textproduct: Sioux Falls

KEY MESSAGES

- Summer heat and humidity will make its return starting Sunday into next week. Heat indices up to the low 100s will lead to Major to locally Extreme Heat Risk at times. Begin planning now to reduce the risk of heat illness and impacts.

- A Heat Advisory has been issued for some areas Sunday into Monday, and further adjustments to headlines are likely in the coming days.

- A few strong to severe storms will be possible late tonight into Sunday morning. Primary risks would be up to golf ball sized hail and isolated damaging winds up to 65 mph.

- An active pattern aloft could lead to additional chances for stronger storms from early to mid next week. However, some uncertainty still remains.

UPDATE

Issued at 410 AM CDT Sat Jun 27 2026

Moist southeast flow will lead to increasing stratus across the area this morning, with some question regarding how quickly the stratus will clear and allow sufficient warming. If the clouds persist longer, high temperatures today may be a bit optimistic. However, due to low confidence in the stratus evolution, did not stray too far from the NBM projections.

While highs for Sunday have trended lower than recent forecasts, robust humidity levels combined with highs in the mid-upper 90s still lead to high confidence that portions of southeast South Dakota, northwest Iowa and northeast Nebraska will see triple digit heat indices Sunday. Lower confidence in temperatures for areas north of I-90 due to potential impacts from early morning convection, so opted to hold off on headlines across southwest Minnesota for now, though some locations there may also briefly push toward Heat Advisory criteria Sunday afternoon.

Confidence in highs on Monday are on the lower side as recent NBM forecast near the 90th percentile of the broader long-range ensemble temperatures. As a result, have nudged highs Monday down a bit across central/eastern portions of the forecast area. This still yields heat indices of 100-105F for many areas along and east of a Yankton-Sioux Falls-Marshall line. The SD/NE/IA portions of that area will see Monday morning low temperatures remaining above 75F, followed by a second day of triple digit heat indices in the afternoon, so decided to carry the Heat Advisory from Sunday afternoon all the way through early Monday evening for Yankton-Sioux Falls and points east into northwest Iowa. It's possible that this may need to be expanded north into southwest Minnesota, but given uncertainty with the temperature forecast 3 days out, opted to hold off on this for now.

Storm chances look to be focused late tonight into early Sunday morning as storm clusters move east from the High Plains after midnight. Soundings indicate a strong surface-based inversion, so primary threat from stronger elevated storms looks to be large hail in response to steep mid-level lapse rates, though warm cloud depths well in excess of 10-12kft AGL in a warming environment could limit hail sizes.

After storms exit by mid-morning Sunday, the rest of Sunday into Monday morning looks quiet. Late Monday-Monday evening could bring the next round of potential severe weather, but as noted in the SPC Day 3 outlook, this risk is conditional on storm development which is still uncertain with a moderate-strong capping inversion across the area.

DISCUSSION

Issued at 222 PM CDT Fri Jun 26 2026

CURRENTS & TONIGHT: A warm and breezy day continues! Taking a look across the area, we're continuing to see a few sprinkles to very light showers lift out of portions of far eastern SD and southwestern MN this afternoon with mainly light accumulations. While this very light activity could persist for the next hour or two, should see most of this activity push out of our area by late afternoon. From here, mostly quiet conditions will return as cloud cover thins into the evening hours. Otherwise, weak mid-level ridge will shift our quasi-zonal flow aloft back to more southwesterly overnight setting the stage for our next precipitation chances from Saturday into Sunday. Lastly, a warmer night will be on tap as overnight lows only fall into the upper 50s to mid 60s.

SATURDAY & SUNDAY: Looking into the rest of the weekend, quieter conditions will temporarily return by Saturday as weak ridging move overhead. Cloud cover will gradually increase during the day as a lifting warm front bringing in strengthening warm air advection (WAA). This combined with deeper mixing and a tightening SPG will not only lead to the return of breezy southeasterly winds, but also a slight bump in temperatures with highs peaking in upper 70s to mid 80s. Looking aloft, southwesterly flow will lead to multiple pieces of energy lifting out of the Black Hills into northeastern SD. While we can't completely rule out some isolated showers in our far northwest during the afternoon, the main concerns will develop from Saturday evening into Sunday morning as a developing triple point lifts out of the Nebraska Panhandle with a surface low. Given the slightly weaker cap and strengthening LLJ, current thoughts are that the increasing forcing with the triple point could be enough to break the cap and generate a few thunderstorms by Sunday morning.

IF storms can develop, they could become strong with a decently unstable environment characterized by around 1200-1800 J/kg of CAPE and around 40-50 kts of 0-6 km bulk shear. Stronger storms would be capable of producing up to golf-ball sized hail and damaging wind gusts up to 65 mph. Nonetheless, there are still some locational differences between short-range guidance so its a bit hard to pin down a specific area of focus right now. With all this in mind, most of our area is now outlined in an SPC Day 2 Marginal Risk (Level 1 of 5) for severe weather so make sure to multiple ways to receive warning information! From here, quieter conditions should return from late morning onwards as the upper-level ridge strengthens setting the stage for a return of dangerous heat. While the early morning storms could potentially affect our temperatures, southerly surface winds combined with a push of strong WWA aloft could boost our highs to the low to upper 90s with heat indices in the 90s to low 100s. While this would fall into our heat advisory criteria, will likely wait until things get closer to finalize any type of heat headline. Lastly, given the warmer overnight temperatures (60s- 70s); we'll have to be on the lookout for a few record warm lows across the area from Sunday into Monday (check climate section below.)

NEXT WEEK: Heading into the new week, the focus will continue to be on the heat as upper-level ridging continues to build over the eastern CONUS. With southerly surface winds in place and multiple pushes of warmer air aloft, expect temperatures to continue to hover in the low to upper 90s from Monday onwards with heat indices (Hi) in the 90s to low 100s degree marks at times. While conditions won't quite make it into excessive heat territory, we could see many areas touch heat advisory criteria (HI>100) at times each day so this will be something to watch moving forward. Either way, the conditions will lead to moderate to major heat risk for most areas from Monday through Thursday so make sure to drink plenty of water and to limit any strenuous activities! Otherwise, we'll also have to keep any eye to the skies through late week as south-southwesterly flow aloft helps ushers in multiple pieces of energy into the area through weak perturbations. With plenty of heat in the forecast, all that would be needed is a strong enough trigger to break through the cap to get something strong to severe. While the probabilities of this are low (30% or less) at this time, the chances aren't zero either so make sure to monitor you local forecast for the latest changes.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 639 AM CDT Sat Jun 27 2026

Areas of MVFR-locally IFR stratus will expand northward across the region this morning. The relatively thin stratus is expected to decrease in coverage 17Z-19Z, allowing for a period of VFR conditions this afternoon through sunset before a renewed push of low level moisture results in MVFR conditions becoming more widespread again after sunset.

Southeast winds will be more robust than recent days, with gusts 25-35kt expected from late morning through sunset. Gusts weaken only slightly after sunset thanks to a modest low level jet supporting occasional gusts around 20-25kt throughout the night.

This low level jet may trigger scattered elevated SHRA/TSRA over mainly southeast SD/southwest Minnesota after 28/06Z.

CLIMATE

Issued at 410 AM CDT Sat Jun 27 2026

Summer heat builds into the area from Sunday through much of next week. This will lead to a potential for a few temperature records to be tied, or possibly broken:

Current Record Highs:

Monday (06/29): KFSD(101|2002) KSUX(100|2022)

Current Record Warm Lows:

Monday (06/29): KFSD(77|2020) KSUX(80|1931) KHON(75|2020)

FSD WATCHES/WARNINGS/ADVISORIES

SD...Heat Advisory from 1 PM Sunday to 9 PM CDT Monday for SDZ062- 066-067-069>071. Heat Advisory from 1 PM to 9 PM CDT Sunday for SDZ060-061-065- 068. MN...None. IA...Heat Advisory from 1 PM Sunday to 9 PM CDT Monday for IAZ001>003-012>014-020>022-031-032. NE...Heat Advisory from 1 PM Sunday to 9 PM CDT Monday for NEZ013- 014.