textproduct: Sioux Falls

KEY MESSAGES

- Scattered thunderstorms should develop late this evening near the James River Valley. An isolated severe storm will be possible. Scattered showers and storms after about midnight should not be severe.

- Scattered showers and non-severe, isolated thunderstorms are expected on Tuesday.

- Milder temperatures Tuesday and Wednesday with above normal temperatures Friday into the weekend.

DISCUSSION

Issued at 130 PM CDT Mon Aug 3 2026

Elevated, post frontal thunderstorms are expected to develop around the James River Valley later this evening. Timing appears to support the better chances from about 9 pm to midnight for any stronger updrafts. Assuming the models are correct with the moisture around 800-700mb behind the front, about 1000-1500 J/kg CAPE is expected with about 30-40 knots of effective shear. This may support hail to the size of quarters and with DCAPE about 1000-1500 J/kg some stronger gusts of 65 to 70 mph are possible. Of note is that the freezing level is around 14000 feet which will limit the hail threat a bit.

Tuesday will see some mid level moisture and weak elevated instability linger, which should drive scattered showers throughout the day. The better chances will be south of I-90. Amounts will not be very high, but a few locations should get 0.10" to 0.25". The widespread cloud cover and scattered showers will limit temperatures as well, with highs generally in the mid 70s.

Another wave will move by on Wednesday, with more cloud cover and rain chances near and south of roughly the Missouri River. With cloud cover and somewhat cooler low to mid level temperatures highs will again be below normal, ranging from 75 to 80 near and north of I-90 to the mid 70s south.

A warming trend will set up for the weekend as west northwest flow aloft becomes more westerly. Temperatures should climb into9 the 80s on Thursday, then mid 80s to lower 90s Friday and Saturday with some question marks for Sunday as a wave could bring slightly cooler conditions. While there is no rain in the forecast during this time, each of the models generates weak waves, with little to no agreement on when. So, as the weekend approaches, there may be a couple of brief periods when showers and thunderstorms develop.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1230 PM CDT Mon Aug 3 2026

Scattered thunderstorms will develop around the James River Valley after about 3z this evening. A few of these will be strong to severe. As they progress east later this evening and early overnight the strength should wane. Additional showers are expected throughout the day on Tuesday, with the better chances south of I-90. Outside of any showers and thunderstorms, VFR conditions are expected.

FSD WATCHES/WARNINGS/ADVISORIES

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