textproduct: Sioux Falls

KEY MESSAGES

- Fog is expected to develop later tonight and into early Wednesday morning. Moderate to high (50-70%) chances of visibility below a mile, mainly for south central South Dakota and areas north of Interstate 90.

- Rain and isolated storm chances return Wednesday into Wednesday evening. If storms can develop, an isolated stronger storm capable of half dollar sized hail and 60 mph wind gusts is possible between 3 PM and 8 PM CDT.

- Additional rain chances, including a few isolated thunderstorms, return late this week into the weekend.

UPDATE

Issued at 839 PM CDT Tue Oct 27 2026

Stratus remains in place tonight into much of Wednesday. Although we've seen some clearing across eastern SD into northwestern IA and southwestern MN, beginning to see some of this fill back in. Biggest question with fog development will be the coverage of stratus and how long winds stay a touch more elevated, which would keep fog development at bay. That said, ensemble probability of visibility less than a mile toward Wednesday morning is 50-70% (or higher), greatest along/north of I-90 and also across south central SD. Temperatures are already falling quickly into the 40s for areas that have seen some clearing. May need to make some adjustments to lows for these locations if we remain clear a bit longer into the evening.

Fog should clear mid to late Wednesday morning. Cold front moves through during the day, and there could be some morning showers with a push of WAA. Main focus will be the scattered showers and isolated thunderstorms that are expected to develop between the James River Valley and I-29 ahead of the cold front and mid/upper wave during the afternoon and evening hours. Latest hi-res guidance is shifting the initial development a bit further west and a little earlier, more toward James River Valley early afternoon. Still looks as though we'll have 500-1000 J/kg of MUCAPE, which could lead to some isolated thunderstorms. Main question when it comes to severe weather potential is that the better shear and lapse rates appear to be offset from the greatest instability during the afternoon. Parameters do line up a bit better toward the evening but by that point, instability will be waning due to the loss of peak heating. Severe risk may begin as early as 3 PM and linger into the evening (8 PM or so) with storms capable of half dollar hail and 60 mph wind gusts. Keep an eye on the forecast if you have outdoor plans.

DISCUSSION

Issued at 314 PM CDT Tue Oct 27 2026

Clouds will continue to gradually become broken from west to east for the remainder of this afternoon and into the evening. Those in central South Dakota may get a few glimpses of sunshine yet. Tonight winds will be light out of the south, and lows will be in the 40s to low 50s. Nearly calm conditions may result in dense fog development overnight. Ensemble guidance indicates a broad area of 50-70% probability of visibility of 2 miles or less. While the worst conditions look to remain along and north of I-90, caution should be used everywhere. Fog may linger into the mid-to-late morning.

Looking aloft for Wednesday we see a broad wave taking shape over western Canada, extending down over the central High Plains. At the surface a low pressure will settle over central Canada and a cold front will develop and drape from there through eastern North Dakota, central South Dakota, and into southeastern Wyoming. Moderate warm air and moisture advection will pool ahead of this front, working to destabilize the boundary layer. Highs will climb into the 60s to the low 70s over northwest Iowa, while dewpoints climb into the upper 50s and low 60s. Though skies will be partly cloudy, surface heating through breaks in the clouds may work to further destabilize the environment, especially east of I-29. MLCAPE of 500-1000 J/kg is possible. Mid-level lapse rates will be marginal at 6.5 to 7.0 deg C. However, the 0-6 km bulk shear will be 40+ kts, enough to support a stronger thunderstorm or two. As the upper level trough, upper right jet entrance region, and surface front move to the east scattered showers and thunderstorms are expected to form over central South Dakota in the late morning to early afternoon. As this system continues to pivot, storms will expand to the east mostly along and north of I-90. By mid-to-late afternoon the axis of the upper trough and surface front will cross into the area of best thermodynamic parameters east of I-29. A few stronger, possibly severe thunderstorms may develop. While conditions are favorable of surface based supercells, strong boundary layer capping will likely keep most storms elevated and sub-severe producing small hail and wind gusts to 45 mph. Should a stronger surface based storm develop, it could produce large hail up to the size of a half dollar, and damaging wind gusts in excess of 60 mph. This matches well with the latest SPC Day 2 outlook with a Marginal (level 1 of 5) Risk of severe storms. Despite the chance for stronger storms, most will only see a few hundredth to a couple tenths of accumulation. Those under any stronger storms could see up to an inch. Storms should push east of the CWA by midnight Thursday morning. Cold air advection behind the front on northerly winds will reduce overnight lows to the mid 30s to 40s.

Thursday will be dry but cooler as flow aloft becomes quasi-zonal and surface high pressure pushes in from the northwest. As the high moves into central Minnesota through the afternoon winds gradually change from northerly to east-southeasterly. Soundings indicate mixing will be shallow in the afternoon, only reaching up to around the 925 mb layer. Temperatures in the 925 mb layer have been trending slightly down over the past few model runs. In addition, lingering clouds may also limit surface heating. After collaboration with neighbors have opted to reduce NBM high temperatures a couple of degrees by blending it with CONSShort. Highs are now expected to climb into the 50s to mid 60s.

Friday will be mostly dry as we watch the approach of a strong upper wave from the southwest. Highs will climb into the upper 50s and mid 60s. Friday late afternoon into the evening the wave and surface low will begin producing showers and thunderstorms that will slowly move north to northeast through Friday night and most of Saturday. Saturday evening and most of Sunday will be dry with highs in the 50s and 60s. Followed by another strong upper wave that will bring extended chances for rain into the first half of next week. Long range ensembles indicate a high probability (70-90%) of total rain equal to 1 inch or more from Friday evening through next Wednesday. Further details are vague at this point and there is much uncertainty with track and evolution of these waves.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1040 PM CDT Tue Oct 27 2026

MVFR and IFR stratus has expanded to the northwest, stretching from northern NE to KAGZ to K6E5 into northeastern SD. Some LIFR ceilings have developed in northwestern IA. Further west in central SD, beginning to see fog develop with some MVFR and IFR visibility. Still expecting stratus and fog to linger overnight, with some uncertainty on coverage of fog v.s. stratus. MVFR to IFR conditions prevail, with some visibility below 1 SM at times.

Isolated showers are possible through the I-29 corridor Wednesday morning, but have left mention out of KFSD for now. Additional scattered showers and isolated thunderstorms expected in the afternoon and evening hours, mainly east of the James River. Confidence is low on TS coverage, so no mention for now.

Lighter southerly winds overnight into Wednesday increase and shift northwesterly behind a cold front. Gusts around 20 knots expected Wednesday afternoon and evening. Light northwesterly winds Wednesday night may allow for some valley fog.

FSD WATCHES/WARNINGS/ADVISORIES

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