FXUS63 KFSD 200924 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 424 AM CDT Wed Aug 20 2025 .KEY MESSAGES... - Areas of dense fog will cause impacts especially along and east of Highway-81 through 9 am. Continue to use extra caution on the roads. - Isolated to scattered strong to severe storms will be possible late Thursday into Friday. Some uncertainty remains on the overall severe potential, so keep up to date with the latest forecast. - Staying very warm through mid-week, but turning much cooler into the weekend and early next week. Highs look to be mainly in the 70s starting Saturday, with some spots dropping down to the 40s for lows. && .DISCUSSION... Issued at 421 AM CDT Wed Aug 20 2025 TODAY-TONIGHT: Areas of dense fog will continue to cause issues on the roadways this morning mainly along and east of the Highway-81 corridor, though fog should begin lifting by 9 am. After the fog dissipates, we'll be left with mostly sunny skies for the remainder of our Wednesday. It'll be another warm and humid day, with highs ranging from the mid-90s in central South Dakota to the lower-80s in the higher elevations of the Buffalo Ridge. We are looking to stay dry today and tonight as ridging aloft dominates the area. Clear skies, plentiful moisture, and light winds will once again lead to fog development tonight mainly east of I-29. Some of it could once again be dense as well. THURSDAY-FRIDAY: An upper-low will move south across southern Canada Thursday into Friday, and its attendant trough will move through the northern Plains will help set off our next round of showers and storms. At the time, a cold front will be approaching the area which will also help provide the lift for storm development. The environment by Thursday evening looks to be characterized by around 2000-3000 J/kg of MLCAPE and 35-45 kts of bulk shear, sufficient for isolated to scattered strong to severe storms to become a threat late Thursday into Friday morning. Questions remain regarding how the higher CAPE and higher bulk shear will overlap and also regarding the timing of the cold frontal passage. The best upper-level support will also be north of the area, so this could be another limiting factor to severe storm development. Showers and storms may be ongoing into northwest Iowa during the daytime Friday until the cold front finally clears the area. Temperatures on Thursday will be quite warm especially west of I-29 where compressional heating ahead of the front will coincide with peak daytime heating. Highs could climb into the upper-90s in parts of central South Dakota Thursday afternoon. The humidity won't be too impressive in these areas, so the heat index will likely stick around the air temperature through the afternoon. WEEKEND-EARLY NEXT WEEK: After the front passes, cooler temperatures are expected by Friday with highs in the upper-70s to low-80s. With continued pushes of cold air advection due to northwesterly flow aloft, it will get even cooler with highs in the 70s and lows in the 40s and 50s through early next week. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1033 PM CDT Tue Aug 19 2025 Winds will be light and variable, allowing for patchy dense fog formation, especially for areas along and east of the James River Valley. Visibility may be reduced to less than 1 mile at times. Confidence in fog formation is medium to high. KFSD and KSUX are the sites most likely to see IFR to LIFR visibilities. Fog is expected to burn off quickly as we begin to mix in the morning. Quiet conditions for the remaining part of this cycle. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Samet AVIATION...AJP