textproduct: Sioux Falls

KEY MESSAGES

- A Heat Advisory is in effect for some areas into Monday, and further adjustments to headlines are possible in the coming days.

- Isolated to scattered severe thunderstorms will be possible on Monday late afternoon into the evening. The better chances will be near and east of I-29.

- Summer heat and humidity is expected periodically through next week. Daily heat indices of 95 to 105 degrees will lead to Major to locally Extreme Heat Risk at times. Begin planning now to reduce the risk of heat illness and impacts.

- An active pattern through the week leads to periodic moderate chances for showers and storms. Uncertainty in the timing of rain also brings lower confidence in daily excessive heat.

UPDATE

Issued at 945 PM CDT Sun Jun 28 2026

Very humid conditions continue across the area this evening, with little relief heading into tonight as temperatures remain very warm ranging from the upper 60s west to the middle to upper 70s east for lows tonight. A warm front is lifting northward into Minnesota this evening, with some showers and isolated storms developing north of the boundary. This will be occurring mostly north of the area with the exception of maybe a shower or two for the next hour or so over the Highway 14 corridor in southwest Minnesota.

Another area of storms looks to develop off to our west tonight near the Black Hills and the far western Nebraska panhandle and then track northeastward heading towards daybreak. With these storms likely forming farther west of the area than last night, it is likely that this activity misses us to our north and west. However, it can't be entirely ruled out that these storms clip the far western reaches of our area from Chamberlain to Huron and points northwest of their late tonight, after about 3-4 am. Model soundings indicate that these areas will have around 2000-2500 J/kg of elevated instability when lifting from about 850-700 mb with not too much CIN in place at times. With large CAPE profiles and mid level lapse rates around 7.5-8 C/km, hail up to the size of ping pong balls would be the threat if the core of these storms were to clip the area. Once those storms out west get more organized, should have a better idea of where they track. But as of now, chances for early morning storms north and west of the aforementioned Chamberlain to Huron line is low (<15%).

Lastly, patchy fog looks to develop in parts of the area tonight given diminishing winds and wet grounds. The best chance of this will be north of I-90 where winds will be lightest for the longest stretch of time overnight; however, high clouds from storms out to our west could help limit fog impacts overall.

DISCUSSION

Issued at 144 PM CDT Sun Jun 28 2026

Thunderstorm Risks:

Very warm and humid conditions in place today in the wake of the overnight MCS that brought a fairly widespread half an inch to 2 inches, with pockets around 3 inches. Even with the warm and humid conditions, drier air aloft and a general lack of upper level support suggest showers and thunderstorms will remain at bay. A very weak wave moves through parts of western IA tonight but moisture appears to be fairly scant with this. The more impressive wave is to the west of the area with storms looking to remain well west of the area as well.

This stronger wave pushes into central SD on Monday and brings another hot and humid day to the area. A trough of low pressure moves into the area at the surface as low pressure lifts northeast and could spark a few showers and thunderstorms. The better chances will be near and east of I-29 but once again will be fighting a bit of a cap. If storms do develop there will likely be close to 300 J/kg CAPE as well as moderate shear to support wind gusts to 70 mph and hail to the size of golf balls. Heavy rain will be a threat as well with the freezing level around 14000 feet AGL.

Tuesday night into Wednesday night may be the next period where more widespread chances for showers and thunderstorms returns. Models are fairly agreeable lifting a wave northeast into the area and only slowly exiting. This brings a somewhat extended period of warm advection in the lower levels. Instability appears to be sufficient around 2500 J/kg with weak to moderate shear. With the freezing level around 13000 feet AGL, heavy rain will also be a threat.

Another fairly well agreed upon wave ejects northeast on Thursday and may continue chances for thunderstorms. Friday into next weekend less agreed upon but continued pieces of upper level energy should move through the area bringing a continued threat for showers and thunderstorms.

Heat Risks:

Long story short, daily excessive heat is no guarantee this week given the southwest flow aloft and numerous weak waves which will likely spark showers and storms as well as produce additional cloud cover.

Monday will prove to be windy and hot with fairly high humidity. This should bring widespread heat indices of 95 to 105 to areas near and east of I-29. Heat indices west of I-29 will likely remain in the lower to mid 90s.

Tuesday will see a little drying in the low level as this Monday night wave lifts north and induces a little mixing in the low levels. While highs will again be in the 90s, lower dew points should bring a break from the higher humidity levels and likely keep heat indices in the 90s.

Wednesday will bring more question marks in regards to higher heat indices, more so the temperatures than the dew points. With the expected wave lingering around during the day, cloud cover, and possible precipitation, will bring about a lower confidence in temperatures climbing high enough to push us into more dangerous heat risk levels.

Thursday continues with a few question marks regarding excessive heat due to another wave as will Friday. Still likely daytime temperatures will climb into the upper 80s to mid 90s with some humidity, but the ability to produce widespread 100 + degree heat indices every day will be limited.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 655 PM CDT Sun Jun 28 2026

Patchy fog is likely over portions of the area tonight as winds turn lighter and the grounds remain wet from recent rainfall. The best chance of fog will be over portions of the Highway 14 corridor where winds will be the lightest for the longest stretch of time overnight. One limiting factor to fog development especially in the portion of Highway 14 near and west of the James River will be the fact that thunderstorms that develop off to our west may send some high clouds into these areas and limit cooling. That said, still enough confidence to at least add a couple of hours of MVFR conditions at KHON. Speaking of those storms, can't rule out one of those moving near the vicinity of KHON closer to sunrise, but chances for this are low (<15%) at this time.

Any fog will likely lift quickly by sunrise as winds increase area- wide through the morning hours. Winds could gust to 25-30 kts (locally to 35 kts) Monday afternoon. A low pressure system will bring a cool front into the area from west to east throughout the day Monday and turn winds from out of the southeast to out of the southwest gradually through the day. This cool front will also be responsible for isolated to scattered storm development Monday afternoon, but not enough coverage is expected at this time to warrant mention in the TAFs.

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 until 9 PM CDT Monday for SDZ062-066-067-069>071. MN...Heat Advisory from 1 PM to 9 PM CDT Monday for MNZ072-080-081- 089-090-098. IA...Heat Advisory until 9 PM CDT Monday for IAZ001>003-012>014- 020>022-031-032. NE...Heat Advisory until 9 PM CDT Monday for NEZ013-014.