textproduct: Sioux Falls

KEY MESSAGES

- Hot conditions are expected again Sunday and likely Monday where heat indices could climb to around 100. Saturday should see a slight break from the heat as winds turn northerly behind a weak front.

- Very patchy morning valley fog is possible daily, but widespread dense fog remains unlikely. Fog could reduce visibility below two miles at times.

- Wildfire smoke is possible this weekend, with the better chances over parts of southwest MN. While lower surface concentrations are expected, any sensitive groups should begin to monitor their local air quality.

- Precipitation is very unlikely (less than 10%) through Sunday. Isolated to scattered shower and storm chances return Sunday evening and night, but confidence is low on details.

UPDATE

Issued at 825 PM CDT Fri Jul 17 2026

As of 8:00 pm CDT a weak cold front is draped from roughly Hendricks MN southwest to Chamberlain SD. There is little moisture available to produce much more than clouds. However for areas of east central South Dakota and into southwest Minnesota there may be enough moisture return in the 800-700 mb level for isolated showers and thunderstorms. We've already seen a few small showers go up and then rapidly come down. While there is around 1000-1500 J/kg of MLCAPE available, there is no appreciable shear. Severe weather is unlikely with these storms, however a few strikes of lightning and wind gusts to 35 mph are possible. This front will continue to progress southeast through Saturday morning. Saturday morning patchy areas of dense fog may form, mostly along water ways and low areas.

Winds behind the front will be northerly to northeasterly, bringing cooler air to the region temporarily. Highs for Saturday are expected to in the mid 80s to the mid-90s, warmest over south central South Dakota. An upper ridge will build through the day with a surface high pressure sliding southeast into the region. As it does so winds gradually become southeasterly Saturday night and southerly by Sunday morning. Deep mixing and WAA will result in Sunday being another very hot day with Heat Index values in the mid- 90s to low 100s. A Heat Advisory may be necessary for areas west of Highway 81, but as it is still two days out have opted to wait to issue.

Over the next few days more smoke will begin to filter into the region from the Canadian wildfires. Near surface concentration should remain low, however sensitive populations may need to take precautions. Sunday overnight into Monday an upper low over central Canada will begin to drift southeast. As it does so it will push the smoke back off to the northeast.

DISCUSSION

Issued at 1251 PM CDT Fri Jul 17 2026

A weak cool front will sag south tonight into Saturday. Moisture and forcing along this boundary are very weak, so showers and storms are very unlikely. Parts of northwest IA late this afternoon could see a spotty shower or storm as a few of the models indicate a weakening cap, but with no shear and about 500 J/kg of skinny CAPE, brief heavy rain should be the only concern.

Otherwise Saturday should see a bit of a reprieve from the heat for many with highs expected to range from the mid 80s in southwest MN to the mid 90s along the Missouri River. One concern on Saturday will be the potential for some surface based smoke from the fires across northern MN. With winds turning north and then northeast, some of this could leak into the area. For now smoke concentration look to remain fairly low.

Sunday will see a return of southerly flow and hotter conditions as upper level ridging builds ahead of a strengthening jet along the Canadian border near MT. Still some hints of elevated moisture and very weak instability l;ate Saturday night into Sunday morning which could lead to isolated showers and a very isolated thunderstorm. However, the latest model runs are drier aloft than previous runs, so confidence in this is waning. Otherwise, may need a heat advisory for areas near and west of I-29 Sunday afternoon and evening with heat indices likely above 100. Sunday night will see fairly strong southerly flow in place which will lead to very warm lows in the 70s.

Monday still has a few question marks on heat, but for areas near and south of I-90 there will again be a very good chance for heat indices of 100 or greater. This is due to that jet max to the northwest now diving southeast into the area and dragging some cooler air south. For now coverage of any showers and thunderstorms looks isolated to scattered with the better chances Sunday night into Monday evening. Frontal timing and mid level moisture will play a bog role on coverage.

Once this front sags south Monday evening, stronger northwest flow aloft will remain in place which will bring temperatures back to normal or a bit below normal for the remainder of the week. While there will likely be a couple of weaker waves during this time confidence on anything more than isolated is low.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1053 PM CDT Fri Jul 17 2026

VFR conditions are expected to prevail for the period. Winds are light becoming northerly and light behind a cold front as it works its way through the region tonight. Skies will be clear to scattered high level clouds.

FSD WATCHES/WARNINGS/ADVISORIES

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