textproduct: Sioux Falls

KEY MESSAGES

- Extreme Heat Warning through 9 PM this evening. Heat index values as high as 115 degrees.

- While details are uncertain and confidence remains low, if storms develop in the late afternoon to evening today, some may be strong to severe with damaging winds, isolated large hail and locally heavy rain possible.

- Still a good chance for highs in the 90s through mid-week in most locations. Additional heat headlines are possible.

UPDATE

Issued at 508 AM CDT Sun Jul 26 2026

Scattered high-based showers or perhaps an isolated thunderstorm will linger into the morning. This activity is expected to wane by midday, which should still allow ample heating within a very moist boundary layer. Dew points well over-performed most guidance on Saturday and see no reason why similar conditions will not be seen today. As a result, nudged NBM dew points upward slightly by blending in some ECMWF/Canadian Regional data to counteract the significant hot/dry bias seen in the GFS. This data continues to support the Extreme Heat Warning through this afternoon, and have pushed the expiration out to 9 PM as forecast heat indices remain above 100F a bit later than previously expected.

While the heat/humidity is a high confidence forecast, confidence in convective potential later today is at the opposite end of the spectrum. The main question is whether storms will form, and if so, where. Some weak consensus in development toward the Missouri River Valley in the very late afternoon (5-7 PM), with isolated to perhaps scattered activity drifting east toward northwest Iowa through the evening.

With lingering uncertainty, will keep PoPs on the low side. That said, a deep dry sub-cloud layer yields plenty of DCAPE, so any storm that forms will bring a potential for locally severe wind gusts. The warm atmosphere should limit hail growth, but isolated marginally severe hail could occur with the strongest updrafts.

The boundary which could potential trigger storms late today will drop southeast of the area on Monday, allowing less humid air to filter into the area. Temperatures will remain warm with highs in the 90s, and locations south of Highway 18 may still be humid enough in the afternoon to support heat indices above 100F. However, with the Extreme Heat Warning in place for today and some uncertainty regarding influx of less humid air on Monday, opted to hold off issuance of any further heat headlines at this time.

DISCUSSION

Issued at 117 PM CDT Sat Jul 25 2026

Heat:

Not much change as dew points in the upper 60s to mid 70s provide the area with an oppressive environment. As temperatures rise into the 90s today and Sunday, heat indices will jump to between 100-110 degrees in most locations. The hottest conditions continue to look to be along the James and Missouri River valleys.

For now Monday through Wednesday should see highs generally in the 90s but with a bit less humidity. This will keep the heat index in the 90s as well. Will have to keep an eye on the dew points trends as a few more degrees of moisture will push heat indices above 100.

A wave moving through on Wednesday will likely bring slightly cooler air into the area so the second half of the week may not be quite as hot.

Thunderstorms:

Overall a capping inversion will be in place for the area through the afternoon, so development is not expected. One exception may be in and around Gregory/Charles Mix counties where model soundings hint at possibly breaking the cap. If this can happen, an isolated storm with the potential for wind gusts around 70 mph are possible. CAPE values only running about 500-1500 J/kg with fairly weak shear, but with a very dry subcloud layer. Otherwise, development should take place west of the area and move in after about 6-8 pm. This cluster of storms will likely be a bit pulsy, but with better instability and still a fairly significant sub cloud dry layer wind gusts to 75 mph will be likely with the potential for a cold pool to develop. Hail to the size of quarters will also be possible, but wind will be the main threat. Many of the latest 12z models are jumping on this wind threat and the HRRR has been very consistent bringing this wind threat right down I-90 this evening.

Some lingering showers are possible from midnight into early Sunday morning, but are not expected to be severe and may even have trouble reaching the ground with a significant dry layer below. Still a lot of question marks regarding the severe threat tomorrow afternoon and tomorrow night. For now a significant amount of dry air in the low to mid levels should provide enough capping to avoid afternoon thunderstorm development. If a storm could develop, 2000 J/kg CAPE, 30-40 knots of deep layer shear and a significant dry layer in the lower levels would support wind gusts to 75 mph and hail to the size of half dollars. Otherwise during the later evening and overnight hours the models are really backing off on any potential for the area and keeping the isolated to scattered activity to the northeast.

A wave will move through the area Wednesday into Thursday morning and be the next chance for showers and thunderstorms. This will be the next threat for possible severe storms. The main threat for showers and thunderstorms should come on Thursday.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 625 AM CDT Sun Jul 26 2026

Spotty high-based showers will linger over portions of southeast SD this morning, more likely impacting KHON TAF site than KFSD or KSUX. Thunder threat with this activity remains very isolated and opted to not include TS mention for KHON.

Stronger thunderstorms may develop late this afternoon over northern Nebraska and perhaps into far southern SD after 25/22Z. If storms form, they could develop northeast toward KFSD or east toward KSUX this evening with a potential for erratic wind gusts over 40-50kt. However, confidence in storm chances is too low to include in the TAF at this time.

Southerly winds will occasionally gust to around 20kt from late morning through the afternoon, mainly east of a weak boundary which will bring lighter but more variable winds to areas west of Highway 81 after 25/20Z.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Extreme Heat Warning until 9 PM CDT this evening for SDZ038>040-050-052>071. MN...Extreme Heat Warning until 9 PM CDT this evening for MNZ071- 072-080-081-089-090-097-098. IA...Extreme Heat Warning until 9 PM CDT this evening for IAZ001>003-012>014-020>022-031-032. NE...Extreme Heat Warning until 9 PM CDT this evening for NEZ013- 014.