textproduct: Sioux Falls

KEY MESSAGES

- Patchy fog, some locally dense, will continue to impact the area through the morning commute. Though widespread dense fog is not expected, be sure to use extra caution on the roads. Fog should lift by the mid to late morning.

- Rain and isolated storm chances return Wednesday into Wednesday evening mainly near and east of I-29. If storms can develop, an isolated stronger storm capable of ping pong ball sized hail and 60 mph wind gusts is possible between 1 PM and 8 PM CDT.

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

UPDATE

Issued at 313 AM CDT Wed Oct 28 2026

Low stratus continues to build northeastward early this morning, though we're also seeing some breaks in the clouds over portions of northwest Iowa. This has allowed for some fog to develop there, which has been locally dense at times. Other areas seeing locally dense fog include the higher elevations of the Coteau des Prairies where the stratus has lowered enough to reach the ground. Slightly elevated winds look to prevent widespread dense fog development and thus will hold off on fog headlines at this time. Trends will be monitored closely. Patchy fog is likely elsewhere, but chances for dense fog outside of the previously mentioned areas are low (<30%). Any fog should burn off by mid to late morning.

The main story to watch today will be the chance of thunderstorms this afternoon as an isolated severe storm remains possible mainly near and east of I-29. At this point, the main area to watch will be closer to the upper level support with the shortwave ejecting across the upper Midwest. This is where shear values will be the highest, mainly over far east central South Dakota into southwest Minnesota. Latest guidance is showing perhaps a bit better elevated instability collocated with this area of higher shear this afternoon. Will increase the hail size threat to ping pong balls to account for this as some elevated supercell structures may develop in these areas.

The chance of surface based storms has further diminished given models holding onto a surface cap, likely due to the cloud cover expected through much of the day today. However, if there ends up being less clouds than expected, more heating could result in very isolated surface based strong to severe storms. Main concern with this will be over northwestern Iowa and far southern Minnesota where 60 mph wind gusts will be the main threat in any surface based storms, along with hail to half dollar in size. All that said, currently thinking the better chances for severe weather will be east of the area where the stronger low level jet will be located, but be sure to keep an eye to the sky this afternoon! Timing for an isolated severe storm is between 1 pm and 8 pm.

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 /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1216 PM CDT Wed Oct 28 2026

A cold front moves into the forecast area this afternoon, progressing from northwest to southeast through the rest of the days today. Out ahead of teh cold front for the next couple of hours, expectations are for coverage of showers to weak thunderstorms to expand. The greatest chances for storms will be into southwestern Minnesota, but confidence is not high enough in thunderstorms developing over the TAF sites to include a thunder mention in the TAFs. Have included a TEMPO group for showers at KFSD and a PROB30 group at KSUX (as confidence is a little bit lower there) to capture the rain shower potential.

Otherwise, low stratus deck remains in place, and ceilings as low as LIFR have been observed. As the front moves through, ceilings will gradually improve, gradually clearing out late this evening into tonight. Behind the front also comes a wind shift to the northwest this evening, with winds becoming light and variable as a high pressure center moves overhead. With the clearing, low winds, and high humidity overnight, there is some signal for fog development early Thursday morning. Model coverage appears somewhat scattered at the moment, so confidence is again not quite high enough to intorduce reduced visibilities into the TAFs just yet. However, category reductions to IFR or lower due to visibility will be possible.

FSD WATCHES/WARNINGS/ADVISORIES

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