1500-2500 J/kg MUCAPE, 35-45 kts of Bulk shear, marginal mid-level lapse rates, but steep 7+ C low level lapse rates to be in place by this time. As the boundary sweeps through the LLJ continues to increase to 50 kts. Initial convection has the potential to be strong to severe producing large hail the size of a half dollars up to ping-pong balls, heavy rainfall, and wind gusts to 60 mph. A sharp clock wise curve to the hodograph and enhanced stretching potential combined with surface to 1 km SRH of 195 m2/s2 and surface to 3 km SRH of 300+ m2/s2 all indicate the potential that upon convection initiation a storm or two could produce a tornado. This probability is low, but still needs to be mentioned. Timing of greatest severe risk looks to be between 6pm Monday and 1 am Tuesday. Storm mode looks to be initially super cellular with deep layer shear vectors nearly perpendicular to the front. Over time the vectors become orientated at a 45 degree angle, which would likely result in supercells growing into a broken line.

Certainty in the late afternoon/evening storms is low to medium, due to the fact that morning convection may work over some of the environment. Depending on when those storms and clouds clear out will impact how well the atmosphere recovers.

DISCUSSION

Issued at 1246 PM CDT Sun Sep 6 2026

THIS AFTERNOON: Strong convection continues to develop in areas along but mostly east of I-29 this afternoon. The area continues to reside in a moderately unstable environment, but lacks any meaningful shear and mid-lvl lapse rates. However, climatologically significant PWATs are in place, with enough DCAPE to suggest an increased risk for wet microbursts over the next 1-3 hours in a narrow corridor from Madison to Sioux Falls, Sioux Center, Cherokee, Storm Lake, Le Mars, and Sioux City. Rainfall may be the most impactful hazard this afternoon with 1-2 hr totals of 3-4" already in portions of southern Minnesota. Additional convection is likely to continue to produce 2-4" totals in pockets of NW Iowa, though cold pool development may help push storms off an area before extreme values may be produced. The stronger MCV will also nudge it's way northward later this afternoon, and may work to produce additional northward/northeastward convection with it.

TONIGHT: This shortwave/MCV will drag it's feet eastward this evening, with some expected weakening of convection with the lost of daytime heating and general stabilization of the environment nearby. However, an increased LLJ may begin to develop after 02Z which could bring returning elevated showers and isolated thunderstorms to the CWA late this evening and continuing into the overnight hours. This activity will likely not be severe, but any shower could still bring brief heavy rain.

MONDAY-TUESDAY: Elevated shower activity diminishes towards daybreak as shortwave ridging arrives. An ejecting trough out of the Rockies will bring additional elevated convection into central and northern South Dakota into Monday afternoon, perhaps grazing the western CWA. As the EML gradually erodes into south central SD late in the afternoon, a few strong to severe storms may develop and track east southeast into the early overnight hours. As the LLJ increases after dark, elevated convection may expand in coverage with continued low- end severe weather risks for Tuesday morning.

More uncertainty for Tuesday, which is focused moreso on the location of the surface front and impacts of overnight elevated convection. While the primary surface front settles in northwest Iowa, a secondary stronger dew point gradient arrives later in the afternoon. Should sufficient clearing develop, then a storm or two could become stronger by mid-afternoon with activity quickly tracking southeast by the evening.

EXTENDED: With ongoing convection, no forecast changes made to the extended as a temporarily reprieve from active weather develops. Temperatures may still remain near to above normal for the rest of the work week.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 643 PM CDT Sun Sep 6 2026

Scattered showers and thunderstorms linger along and south of Highway 18. These will continue to move east and expand north, keeping chances for storms in the TAFs until around sunrise Monday. A brief lull before a weak wave moves northeast out of western Nebraska. Renewed chances for scattered thunderstorms from central South Dakota northeast into southwest Minnesota are expected for the remainder of the period. Widespread severe weather is not anticipated, however an isolated storm may become strong producing marginally severe hail and wind gusts. Storm chances continue beyond the end of this period.

Breezy southeast winds gusting 15-25 kts will continue through the overnight. Near sunrise winds will increase with the approach of the previously mentioned wave. Widespread afternoon gusts of 20-30 kts are expected. Highest gusts will be along and west of the I-29 corridor. Gusty winds continue through the end of the period.

FSD WATCHES/WARNINGS/ADVISORIES

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