textproduct: Sioux Falls

KEY MESSAGES

- Scattered showers and thunderstorms will continue to progress through the area through daybreak. The severe weather risk is low but not zero.

- Warm and humid conditions continue into the weekend. Afternoon heat indices may approach 100F in portions of the Missouri River Valley Saturday/Sunday as temperatures climb into the 90s.

- Periodic shower and storm chances continue this weekend into early next week. Confidence on any details is low.

UPDATE

Issued at 256 AM CDT Sat Aug 29 2026

Taking a look across the area, we're continues to monitor lingering showers and storms north of I-90 this morning. While most of this activity is being spurred by the nocturnal LLJ, current thinking is this activity should continue to progress to the east-southeast following the mid-level shortwave through about daybreak (5am-7am) before exiting our area. While the risk severe storms is low, strong gusts between 40-50 mph and small hail up to dime size will be possible over the next few hours. Otherwise, the forecast remains on track as combination of southwesterly surface winds and lingering warm air advection (WAA) helps highs approach the mid 80s to mid 90s for the day.

With dew points in the upper 60s to low 70s expected to accompany this heat this afternoon, heat index values will creep up towards the upper 90s to low 100s with the warmest conditions along the Missouri River Valley. With this in mind, make sure to stay hydrated especially if you have any outdoor/tailgating plans this afternoon. Lastly, an active pattern aloft with usher in another shortwave from the Black Hills to northeastern SD tonight. While the strongest dynamics will likely be focused to the north and northwest of us, can't rule out pockets of isolated to scattered showers through Sunday morning with very low chances for stronger storms.

DISCUSSION

Issued at 316 PM CDT Fri Aug 28 2026

Today will be partly cloudy and breezy. Southerly winds increase through the morning as an upper shortwave and surface low pressure move in from the west. Areas along and west of I-29 can expect gusts of 20-30 mph with the strongest gusts over south central South Dakota. Here occasional gusts to 35 mph are possible. Areas to the east of I-29 will see gusts of 20 mph or less. Winds will bring in warmer temperatures and moisture, boosting dew points into the mid to upper 60s F. With highs expected to climb into the 80s and low 90s today will feel bit muggy.

This afternoon and through the overnight SPC has issued a Day 1 Marginal (level 1 of 5) Risk for severe thunderstorms that covers most of the CWA. A marginal to slightly unstable environment will develop through today with 1500-2500 J/kg of MUCAPE, 35-45 kts of deep layer shear, and steep mid-level lapse rates. However, uncertainty in storm development is high due to a couple of factors. First is cloud cover, should morning clouds linger through the day it may limit surface heating, therefore limiting instability. Guidance has some variation on the timing of the wave and amplification of the LLJ. The GFS and EC continue to have the wave and LLJ move through earlier, while the CAN and NAM are slower. Similarly, CAMs guidance is split with the HRRR, NamNest, and RAP13 showing earlier initiation while the ARW and FV3 are later. With the earlier solutions it is more likely that initial convection will begin as super cells that grow upscale into a line, possibly with bowing segments. The slower solutions will more likely begin as elevated multicell convection that grows into a line with bowing segments. As of 2:30 pm CDT a cumulus field is forming over western and central South Dakota, some producing light radar echoes. This could be an indication that the cap is weakening, thus an indication that earlier convective initiation may be the correct solution. That being said, the greatest severe risk still looks to be between 10 pm tonight through 6 am Saturday. Hazards are heavy rain, 1.5 to 2 inch hail (with supercells west of the James River Valley), and wind gusts 60-65 mph. As storm progress east they will become elevated and transition to more of a wind and heavy rain threat. Greatest risk area is along and north of I-90.

A few showers and storms may linger into mid-Saturday morning before pushing east of the CWA. Through the day the surface low associated with the previous storms will drift east, pushing clouds out of the region. Southerly winds will remain breezy gusting up to 30 mph. Warm and moist air continues to advect into the region. Highs will climb into the upper 80s to mid 90s, and dew points to the mid 60s to low 70s. Heat Index values will climb into the 90s, with areas along the southern Missouri River Valley potentially reaching 100. At this time a Heat Advisory is not necessary, however we will monitor the trends. Storm chances return for late Saturday evening into Sunday morning. Looking aloft a deepening upper trough will push east into the north central Rockies. On the east side of the mountains a subtle mid-level lee trough and surface low form. As this begins to drift east late in the afternoon along with an area of enhanced vorticity it could trigger showers and thunderstorms. A marginally unstable environment with steep mid-level lapse rates and 35 kts of deep layer shear may support isolated to scattered strong to severe thunderstorms, mainly over central South Dakota. SPC has issued a Day 2 Marginal Risk west of a line from roughly Huron, to Plankinton, to Bonesteel. For this area hazards include large hail and damaging wind gusts. As storms drift east they will encounter a less favorable environment and should weaken. Similar to Friday- Saturday, confidence in storm formation is low due to the conditional nature of cloud clearing, a strongly capped environment, and variance in guidance on storm track and timing.

Sunday brings yet a third round of potentially strong to severe thunderstorms. SPC has issued a Day 3 Marginal that encompasses the entire CWA. A marginally unstable environment is expected for the afternoon and evening. Stronger forcing this round as an upper closed low skirting the international border drags a cold front through the northern Plains Sunday evening into Monday morning. Mid- range guidance is in very low agreement on track and timing of this system. In addition, south to southwest winds for western and central South Dakota advect in a drier air mass than the previous two days. This general lack of moisture will likely prevent convection from forming over this region. At the same time over eastern South Dakota and Nebraska, and western Minnesota and Iowa moisture rich air will pool south of the warm front. As the cold front approaches this area showers and thunderstorms may form. Coverage of storms will depend on how far west the moisture rich air flows

A weak upper ridge builds in through the day Monday. A series of "ridge rider" short waves keep storm chances in the forecast nearly daily for much of next week.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 635 AM CDT Sat Aug 29 2026

Mainly VFR conditions will continue this TAF period. Taking a look at satellite imagery, we're continuing to watch showers and thunderstorms progress through portions of northwestern IA this morning. Should see conditions gradually clear by mid-morning giving way to more VFR conditions. Otherwise, southeasterly winds will become more southwesterly winds by this afternoon with gusts between 20-30 mph possible at times.

FSD WATCHES/WARNINGS/ADVISORIES

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