textproduct: Sioux Falls

KEY MESSAGES

- Storms may develop Friday late afternoon and evening. If storms develop, they may quickly become strong to severe. Confidence in development and coverage remains low due to strong capping potential.

- Additional chances for showers and thunderstorms return Sunday morning and continue into the middle of next week. Some storms may become strong to severe.

- Cooler conditions arrive this weekend into much of next week. Occasional shower and storm chances linger mid next week.

UPDATE

Issued at 913 PM CDT Thu Sep 10 2026

Models continue to be very agreeable that surface based convection will be hard to come by on Friday afternoon with fairly strong capping and only weak convergence along the surface front. So for now, thunderstorm chances before about 7 pm look slim. There is some agreement on increasing the LLJ from about 925mb to 850mb early tomorrow evening with convergence focusing mainly east of I-29. If the elevated cap lifting from this level can weaken enough we would likely see 1500-2000 J/kg CAPE with about 30 knots of deep layer shear. This would be enough to produce hail to ping ping ball and wind gusts to 65 mph. One other area to watch will be over parts of southwest MN. Capping may weaken enough early in the evening to allow storms to either develop or build southward into the area. Shear is a little stronger in this area with similar instability so a couple of stronger updrafts will be possible. Overall continues to look like an isolated to scattered at best scenario.

DISCUSSION

Issued at 145 PM CDT Thu Sep 10 2026

This afternoon will be dry and breezy with gusts 25-35 mph, mostly clear skies, and highs in the upper 70s to 80s. Dew points will be lower this afternoon at around 60 or less. Overall a pleasant day is in store. Overnight lows will be in the mid to upper 60s with the breezy winds continuing into Friday.

Friday will be another warm day with highs in the 80s for most of the CWA, and the low 90s west of the James River Valley. Throughout the day a narrow plume of Theta-E air will advect in from the south, along and east of Highway 81. Instability will increase along and east of the plume with MUCAPE values climbing to 1500-2000 J/kg. Modest mid-level lapse rates around 7+ deg C/km will align well with the plume of instability. Bulk shear will be 35-40 kts. With clockwise curved hodographs this set up is marginal to slightly favorable for all modes of severe weather. This is also outlined in the SPC Day 2 outlook with a Slight Risk (level 2 of 5) for severe weather. However, a few items of uncertainty keep confidence in convection initiation and coverage low. Probably the most important factor is despite the moisture advection model soundings remain dry through most of the column for areas west of I-29. Forcing is on the strong side in the form of the upper trough and surface low/cold front, but without moisture not much is going to happen besides some cumulus clouds. East of I-29 moisture return flow is better, however the environment will be strongly capped. As the whole system progresses east through the evening and into the overnight the airmass slowly saturates. But by this point the forcing should be along our eastern CWA border if not into central Iowa. In this scenario we will get very little if any convection. This is the most likely scenario at this time.

The other scenario is the better moisture return drifts farther west. Then as the system passes through we could see saturation occur sooner, and thus convection begin earlier east of Highway 81 between 4 and 7 pm, and along and east of the I-29 corridor roughly between 7 pm and 10 pm. Storms would track east and be out of the CWA roughly between midnight and 3 am Saturday. The final scenario is we are able to lift off the 850-700 mb layer and scattered strong to severe storms could develop. All this to say a very conditional environment will be in place with risks for large hail and damaging wind gusts. Though the risk is low, a tornado cannot be ruled out.

Behind the cold front overnight lows will cool into the 50s and low 60s over northwest Iowa. Through the morning hours a few isolated elevated showers are possible. Winds will become northerly and light during the day. Mid-level temperatures will fall into the teens C and at the surface highs will be slightly below average for this time of year, in the low 70s north of I-90 and the mid to upper 70s to the south. Much drier air will advect in from the north bringing dew points down to the 40s to mid 50s. Saturday will be a pleasant taste of fall.

Early Sunday morning the flow aloft becomes mostly zonal and high pressure builds in at the surface. Modest moisture return on southeast winds and WAA ahead of an approaching low amplitude wave may be enough to trigger light scattered showers and thunderstorms by the late morning to early afternoon. These are not expected to be severe but could bring rain to a larger portion of the region. Sunday evening into the overnight a strong upper trough swings through northwest of the region. An associated surface low ejects out of Colorado onto the central Plains and accelerates northeast into our CWA. Though many details are unclear at this time, some storms could be strong to severe Sunday night into Monday morning. Storms may linger into the afternoon.

Northwest flow aloft is expected for the first half of next week. At the surface highs will be closer to seasonal averages, in the 70s. Another round of storms is possible mid-week.

AVIATION /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1037 PM CDT Thu Sep 10 2026

VFR through the period. Breezy southerly winds through the period with some gusts of 35 to 40 mph likely during the day Friday. A few early morning ACCAS showers will be possible Friday morning, but confidence is low. A strong to severe storm will be possible after about 22z Friday, but confidence is low and any storms that may develop should remain very isolated. The better chances will be near and east of I-29.

FSD WATCHES/WARNINGS/ADVISORIES

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