254 FXUS63 KFSD 290554 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1254 AM CDT Mon Jun 29 2026 .KEY MESSAGES... - Areas from the Sioux City metro into much of northwest Iowa have been upgraded to an Extreme Heat Warning through this evening. A Heat Advisory remains in place from Yankton to Sioux Falls to Brookings and into southwest Minnesota today. - Isolated to scattered severe thunderstorms will be possible late this 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. Take precautions to reduce the risk of heat illness. - 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 /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1254 AM CDT Mon Jun 29 2026 Areas of MVFR-locally IFR visibility in fog and/or low stratus will be possible early in the TAF period, mainly in portions of southeast SD/southwest MN. An increasing southeast low level flow overnight should prevent fog from becoming too widespread or dense (LIFR), but trends will be monitored. Any fog is expected to improve by daybreak or shortly thereafter in response to aforementioned increasing winds, leaving VFR conditions through the remainder of the period. Winds will remain gusty through the day, with south to southwest winds gusting 25-30kt during the late morning through sunset. There is a small chance of thunderstorms developing along surface boundary after 29/22Z into this evening. While an isolated storm could impact KFSD or KSUX during the latter hours of this TAF period, confidence is too low to include TS in the TAF at this time. && .CLIMATE... Issued at 1254 AM CDT Mon Jun 29 2026 Summer heat peaks today with 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 this evening for SDZ062-066-067- 069-070. Extreme Heat Warning until 9 PM CDT this evening for SDZ071. Heat Advisory from 1 PM this afternoon to 9 PM CDT this evening for SDZ040-056. MN...Heat Advisory from 1 PM this afternoon to 9 PM CDT this evening for MNZ071-072-080-081-089-090-097-098. IA...Heat Advisory until 9 PM CDT this evening for IAZ001>003. Extreme Heat Warning until 9 PM CDT this evening for IAZ012>014-020>022-031-032. NE...Heat Advisory until 9 PM CDT this evening for NEZ013. Extreme Heat Warning until 9 PM CDT this evening for NEZ014. && $$ UPDATE...Samet DISCUSSION...08 AVIATION...JH CLIMATE...JH