textproduct: Sioux Falls

KEY MESSAGES

- Warm and humid conditions return Friday and continue through the weekend.

- A Marginal Risk (level 1 of 5) for severe thunderstorms is in place for Friday afternoon and overnight. Overall confidence in storm development is low. However, if any do develop they have the potential to produce 2 inch hail and wind gusts to 60 mph.

- Periodic shower and storm chances continue this weekend into early next week. Confidence on any details is low.

- Temperatures will be above normal this weekend into the middle of next week. Highs likely in the 90s Saturday and possibly Sunday.

DISCUSSION

Issued at 304 PM CDT Thu Aug 27 2026

One more very pleasant day today with highs in the upper 70s to mid 80s, with low relative humidity, and light winds. Outside of some thin smoke from wildfires, skies are expected to be mostly clear today and tonight. Good news for those of you who wish to catch a glimpse of the partial Lunar eclipse tonight. With one caveat.... Those in south central South Dakota have a low chance (<30%) of showers and thunderstorms this afternoon and into the evening. A subtle short wave and weak to mid-level convergence may work together to trigger convection. MUCAPE values range widely between short term guidance, from 500 to nearly 2000 J/kg and a moderately strong cap will be in place. However, steep low-level lapse rates and 35 kts of 0-6 bulk shear could support a stronger updraft or two. Risks with stronger storms is damaging wind gusts to 60 mph and marginally severe hail to 1 inch in diameter. Lows for tonight will fall to the 50s and low 60s.

Friday a few scattered storms may linger along an area of weak mid- level convergence. These should cease by late morning. Then we will see the return of higher relative humidity as southerly winds usher in a rich Theta-E ridge. Highs are expected to climb to the 80s with a few 90s sprinkled in. To the west we see a stronger mid-level wave and associated surface low pressure pushing east out of the Rockies. This will work to tighten the SPG and induce a strong LLJ through the afternoon. With good mixing we'll see gusts along and west of I- 29 in the 25-35 mph range. South central South Dakota will see the highest gusts. To the east of I-29 gusts will be 25 mph or less. As the low pushes closer a warm front will drift north through the CWA, possibly triggering showers and thunderstorms in the mid to late afternoon. Through the remainder of the afternoon and evening the system will become more compact. The LLJ ramps up rapidly through the evening and WAA intensifies which could potentially expand storm coverage and severity around midnight. A marginally unstable environment will be in place with MUCAPE values of 1000-2000 J/kg, mid-level lapse rates of 7 C/km or higher, and 35-45 kts of 0-6 bulk shear. There remains a couple of factors that keep confidence in storms low. While marginally unstable, soundings indicate a strong cap will be in place across most of the region. Without stronger forcing it is uncertain if convection will be able to initiate. However, should storms form they have the potential to rapidly become strong to severe. Risks include large hail to 2 inches in diameter and wind gusts to 60 mph.

Storms will continue into Saturday morning before pushing east of the region. The rest of Saturday looks to be dry, warm, and humid with highs climbing into the mid 80s to mid 90s, warmest over south central South Dakota. Heat Index values will be very near to critical (100 F) through the James River Valley. Sunday will be very similar, with the 90s expanded east into northwest Iowa. Heat Index values will once again be very near to critical. We will continue to monitor these trends. Sunday afternoon a cold front will move through the region, possibly bringing another round of showers and thunderstorms.

For the first half of next week the upper ridge we've been under will be squashed somewhat by a strong upper low over central Canada. Flow remains southwest with multiple short waves traversing through. This will keep shower and thunderstorm chances in the forecast through at least Wednesday.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1236 PM CDT Thu Aug 27 2026

VFR conditions are expected to prevail with few to scattered mid- level cumulus developing through the afternoon. Winds will be light and variable through early Friday morning. Then they become southerly and increase ahead of an approaching wave. Friday afternoon gusts of 20-30 kts are expected with the highest winds over south central South Dakota. East of I-29 gusts will generally be 20 kts or less.

FSD WATCHES/WARNINGS/ADVISORIES

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