285 FXUS63 KFSD 290917 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 417 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 415 AM CDT Mon Jun 29 2026 Areas of fog west of Highway 81 have become at least locally dense early this morning as light winds/clear skies allow for optimal radiational "cooling" atop moist ground from recent rainfall. Expect this to be relatively short-lived as southeast winds increase quickly shortly after daybreak. Opted to issue a Dense Fog Advisory through 7 AM, but given recent satellite trends in our south-central counties, may be able to cancel portions early. Attention also focused toward robust convection in south-central South Dakota which could brush our extreme western counties around daybreak. General storm motion to the north-northeast would keep the storms west of Chamberlain to Huron, but the deviant motion of the supercell could bring a greater threat to these areas if it maintains supercellular characteristics. Will be watching this closely over the coming hour. With regard to today's heat/humidity, opted to bump much of our northwest Iowa counties including the entire Sioux City Metro area to an Extreme Heat Warning for today. Still a bit of uncertainty in temperatures, but if readings remain slightly cooler, then dew points will likely remain higher, balancing out the potential impacts with heat indices of 105 to 108 degrees expected for multiple hours. Convective chances along the cool front late this afternoon and evening are still uncertain as some CAMs maintain a strong cap and limit development, while others are much more rambunctious with their development. Will be monitoring trends throughout the day. && .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. Dense Fog Advisory until 7 AM CDT this morning for SDZ038-039- 050-052-053-057>059-063-064. 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...JH DISCUSSION...08 AVIATION...JH CLIMATE...JH