textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers linger into the late afternoon hours. An isolated non-severe thunderstorm may try to develop in central South Dakota along a weak cold front.

- Thunderstorms remain possible in northeast Nebraska and northwest Iowa late this afternoon and evening, though trends favor higher risks to the south.

- However a few strong to severe storms may be possible late tonight and into early Tuesday morning along Highway 20, capable of large hail.

- Near normal temperatures continues the rest of the week with low rain chances on Wednesday, but significantly higher chances on Friday. Friday's risk could bring a low severe weather risk by the evening.

DISCUSSION

Issued at 122 PM CDT Mon Sep 14 2026

THIS AFTERNOON: Showers and isolated thunderstorms continue early this afternoon with considerable cloud debris across the CWA. Latest short term guidance continues to struggle to clear out enough of the warm sector as the prevalence of a persistent 40 knot LLJ through the CWA may just be too strong to overcome. This may result in a much lower surface based storm threat in the far southern CWA. There may still be narrow window, but feel this may end up closer to I-80 than Highway 20. Further west, a surface cold front continues it's trek southeast. Clearing ahead of this front in south central SD might be just enough to spark a thunderstorm or two towards Chamberlain and Gregory late this afternoon. Any storm should weaken quickly as it moves east.

TONIGHT: While stronger surface based storms may just be south of the CWA, we'll need to watch for a lower probability elevated storm risk late in the evening and early in the overnight hours. A secondary wave moves into Nebraska after 04Z, with soundings showing at least the potential for a few stronger updrafts when lifted off the 850:800 mb layer early in the overnight. Given reasonable shear at that time, an isolated large hail threat could develop over the far southeastern portions of the CWA. The cold front will push through the remainder of the CWA overnight, with a cooler northwest wind developing.

TUESDAY: High pressure will be in control of the CWA on Tuesday, with variable cloud cover leading to near normal highs around 70 degrees.

WEDNESDAY: Mid-lvl flow turns slightly to the southwest on Wednesday, allowing modest return flow to push low-lvl moisture back northward. While lift itself looks weak, a few showers and isolated storms may develop through the day. Soundings also show a high probability for lower stratus which may limit the overall temperature climb in the afternoon.

THURSDAY-FRIDAY: A similar setup continues for Thursday with broad but weak warm advection persisting through the Tri-State area on Thursday. Occasional light showers may develop north of a stalled warm front over central and eastern Nebraska. With low-lvl temperatures climbing slightly, we may see a small uptick in high temperatures towards the mid-upr 70s. The fly in the ointment here is the persistent southeasterly surface wind and cloud cover, which could lower the high temperatures towards the lower to middle 70s instead.

By late Thursday night and Friday, a stronger wave ejects out of the Central Rockies inducing stronger return flow and a sharpening of moisture advection back into the Dakotas. The nocturnal LLJ should induce scattered to numerous non-severe showers and thunderstorms into Friday morning. With surface low pressure forming over the western Dakotas during the day, a warm front may surge northward across the CWA by mid-day allowing temperatures to quickly climb into the 80s. This increased instability combined with a cold front that begins to move southeast late in the afternoon and evening could spark a few strong to severe storms into Friday evening. Though the quality of the warm sector, duration of morning stratus, always make severe weather risks this time of year more difficult to pinpoint this far out.

SATURDAY-SUNDAY: A stronger trough dips into the Dakotas for the weekend which favors lowering temperatures and more isolated to scattered shower development at times. The severe weather risks will remain low next weekend.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1242 PM CDT Mon Sep 14 2026

IFR to MVFR ceilings continue early this afternoon, with expected slow improvement through the afternoon and early evening. Scattered showers and isolated storms may persist into mid-afternoon, shifting slowly eastward.

A cold front approaches the western CWA later this afternoon and may have a narrow corridor of stratus with it. The longevity of this stratus remains in question, but feel it may sink into NW Iowa far SE South Dakota by 00Z.

Additional convection may develop late this evening but perhaps overnight south of I-90 and towards Highway 20 after dark. Considerable uncertainty remains, so will indicate with a Prob30 at this time. The front passes through Highway 20 after dark, and as typical this time of year, could lead to lingering stratus into Tuesday morning. Confidence too low to indicate prevailing MVFR ceilings, but will hint at potential with sct025 ceilings.

FSD WATCHES/WARNINGS/ADVISORIES

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