textproduct: Sioux Falls

KEY MESSAGES

- Patchy fog is expected to develop later tonight and into early Wednesday morning.

- An active pattern leads to additional rain chances on Wednesday and over the weekend. Monitor your local forecast if you have any outdoor plans, especially Wednesday afternoon as isolated thunderstorms will be possible.

- Near to above normal temperatures return from Wednesday onward with highs in the 60s to lower 70s.

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 WEDNESDAY/

Issued at 1250 PM CDT Tue Oct 27 2026

A mix of MVFR down to IFR is expected to prevail for the majority of this period. Patchy to dense fog is possible early Wednesday morning, especially for areas along and north of I-90. Brief reductions down to LIFR conditions are possible in this area. Fog may linger a bit longer into mid-to-late Wednesday morning. Visibility is expected to improve as fog dissipates, however ceilings will likely remain in the IFR to MVFR category through the end of the period.

Winds are out of the south to southwest and on the breezy side for areas along and west of I-29. Here gusts of 15-25 kts are possible, with the strongest gusts located over central South Dakota. East of I-29 gusts remain around 15 kts or less. Winds will rapidly decrease after sunset, becoming light to light and variable. Winds will become southerly through Wednesday morning, and lightly breezy again with gusts up to 20 kts.

FSD WATCHES/WARNINGS/ADVISORIES

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