textproduct: Sioux Falls

KEY MESSAGES

- Isolated, non-severe thunderstorms continue across northwestern Iowa through daybreak. Severe weather is not expected, but locally heavy rain has been occurring and may lead to isolated flash flooding.

- Isolated to scattered showers and storms are possible along and north of I-90 this morning into early afternoon. Severe risk is low.

- Additional scattered and possibly severe storms expected late this afternoon across southeastern and south central South Dakota, moving east through tonight. Ping pong ball sized hail, 60 mph wind gusts, and brief heavy rain are the main threats. A tornado or two possible.

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

UPDATE

Issued at 339 AM CDT Mon Sep 7 2026

An area of showers and storms continues over northwestern IA into southeastern SD early this morning, tied to a wave and some LL convergence. Although severe weather is not expected, am concerned with flash flooding due to training storms over northeastern Woodbury and into northwestern Plymouth county - have seen reports of over 3 inches since midnight and issued a Flash Flood Warning through 6 AM for this area. May see further development in this area into southwestern MN through the morning hours as the 700 mb wave lifts north.

Further west, watching the activity across western SD/NE which is tied to the next wave and another segment of the LLJ. This may be the catalyst for additional showers/storms, mainly north of I-90, mid-late morning into the early afternoon hours. Severe weather risk is low with these storms.

Main focus is with the increasing LLJ later this afternoon and tonight, in tandem with main trough ejection from the Rockies. Leading wave and LLJ along with a surface boundary and destabilizing atmosphere should provide the catalyst for showers and storms to develop. Instability All modes of severe weather are possible from roughly 5 PM through 1 AM, as initial discrete cells may grow upscale and move east. Shear at all levels increases through the evening, and increasing mid level lapse rates will also be supporting of hail to the size of ping pong balls - possibly larger if a storm can maintain discrete status for longer. A tornado or two are possible with surface based storms with curved hodographs and increasing shear in the lowest levels. 65 mph wind gusts are also possible. May see some locally heavy rainfall as well, but more progressive storm motion should help limit widespread concerns. Localized flash flooding is possible, especially if storms move over areas which have seen recent heavy rain.

Still questions for Tuesday regarding where the surface boundary ends up and impacts from overnight/early morning convection. Better shear looks to be offset from the greatest instability which lies ahead of the front. Could see a stronger storm or two across northwestern IA and adjacent areas of central MN/eastern NE/far southeastern SD in the afternoon and evening.

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 /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1238 AM CDT Mon Sep 7 2026

Scattered light showers are ongoing over northwest Iowa. These will taper off over the next few hours. VFR conditions for the overnight except for areas in southwest Minnesota where winds have become light enough for patchy fog to form. Fog will dissipate as southeast winds increase through 07.12Z. Gusts west of I-29 will be 20-27 kts, while gusts to the east will be 20 kts or less. Breezy winds expand east through the afternoon with gusts of 20-30 kts with a few gusts to 33 kts possible over south central South Dakota. Winds remain gusty through the end of the period.

We'll be watching for two rounds of showers and thunderstorms tomorrow. The first round looks to begin around 07.15Z through the late morning to early afternoon. This round looks to remain mostly north of I-90. Widespread severe weather is not expected, however an isolated storm may become strong to severe producing 1 inch hail and 52 kt winds. The second round looks to begin in the late afternoon to early evening. This round brings increased potential for severe weather. Initial storm mode over central South Dakota will most likely be supercells. These could produce hail up to the size of a ping-pong ball, heavy rain, and wind gusts to 60 mph. Though the risk is low an isolated tornado is also possible. As storms approach the I-29 corridor they may begin to grow upscale into a broken line to a QLCS. Hail threats diminish to marginally severe but wind risks increase. Isolated brief spin ups and weak tornadoes are also possible along bowing sections. Storms will be ongoing east of I-29 through the end of the period.

FSD WATCHES/WARNINGS/ADVISORIES

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