textproduct: Sioux Falls

KEY MESSAGES

- Hot weather continues through the weekend. Highs in the 90s to around 100 degrees expected. Dew points remain a bit below seasonal normals, aiding in lower relative humidity. However, cumulative nature of the heat could lead to some heat impacts. - Very patchy morning fog is possible daily, but widespread dense fog remains unlikely. Fog will likely be confined to river valleys and nearby areas, but could reduce visibility below two miles at times.

- Precipitation very unlikely (less than 10%) through Saturday night. Sunday into Monday chances rise to 15-25%, but confidence in timing is very low.

UPDATE

Issued at 252 AM CDT Wed Jul 15 2026

Added in some patchy and locally dense fog to the area, mainly across river valleys near and east of I-29. Through early this morning, lowest visibility as been briefly below a mile for portions of southwestern MN and northwestern IA where winds are very light to calm. Expect patchy and locally dense fog to linger through 8 AM CDT.

Made some minor changes to the temps and dew points over the next couple of days from the NBM based on trends; however, no appreciable impacts to heat index values or HeatRisk. Still anticipate highs in the 90s to near 100 through the weekend with dry conditions through Saturday. Even with slightly increased humidity, heat index values remain in the 90s today, with some locations around 100 Thursday. Continue to take precautions to limit heat and sun exposure. Know the signs and treatment of heat stroke and heat exhaustion.

For more information on the climatological context of this heat wave, please see the Climate section below.

DISCUSSION

Issued at 132 PM CDT Tue Jul 14 2026

Overall trends for above normal temperatures continues for the next several days. For Wednesday and Thursday did lower highs a couple of degrees and increase dew points a couple of degrees given latest trends/bias in the guidance. Basically the GFS is too hot and too low of dew points and that is getting incorporated into the NBM guidance and producing a trackable bias. The overall effects will not be significant as heat risks remain below advisory criteria with afternoon heat indices in the 90s.

Friday looks like it could be the hottest day of the week as a weak front settles south and some enhanced mixing becomes possible as surface winds turn more southwesterly. This should be the day with the better chance for more widespread highs from the mid 90s to 103 or so.

On Saturday, the NBM might be running too high given latest MOS and raw output as well as the bias corrected data. All point to lower temperatures. Still far enough out not highly confident on timing of this weaker boundary. On thing that could happen is the front could stall in the area and produce a little moisture pooling at the surface which would bring higher dew points. Something to watch for.

Still some hints that the upper level ridge will break down just enough Sunday into Monday to allow for some isolated shower and thunderstorm potential. This continues to be a lower confidence scenario, especially in terms of timing.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1147 AM CDT Wed Jul 15 2026

VFR through the period. Some 3-6 kft diurnally driven cumulus is expected through about sunset. Patchy fog will again be possible but impacts will be minimal.

CLIMATE

Issued at 252 AM CDT Wed Jul 15 2026

Daily record highs for our four climate sites (Huron, Mitchell, Sioux Falls, and Sioux City) are all squarely into the 100-110+ range through the next week, so not expecting any record highs. Record warm lows are in the upper 70s to lower 80s so again, not expected any records here either at this time.

Looking at the duration of the heat via consecutive 90+ degree days, we may approach the Top 10 list for some locations if 90+ degree highs remain in place through early next week. With heat looking to break into the 80s mid to late next week, we will not be anywhere close to the longest streak of 90s for any climate sites.

Longest streak (year of occurrence): - HON: 23 days (1941, 1974) - MHE: 27 days (1936) - FSD: 19 days (1910) - SUX: 27 days (1936)

To break into the top 10 list, we'd have to match or exceed the following streaks for each climate sites:

- HON: 11 days; occurred 6 times, last in 1991 - MHE: 15 days; occurred 3 times, last in 1964 - FSD: 11 days; occurred 4 times, last in 1989 - SUX: 12 days; occurred 5 times, last in 1955

Current (through Tuesday, 7/13) streaks are: - HON: 4 days; streak began July 10 - MHE: 4 days; streak began July 10 - FSD: 2 days; streak began July 12 - SUX: 0 days; last hit 90+ on July 8

FSD WATCHES/WARNINGS/ADVISORIES

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