textproduct: Sioux Falls

KEY MESSAGES

- Areas of dense fog will continue through mid-morning mainly across northwestern IA and the Missouri River Valley.

- Isolated showers and potentially thunderstorms will be possible late tonight into Friday morning mainly along and east of I-29. Severe weather is not expected.

- Temperature will continue to trend near to above normal into the weekend with highs mainly in the 80s to low 90s.

UPDATE

Issued at 352 AM CDT Thu Aug 6 2026

Taking a look at satellite imagery, the focus continues to be on the fog and developing stratus as it gradually expands northwestwards. As of 3 am, multiple surface-based web camera's and observation sites depict soupy conditions across portions of northwestern Iowa and far northeastern Nebraska with visibilities ranging from 1/4 mile to a mile. Upon collaboration with neighboring offices, decided to issue a dense fog advisory for most of the previously mentioned areas through 10 am. Either way, should see most of this fog begin to gradually erode with the return of diurnal heating this morning. From here, a warmer and breezier day is ahead as highs peak in the low to upper 80s with quieter conditions persisting for most of the day. Southerly surface winds will become marginally breezy with gusts between 20-30 mph expected. Otherwise, a cold front will progress through the area overnight into Friday morning. While not much isn't expected initially, some elevated instability along with a strengthening LLJ will lead to a few "popcorn" showers and potentially thunderstorms developing to start the day. While severe weather is not expected, could see this activity hang out in areas along and east of I-29 through late morning on Friday.

DISCUSSION

Issued at 137 PM CDT Wed Aug 5 2026

Today will be mostly sunny and quiet under high pressure with light winds and highs in the upper 70s to low 80s. Northwest flow aloft will bring smoke into the region from wildfires out west. The smoke is expected to remain mostly aloft and currently throughout our CWA the air quality is good. For more on air quality and to get an air quality forecast for your location please see AirNow.gov

Patchy valley fog is possible early Thursday morning as winds become light to calm. Fog is most likely east of I-29 over northwest Iowa. Any fog that forms should burn off by mid- morning. As the high pressure moves off to the east this afternoon and evening winds will become southerly. At the same time from the west an upper shortwave will approach the region, strengthening the LLJ. Overnight winds will begin to increase from the west to the east. During the day Thursday good mixing up through the 850 mb level will bring down stronger gusts of 20 to 30 mph for much of the region. Portions of northwest Iowa will remain lighter at 15 to 20 mph gusts. Conditions are expected to be dry and warmer thanks to modest WAA. Highs will range from the low to upper 80s with warmest conditions over central South Dakota.

Thursday night another subtle upper wave will pivot over the region bringing chances for showers and thunderstorms. There are a few trends we will need to monitor over the next 24 to 36 hours. A narrow band of modest moisture return looks to set up over central South Dakota, but areas to the east look to remain fairly dry. Moderate surface based instability of around 1000 J/kg of CAPE will build through Thursday afternoon over central South Dakota. However, as you move east there is an increasingly strong cap in place. Instability above the cap is lacking, so elevated convection would struggle to initiate. So while an isolated strong to severe storm is possible over central South Dakota, confidence in any strong storms making it farther east than US Highway 281 is low. If storms should form it would between roughly 6 pm and midnight.

Friday sees the return of higher dew points in the upper 60s to low 70s. With highs in the 70s to 80s it will be a bit of a muggy day. A series of subtle waves will keep low PoPs in the forecast for much of the day. A more defined wave pivots through Friday evening into Saturday morning bringing chances for more organized convection, mainly east of I-29. Periodic storm chances continue through the rest of the weekend and into the beginning of next week. However, confidence in timing, coverage, and severity of storms is low as this is the point where mid-range guidance begins to diverge.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 635 AM CDT Thu Aug 6 2026

A mix of conditions are expected this TAF period mainly due to areas of MVFR to LIFR fog. While this fog will persist over the next few hours, should it gradually dimish by mid-morning with VFR conditions returning. Otherwise, southerly surface winds will gradually increase with gusts between 20-30 mph expected. Lastly, scattered showers and thunderstorms could return overnight into Friday morning with an approaching cold front. Added a PROB30 group to KFSD with a bit of rain for the increased probabilities.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until 10 AM CDT this morning for SDZ069>071. MN...None. IA...Dense Fog Advisory until 10 AM CDT this morning for IAZ012>014- 020>022-031-032. NE...Dense Fog Advisory until 10 AM CDT this morning for NEZ013-014.