textproduct: Sioux Falls

KEY MESSAGES

- 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 900 PM CDT Mon Aug 24 2026

A cold front is draped from central Canada through central North and South Dakota, western Nebraska, and into Wyoming. An associated surface trough is located roughly through the middle of North and South Dakota and Nebraska. As of 8:00 pm CDT strong to severe thunderstorms were firing along this front/trough. These are expected to slowly move east this evening with the front. As they do so they will encounter an increasingly stable atmosphere. In addition, soundings indicate a fairly dry air mass in place over eastern South Dakota. The combination of this should result in storms decreasing in intensity as they enter the western border of our CWA. Confidence in this assessment is high as current radar shows this trend. There is low confidence second scenario where the storms decouple from the boundary layer and become elevated. Should enough moisture be available at the 850 mb level, an isolated elevated storm or two could be possible. Risks with elevated storms would be marginally severe wind and hail. Most likely timing for storms is between roughly 10 pm tonight until 1 am Tuesday morning.

The front looks to slow or stall over eastern South Dakota overnight. Winds will become light and variable on either side. Around sunrise a deepening mid-level shortwave kicks the front into gear again and it begins to accelerate to the southeast. Winds behind the front will become northwest. Through the morning a weak 850 mb LLJ forms. Afternoon mixing will bring down breezy gusts between 20-25 mph with occasional gusts of 30 mph. The strongest gusts are expected to remain north of I-90 and increase as you move north. Tuesday late morning to early afternoon another shortwave works through the mid-to-upper level pattern. This potentially works to trigger another round of showers and thunderstorms. This time focused along the southern Missouri River Valley. Short term guidance is in low agreement on coverage and convective potential. Some indicate a strongly unstable environment with marginal shear that could support an isolated strong to severe thunderstorm. Others indicate a much more stable environment, but one that could support isolated to scattered showers and weak thunderstorms. We will continue to monitor the trends overnight and update details as they become clear.

DISCUSSION

Issued at 143 PM CDT Mon Aug 24 2026

Showers and thunderstorms are possible tonight into early Tuesday morning as a wave skirts by to the north and west. For early this evening, instability grows across central SD, with CAPE values of 2000-3000 J/kg, but only marginal shear. Initially storms will be most likely west of the area, but some development could creep into Gregory and Brule counties. Capping may preclude any development, so only low confidence in storms actually developing. Later tonight into early Tuesday morning a tail of convection could build south towards highway 14 and into pars of southwest MN. Here CAPE values of about 1000-1500 J/kg will be possible with minor-moderate shear. Some question as the whether we see an increase in moisture around 800 mb which appears to be needed to produce a few updrafts. Once again this is somewhat lower confidence set up. Isolated severe weather will be possible in bth areas, half dollars and 70 mph winds in central SD and quarters and 60 mph winds in southwest MN.

Warmer air aloft builds into the area Tuesday, but other than northwest IA the threat for showers and thunderstorms will be fairly low. If there is some elevated moisture there could be a little activity in the morning. Northwest IA may see just enough instability and shear on Tuesday afternoon for a couple of strong to severe updrafts.

Behind this cooler and drier air builds into the area which appears to bring dry and seasonally mild conditions for Wednesday and Thursday.

Stronger westerly winds aloft will spread across the area Friday into the weekend. This should bring occasional chances for showers and thunderstorms during this time. Friday night appears to be a better chance right now. As the warmer conditions and somewhat deeper instability build in Friday night into Saturday isolated severe storms will be possible.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 636 PM CDT Mon Aug 24 2026

VFR conditions are expected for the majority of the period. Showers and thunderstorms have developed across central South Dakota and Nebraska along a cold front. These showers are expected to travel slowly east with the front over the next 24 hours. As they do they will encounter an increasingly stable environment. In addition soundings indicate a fairly dry airmass in place. These things combined result in low confidence in storms at any of the TAF sites. However, should these storms become elevated and enough moisture advects in ahead of the front at the 850 mb level elevated strong to severe storms could be form.

Winds are currently out of the southeast and intermittently gusting up to 22 kts. Gusts will quickly decrease as daytime heating is lost, then winds will become light and variable overnight. Winds will become diurnally breezy Tuesday afternoon out of the northwest, gusting 17-22 kts.

FSD WATCHES/WARNINGS/ADVISORIES

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