FXUS63 KFSD 090212 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 912 PM CDT Wed Jul 8 2026 .KEY MESSAGES... - High temperatures remain on track to rise to the 90s to 100 degree mark towards this weekend and into early next week. - This weekend and most of next week are expected to be mainly dry. && .UPDATE... Issued at 910 PM CDT Wed Jul 8 2026 The slow moving quasi-stationary front from the past couple of days has pushed off to the southeast, taking our severe weather chances with it. Light northerly surface winds behind the front have begun to cool the boundary layer. As cooling continues an inversion will quickly set in over much of the region. This will work to trap the moisture from recent rain near the surface. As we enter the early hours of Thursday morning surface temperatures are expected to fall to, or very near to, the dew point temperatures. Patchy, dense fog is likely to develop in response, especially along and east of the James River Valley. Ensemble probabilities of visibility decreasing below 5 miles is low at around 30%. However, please ensure you are prepared for rapidly changing conditions. After sunrise winds will become northeast to east but will remain light. With little mixing occurring as a result, fog may hang on until the middle of the morning. Thursday will be dry with highs climbing to around average for this time of year, in the low to mid 80s. Thursday evening a fast moving short wave could bring rain chances to the region. Uncertainty remains high as most guidance has the storms either splitting and going around our CWA, or dissipating rapidly as they move east from central South Dakota. Overall dynamics are weak, and so if storms do form the risk for severe weather is low. Friday during the day looks to be dry and mostly sunny with highs in the mid 80s to low 90s west of the James River Valley. This weekend a strong, high amplitude high pressure ridge will build over the central United States. This ridge will persist for much of the following week. Highs during this time will be seasonably warm for July, in the 90s with a few 100s sprinkled in. Dew points will be in the 60s with low 70s possible over northwest Iowa. As we have entered peak growing season, dew points may be influenced by evapotranspiration (aka Corn Sweat), resulting in localized higher humidity. Potentially dangerous heat index values may be possible at times. Please ensure you are properly hydrated and take breaks out of the heat. The forecast for this time is expected to remain mostly dry. && .DISCUSSION... Issued at 208 PM CDT Wed Jul 8 2026 A few light rain showers persist across mainly northwest Iowa this afternoon. A surface trough and associated cold front continue to track through the forecast area early this afternoon. The mid level clouds associated with these light rain showers continue to sit over mainly northwest Iowa and surrounding locations. This has prevented locations in this area from heating out. The cooler temperatures look to also delay new convective development as the cold front pushes into this area. Still, these clouds look to clear/break up enough to allow adequate instability to develop with a magnitude up to about 2,000 J/kg over the course of the afternoon timeframe. Vertical shear values will be on the weaker side of things with a magnitude of roughly 20-30 knots. Latest hi-res guidance shows that a small, bi-modal severe weather event is on the table for this afternoon and evening. Storms look to develop on both the pre- frontal trough and trailing cold front. Storm development looks to take place across mainly northwest Iowa and adjacent areas this afternoon with a timeframe from from about 4 pm to 10 pm. With the cold frontal forcing, storms look to grow into a line as they push out of the area this evening. While vertical shear magnitudes will be on the lower side, hodographs show a weak but classic veer-back profile. With weak cold advection aloft, lapse rates will steepen just a bit more and allow for a large hail threat. Soundings do show slightly more saturated profiles in the hail growth zone (HGZ) which will tone down the hail threat a bit, with some of the largest stones growing up to half dollar size. DCAPE values will be sufficient with values up to 800 to 1,000 J/kg, keeping a damaging wind threat in place with the strongest gusts up to 65 mph. The large hail threat will come with the initial storm development before transitioning to a damaging wind threat as storms grow upscale. Pockets of moderate to heavy rainfall could result in localized ponding in low lying/urban areas as storms roll through. The storm threat will end this evening, leaving mostly quiet conditions for the overnight hours. Low temperatures will fall to the 60s. Seasonable and mostly dry conditions will return for the end of the week with high temperatures remaining in the 80s to just touching 90F. Winds will be light, making for a pleasant Thursday and Friday. Heights begin to rise aloft on Saturday, beginning to warm temperatures with highs rising to the 80s and 90s. Sunday will kick off the first day of near to above normal temperatures as medium range and ensemble guidance show a 600 dam ridge building into the Northern Plains. This ridge looks to persist through the first half of next week, brining hot and humid conditions with it. The ensembles show a 60-100% chance for highs to exceed 90F Sunday through Tuesday near and west of I-29. Chances for exceeding 100F drop to 40-70% for the same period of time with Tuesday having the highest probabilities. The ensembles also show a broad 40-100% chance for dew points to exceed 60F as well. All these probabilities to say that hot and humid conditions are expected late this weekend and into early next week. A few ensemble members show the ridge beginning to flatten next Wednesday which could begin to trend temperatures down. There remains uncertainty regarding how long the ridge remains strong so something to keep an eye on heading forward. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 626 PM CDT Wed Jul 8 2026 Strong thunderstorms have exited to the southeast of our region. A few isolated light showers will remain possible through early this evening for areas of northwest Iowa. A mix of VFR and MVFR is expected to prevail for the majority of the period. A shallow inversion has begun to form trapping moisture just above the surface. Winds decrease to light and variable after sunset and as the surface continues to cool areas of patchy dense fog are expected to form. Ceilings and visibility may drop to IFR at times in the early morning hours of Thursday. Areas along and east of I-29 are the most likely to see dense fog. Ceilings and visibility improve by mid-morning and the rest of the day will be mostly sunny with light northeast winds. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ UPDATE...AJP DISCUSSION...Meyers AVIATION...AJP