textproduct: Sioux Falls

KEY MESSAGES

- Strong to severe storms look to return to the area tomorrow (Tuesday) between 6 pm to 2 am. Large hail up to the size of golf balls, damaging winds to 70 mph, and an isolated tornado are the main hazards. Some uncertainty regarding storm mode remains.

- Near to above normal temperatures look to continue through this week. Confidence continues to increase in further increasing temperatures and humidity for the end of this week and weekend.

- Low chances (15-30%) for rain will accompany the end of week increasing heat and humidity.

DISCUSSION

Issued at 245 PM CDT Mon Aug 31 2026

Sunny and warm conditions persist this afternoon as temperatures have warmed to 80s. With a cold front now southeast of the area, dew points have lowered to 50s and 60s. Still seeing heat indices up to 80s to low 90s, so some humid conditions remain though not as humid as what we saw this weekend. A weak low level jet (LLJ) is expected to develop tonight which will develop showers and potentially an isolated thunderstorm across Nebraska. These showers will push east/northeastwards into a worsening environment. They could still be capable of lightning though not expected to be strong nor severe. Low temperatures will remain quite mild overnight, with lows only falling to the 60s.

The showers will push through the area during the morning to early afternoon hours. This will leave the rest of the afternoon on the dry side of things. With some cloud cover remaining aloft, highs look to remain warm but be slightly cooler than Monday's highs with temperatures in the 80s up to about 90F. Chances for severe storms begin to increase after 6 pm as a shortwave trough ejects out of the Rockies and into the Northern Plains. The previously mentioned front will begin to return northwards as a warm front due to the mass response from the wave. A sufficient warm sector will be in place ahead of the boundary with dew points in the 60s to 70s. Some capping will be in place which may limit the extent of convection early on. Latest hi-res guidance continues to show moderate variance but is beginning to show a consensus of storms developing across central and north central Nebraska and possibly south central South Dakota. These showers and storms will push into the area during the evening timeframe but the remaining uncertainty revolves around storm mode. Think a custer of storms is possible with embedded multi- cells to even supercells. As the storms push further into the forecast area, they will become more elevated due to increased capping over the area. Storm mode becomes more questionable here as storms may remain a bit more discrete to perhaps remaining in a cluster. Or if they can congeal cold pools properly, upscale growth into a line is possible. Tough to say which storm mode is correct at this time. Aside from capping, sufficient elevated instability will be in place with CAPE values up to 1,000 J/kg to 2,000 J/kg with effective shear values between 40-50 knots. Thus, damaging winds to 70 mph and golf ball size hail will be the main hazards. If a storm is able to tap into the boundary layer, then an isolated tornado will be possible. Especially if the surface warm front can push into the forecast area. The storms will push through the area through the evening and at least the first half of the overnight hours before pushing eastwards with the veering low level jet.

The daylight hours on Wednesday look to be a quiet as subsidence prevails on the backside of the departing wave. Highs will remain consistent in the 80s to even low 90s in a few locations. The break from rain will be short lived though as another shortwave trough will be pushing into the Plains Wednesday night. The ensembles support this as they show increasing probabilities up to a 20-50% chance for rainfall totals to exceed a tenth of an inch. The ensembles have the highest chances for rain east of I-29. Some elevated instability looks to be available, suggesting that thunderstorms will again be possible. Whether they will be strong to severe is uncertain at this time.

Upper level ridging will be strengthening aloft for the end of this week and weekend. High temperatures look to not only remain above average but further warm as the ridge becomes more pronounced aloft. The ensembles not only support this ridge developing, but also 850 mb temperatures being pushed to the the 99th percentile of climatology. The Euro Extreme Forecast Index (EFI) further supports this as it shows 60-80% of its members suggesting above average temperatures are possible. Humid conditions look to accompany the above average temperatures as the ensembles show a broad 50-90% chance for heat indices to exceed 90F. Chances for rain are possible (15-30% chance) during this period of time but details are highly uncertain. There are some signals that this pattern could begin to break down next week. However, medium range guidance continues to show increasing variance in this potential. Something to watch to see if these conditions will persist into next week.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1225 PM CDT Mon Aug 31 2026

Mainly clear skies and light and variable winds begin the TAF period. Cloud cover will increase aloft late this evening and night. Some light rain showers are possible near highway-20 during the morning hours tomorrow. Visibilities and ceilings are expected to remain VFR in the showers. The light rain showers and light and variable winds will finish out the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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