textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and an isolated thunderstorm or two should develop over the next hour or two near the James River Valley. An isolated severe storm will be possible. Scattered showers and storms after about midnight should not be severe.

- Strong synoptic winds are currently being observed behind a cold front that is passing through the area. Gusts up to 35 to 45 mph will continue behind the front through about 1AM before weakening. The strongest gusts will occur along and west of the James River.

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

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

UPDATE

Issued at 921 PM CDT Mon Aug 3 2026

We're beginning to see elevated post frontal showers push into the forecast area this evening. Latest hi-res guidance has been trending a touch later with the convection development. Now looking to be closer to 10PM to 11PM before sufficient storms develop. The environment remains favorable for an isolated strong to severe storm or two. Elevated instability values remain sufficient at 1,000 to 1,500 J/kg while effective shear magnitudes remain at around 40 knots. The storms look to travel more quickly than the upper wave itself which should result in the storms racing ahead of the better shear and thus allowing them to weaken below severe limits by the early overnight hours. Should a storm reach severe limits, it will be capable of large hail up to the size of a quarter and damaging winds to 60 mph. Remaining weak instability through the night will still allow a few rumbles of thunder to remain possible.

The other aspect to tonight is stronger synoptic winds in the wake of the cold front. A climatologically strong shot of cold air advection (CAA) is currently passing through portions of central and western South Dakota. All of the latest guidance shows this shot of CAA weakening as it enters the forecast area. That said, a small period of time with gusts up to 35 to 45 mph along and west of the James River is on the table from now through about 1AM before winds will weaken. Isolated stronger gusts remain possible in the passing showers and weak storms.

Still looking at showers persisting through the day tomorrow near and south of I-90. Rainfall amounts remain on track with amounts generally between 0.10" to about 0.25." Locally higher amounts up to 0.50" is also possible, though this higher QPF will be quite isolated and dependent on how the showers track throughout the day. Light rain showers look to persist through Tuesday night before exiting the area by Wednesday morning.

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 /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1101 PM CDT Mon Aug 3 2026

Showers and thunderstorms have developed along and west of the James River this evening. These showers and storms will continue to push eastwards through the rest of the overnight hours. While chances for thunder will persist, this chance will be waning through the overnight hours while scattered showers continue. Brief drops in both ceilings and visibility to MVFR/IFR levels is possible under any individual storm. Winds continue to turn to out of the northwest behind a cold front that continues to push through the area. Gusts up to 25-35 knots is expected behind the front but the strength of the winds will also be weakening through the night.

Light showers will persist through the day tomorrow, mainly near and south of I-90. Have included mention of showers in KSUX where confidence is highest in shower location. Conditions look to be VFR within the showers. Any chance for showers may come to an end by tomorrow evening. Light northwest winds with speeds up to 5 to 10 knots is expected throughout the day.

FSD WATCHES/WARNINGS/ADVISORIES

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