FXUS63 KFSD 191728 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1228 PM CDT Tue Aug 19 2025 .KEY MESSAGES... - A few spotty showers with an occasional rumble of thunder will be possible this afternoon. - Areas of fog will build back into areas along and east of I-29 tonight. With visibilities of a mile or less possible through the morning hours on Wednesday, use extra caution when making those morning commutes. - The next round of storms is expected to move through Thursday night into Friday. Severe weather is possible, but confidence on any details is low at this time. - Warm and humid through mid-week, but cooler weather is expected this weekend into early next week. We could see lows in the 40s and highs in the 70s starting Saturday! && .DISCUSSION... Issued at 422 AM CDT Tue Aug 19 2025 Areas of fog have developed this morning mainly from east-central South Dakota into southwest Minnesota, northwest Iowa, and far northeast Nebraska. It is dense in many locations so there is a Dense Fog Advisory in effect for parts of the area until 9 am, which is when most of the fog should start lifting area-wide. Another seasonably warm and humid day is in store for us as we will be under the influence of ridging aloft due to a strengthening upper-level high centered near the Four Corners region. This should help keep the area dry for today, although some CAMs are showing isolated storm development this afternoon/evening as some guidance indicates a weak wave moving through central South Dakota into central Nebraska. We actually won't be as capped as we've been at times over the past few days, but forcing will be very weak and so I'm keeping the forecast dry for now. If there is going to be a storm that develops, it would be closer to the Missouri River in south-central South Dakota. Severe weather is not expected as bulk shear values look to be less than 20 kts. With mostly clear skies and light winds tonight, more fog is expected to develop mainly east of I-29 as temperatures drop into the mid-to-upper-60s. Wednesday is expected to be dry and warm with highs ranging from low-80s east to the low-to-mid-90s west. Heading into Thursday and Friday, a deep upper low will swing out of the Canadian Rockies and it's attendant trough will dig into the northern Plains towards the northern Great Lakes. This will be the focus for our next storm chances, mainly Thursday night into Friday morning. This will also need to be the next wave to watch for severe potential, but confidence on details is low at this time. For now, the Day 3 outlook from the Storm Prediction Center paints a Marginal Risk for severe weather over the western part of the CWA. A cold front will also swing across the area with this system, and as surface high pressure moves in behind it from Canada, we will see relief from the heat and humidity heading into the weekend and early next week. I'm talking about potentially seeing lows in the 40s and high in the 70s! Looking aloft into early next week, we'll be stuck under northwest flow, which could send some shortwaves across the area. However, the better moisture looks to remain south of the area at this time and thus we are trending towards staying mainly dry. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1220 PM CDT Tue Aug 19 2025 Mostly VFR conditions will transition to a mix of IFR/LIFR conditions this TAF period. Taking a look at satellite imagery, mostly clear conditions persist across the area this afternoon. While we should see these conditions continue into the overnight hours, can't completely rule out a stray isolated shower near KFSD this evening. Besides that, the main concern continues to be developing IFR to LIFR fog. Similar to last night, should see fog begin to build in around 08z (if not sooner) then gradually become more widespread through mid- morning. Lastly, should see light and variable winds persist for the rest of the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Samet AVIATION...05