textproduct: Sioux Falls

KEY MESSAGES

- Showers and storms progress eastward early this morning. Further severe weather risks are very low, but locally heavy rain is expected under any thunderstorm. However, the risk for flash flooding is very low as well.

- An isolated severe storm is possible this evening into the overnight, with better chances in central SD and also near and north of Highway 14. An isolated stronger storm may also develop across portions of northwest Iowa/southwest Minnesota late Tuesday afternoon.

- Seasonable temperatures through the week ahead with highs in the upper 70s and 80s, and lows in the upper 50s to mid 60s.

UPDATE

Issued at 355 AM CDT Mon Aug 24 2026

A progressive cluster of showers and thunderstorms continues to track east-southeast across southeast South Dakota early this morning. Have seen an occasional brief uptick in storm strength at the southern end of the line throughout its lifecycle, but outside of a couple of weak supercells with stronger hail cores just before/around midnight, storms have remained below severe limits. Stronger cores are producing swaths of heavier rainfall with a few personal weather station reports around 2 inches in far southern Bon Homme County. Storms looks to impact portions of the I-29 corridor, mainly south of Sioux Falls, through the morning drive time, and may have to watch the Sioux City metro for localized flooding concerns if the heavier rain rates just south of the Missouri River maintain current strength over the next 2-3 hours.

DISCUSSION

Issued at 237 PM CDT Sun Aug 23 2026

A pair of waves are affecting the area, or nearby, today. The first is moving southeast through Nebraska and is keeping any instability to the south and west bottled up. Model soundings not hinting at a whole lot of activity this afternoon, with a fairly dry and stable air mass in place.

Tonight a second wave will pass by to the north and will swing a little bit of mid level moisture into the area. As this moisture moves in, some weak elevated instability, likely 500-750 J/kg CAPE develops. This will support some scattered shower and isolated thunderstorm activity, but for now severe weather looks unlikely. A few pockets of heavier rain are also possible, but also trending downward.

Monday will see temperatures warm a bit with humidity likely to increase as well. This is in response to strengthening southerly flow as a stronger wave moves east along the Canadian border. This will increase instability, especially to the northwest of the area, and should bring scattered thunderstorms to parts of central SD and near the highway 14 corridor. With the potential for about 1000-1500 J/kg CAPE and decent unidirectional shear, and isolated severe storm will be possible in these locations. One area to watch will be near northwest IA late Monday afternoon and evening where there are some hints the cap could weaken a bit as elevated moisture advection bring some instability to that area. Low confidence, but something to monitor.

Northwest flow aloft Tuesday into the weekend will keep seasonally warm temperatures in place with highs in the 80s and lows from the upper 50s to mid 60s. Starting to see a little more consistency on the next better chance for showers and thunderstorms on Friday. The latest Canadian, GEFS and EC ensembles all indicate about a 30-50 percent chance for a tenth of an inch or more of precipitation.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1239 AM CDT Mon Aug 24 2026

Scattered showers and thunderstorms have developed in central South Dakota and will generally push east-southeastward through the rest of the night into the early morning hours today. Some lingering showers and thundershowers will continue to be possible through the rest of Monday morning mainly east of I-29 as well. Some guidance has also consistently been hinting at some MVFR stratus developing behind the main wave of showers/storms this morning mainly north of I-90. Confidence in this potential is on the lower side, but enough signals to include it at KHON.

By this evening, additional thunderstorms will develop off to our west, though uncertainty is high regarding how far storms are able to progress east into our area if at all. For this reason, opted to exclude mention of this at KHON at this time. Winds will be mainly out of the south-southeast today, gusting up to 20 kts at times. Winds will gradually diminish towards the end of the period outside of any thunderstorms.

FSD WATCHES/WARNINGS/ADVISORIES

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