Area Forecast Discussion

KEY MESSAGES

- Dense fog continues early this morning in east-central South Dakota and adjacent areas of southwest Minnesota. Fog should dissipate by 4-5 am as drier air moves in.

- A few additional thunderstorms may develop into early this morning along Highway 20, capable of mainly small hail. There is a very low (5% or less) chance of a quarter sized hailstone in the strongest storms.

- 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.

UPDATE

Issued at 908 PM CDT Mon Sep 14 2026

A cold front continues to move across the area into tonight. Ahead of the front, some area cameras have shown drizzle in some of the lower stratus that has developed in mainly eastern South Dakota north of I-90. This is supported by soundings showing this near surface stratus layer with a depth of around 1.5 km. May see some of this drizzle move into southwest Minnesota, with the threat from this being temporarily reduced visibilities on the roads as this stratus drifts east-southeastward this evening.

A line of light showers from roughly Storm Lake to Smithland, IA has not been able to develop into much of anything despite some elevated instability. Only really the 14.18Z NAMNest blows things up to anything noteworthy, but it appears to be overestimating instability values by about 1,500-2,000 J/kg. Nonetheless, sufficient instability (around 1,000-1,500 J/kg) remains along with ample effective shear values of 40-50+ kts and so if a stronger updraft can get going in our far southeastern areas tonight, large hail would be the primary concern. One limiting factor for severe hailstones making it to the surface will be freezing levels, which according to soundings is sitting around 15,000 ft. So we would probably need a longer sustained updraft and a storm to start rotating before quarters at the surface become a possibility. Not out of the question given the shear, but it is looking unlikely and thus the largest hail stones should storms develop would be dime to nickle sized. Any threat for hail looks to diminish towards sunrise tomorrow morning.

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 /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1252 AM CDT Tue Sep 15 2026

Dense fog has developed over portions of east-central South Dakota and adjacent areas of southwest Minnesota. This fog should disperse as drier air moves in from the west and winds pick up by 9- 10z, though lighter fog may linger farther south through about 12- 13z. A few showers and storms will remain possible mainly south of I- 90 through the early morning hours today, but widespread issues are not expected.

Winds will be mainly out of the northwest through the day Tuesday, becoming light and variable to calm by the evening hours. Strongest winds this morning will be over the higher elevations of the Coteau des Prairies and south-central South Dakota, where a few gusts to 20- 25 kts will be possible through the late morning hours today.

FSD WATCHES / WARNINGS / ADVISORIES

SD...Dense Fog Advisory until 5 AM CDT early this morning for SDZ039-040-054>056. MN...Dense Fog Advisory until 5 AM CDT early this morning for MNZ071-097. IA...None. NE...None.