textproduct: Sioux Falls

KEY MESSAGES

- Areas of fog, locally dense, will reduce visibility to a mile or less at times through shortly after sunrise. This is mainly expected across the higher elevations from the Prairies des Coteau to the Buffalo Ridge (east central SD/southwest MN).

- Heat indices climb to 95 to 105 today, mainly south of I-90. Locally higher heat indices are possible along and south of the Highway 20 corridor. A Heat Advisory remains in effect until 8 pm for areas south of I-90 into portions of southern Minnesota.

- Next threat for showers and thunderstorms will be on Thursday. An isolated storm could be severe.

UPDATE

Issued at 440 AM CDT Mon Jul 27 2026

Northern parts of the forecast area have seen areas of fog develop in response to light winds/clear skies allowing for optimal cooling in an abundantly moist boundary layer. Have seen occasional reports of 1/4SM visibility, mostly over the Prairies des Coteau in east central SD. Initially opted for a Special Weather Statement (SPS) due to more sparse coverage. However, webcams and satellite support more widespread coverage of the lowest visibility over the past hour, so have issued a small Dense Fog Advisory through 8 AM. Will continue to monitor and expand the advisory if needed.

Farther south, still monitoring a low potential for a few storms to develop through these early morning hours. Such activity did develop in northeast Nebraska, but has thus far remained just shy of our forecast area. This does support a low potential, though, and will maintain some low pops in our far south for the next 2-3 hours.

Otherwise the existing Heat Advisory looks good, though may have to monitor the Highway 20 corridor for a few hours above 105F heat indices midday-early afternoon before the drier air works that far south.

DISCUSSION

Issued at 118 PM CDT Sun Jul 26 2026

The thunderstorm threat is still very low confidence for late this afternoon into tonight. Quite a bit of cloud cover has lingered into the early afternoon which is slowing heating. And, as opposed to yesterday, the mid to upper level wave today is a bit weaker and may not help to organize activity as efficiently, so will need to find a way to break the cap. For now these chances look best south of I-90 into northwest IA where the deeper moisture resides. South central SD shows the weakest cap late afternoon while parts of northeast NE, far southeast SD and northwest IA see a moderately increasing LLJ during the evening hours, which could focus some thunderstorm development.

Winds turn more northerly tonight into Monday which should allow dew points to settle into the 60s and lower 70s. This will likely keep heat indices in the 90s and thus heat headlines will not be necessary. One exception may be across parts of northeast NE and northwest IA where heat indices should creep above 100 again with the higher dew points. Will have a heat advisory for these locations.

Monday and Monday night should be quiet as more stable air settles in. One exception may be later Monday night in central SD as some upper level support spreads from western SD into that area. Just some small chances west of the James for now.

Tuesday and Wednesday will be on the northern edge of the upper level ridging which will keep some westerly flow aloft in place. This should allow for a couple of weaker waves to move through. While precipitation is unlikely, some occasional cloud cover and slightly suppressed temperatures will likely keep the more extreme heat and humidity at bay, so heat headlines for both of these days looks unlikely.

A stronger wave moves into the area Thursday and should be the next better chance for showers and thunderstorms. Should see some isolated severe storms with this activity.

Temperatures settle back to near normal Friday into next weekend as northwest flow aloft should bring much more comfortable air into the region with little chance for showers and thunderstorms.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 625 AM CDT Mon Jul 27 2026

Fog coverage appears to be decreasing per satellite at the start of this period with a broad area of IFR-LIFR visibility expected to improve quickly between 12Z and 14Z. This improvement thanks, in part, to a weak boundary pushing south which will eventually spread less humid air southward across the region through the day.

The boundary will also be followed by surfacing wildfire smoke as evidenced by areas of 5-6SM visibility upstream in the drier air over north central SD. Confidence in visibility dropping to MVFR levels is too low to include visibility below 6SM in the TAFs, but patchy MVFR visibility cannot be ruled out.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Heat Advisory until 8 PM CDT this evening for SDZ050-063>071. Dense Fog Advisory until 8 AM CDT this morning for SDZ039-040- 055-056-062. MN...Heat Advisory until 8 PM CDT this evening for MNZ081-090. Dense Fog Advisory until 8 AM CDT this morning for MNZ071-097- 098. IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003- 012>014-020>022-031-032. NE...Heat Advisory until 8 PM CDT this evening for NEZ013-014.