037 FXUS63 KFSD 110908 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 408 AM CDT Mon Aug 11 2025 .KEY MESSAGES... - Areas of smoke, surface and aloft, will create hazy skies with occasional impacts to air quality through early Tuesday. Minor visibility reductions are also possible at times. - Wednesday night into Thursday morning may bring a few thunderstorms to areas north of I-90, with the better chance closer to highway 14. Severe weather risks are low. - Thursday into Saturday will see increased temperatures and dew points return, with Moderate/locally Major Heat Risk. Highs in the upper 80s to mid 90s and dew points in the 70s may result in 100+ degree heat indices for some locations. - Although uncertainty remains in details, thunderstorm chances return late week into this weekend. Pattern favors nighttime to early morning thunderstorms, with locally heavy rain and perhaps some severe storms possible. && .DISCUSSION... Issued at 408 AM CDT Mon Aug 11 2025 TODAY-TUESDAY: Main concern early this week will be another round of wildfire smoke which has filtered into the northern Plains from Canada. Latest HRRR/RRFS projections hang onto areas of smoke both aloft and at the surface through today, slowly exiting east tonight through Tuesday morning as a weak cool front pushes through the forecast area. Aside from shallow fog which is also reducing visibility early this morning, expect area visibility reports in the 3-5 mile range are generally from the surface smoke with air quality readings largely in the yellow to orange range (Moderate to Unhealthy for Sensitive Groups) as of 3 am. However, upstream air quality observations in central-northeast SD/western ND are in the red (Unhealthy) category, and will have to watch for worsening air quality and perhaps visibility as we move through the morning. Other than the smoke, today and Tuesday look to be relatively nice days with modest humidity levels for this time of year and temperatures near to slightly below normal. A subtle wave may produce some sprinkles north of I-90 late this afternoon/evening but most areas should remain dry. WEDNESDAY-THURSDAY: Rising heights aloft and increasing south winds in the low levels will allow warmer air to slowly build into the region midweek. Still seasonal high temperatures in the 80s Wednesday will warm into the mid 80s to mid 90s by Thursday, accompanied by some increase in low level humidity as well. The combination of warmer temperatures and higher dew points may push heat indices above 100F in some areas Thursday afternoon, so will have to monitor trends for possible heat headlines. Placement of the mid-level thermal ridge should keep rain chances largely north of the area, though a modest wave seen in several model solutions could brush our northern counties with some storms Wednesday night into early Thursday. At this time, the greater risk for a few strong-severe storms looks to remain north of our forecast area, but if the wave tracks a bit farther south we will have to monitor potential into the Highway 14 corridor Wednesday night. FRIDAY-SUNDAY: The heat peaks Friday, with a transition to southwest flow aloft potentially bringing us back into a more active pattern by Friday night into the weekend. Seasonably warm temperatures and abundant low level humidity will fuel ample instability, but similar to this past weekend, mid level temperatures may be too warm to allow convective development in our area during peak heating. Instead, could more likely see development to our west move east into our forecast area during the nighttime to early morning hours. Still several days away, so details regarding storm location and severe potential are uncertain. However, ensembles show precipitable water values increasing above the 90th percentile of climatology with a potential southerly low level jet through eastern Nebraska, which could support at least a locally heavy rain threat. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1052 PM CDT Sun Aug 10 2025 Wildfire smoke continues to impact the area, though most of it is now aloft and thus surface visibilities have generally been improving. Still can`t rule out some drops to 4-5 SM due to smoke through daybreak. Otherwise, patchy fog could also cause MVFR visibility restrictions early Monday morning (roughly 11Z-14Z), mainly for areas near and east of I-29. Still some uncertainty in where fog will be most dense, but enough confidence to keep MVFR fog at KSUX and VFR fog at KFSD at this time. Trends will be monitored overnight. A cold front begins to move into the area towards the end of the period, which could fire off a few showers and an isolated thunderstorm mainly north of I-90, but confidence in shower coverage and timing is not high enough to include at KHON at this time. Winds will be light and variable tonight, with winds increasing to 5-10 kts out of the south/southwest Monday afternoon. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...Samet