


Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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760 FXUS63 KFSD 271124 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 624 AM CDT Fri Jun 27 2025 .KEY MESSAGES... - Fog has continued to expand for areas without stratus. Although dense fog has been sporadic, coverage has been expanding. Issued Dense Fog Advisory through 10 AM. - Periodic thunderstorm chances return late this afternoon through the weekend. Storms could become strong to severe at times. Continue to monitor the forecast if you have outdoor or travel plans. - Strong to severe storms are possible after 5 PM today, with initial development across south central South Dakota. Large hail to 2 inches and wind gusts to 70 mph are the main threats. A tornado or two cannot be ruled out. - Additional strong to severe storms are possible Saturday and Sunday during the afternoon/evening hours. - Warming temperatures and increasing humidity this weekend bring a risk of heat indices above 100F in some areas Saturday afternoon. Otherwise seasonably warm temperatures prevail much of next week. && .UPDATE... Issued at 517 AM CDT Fri Jun 27 2025 Satellite and observations - including area DOT cameras - show expanding fog over the area not covered by stratus. Although some areas of dense fog have been sporadic, issued a Dense Fog Advisory for much of south central and southeastern SD into northeastern NE through 10 AM CDT as dense fog has been increasing in coverage over the last hour or so. Will continue to monitor. && .DISCUSSION... Issued at 338 AM CDT Fri Jun 27 2025 CURRENTS-TODAY: Stratus has remained relatively stagnant this morning despite surface high pressure working into the region. Some fog is developing as of 3 AM, mostly in low-lying areas where skies have cleared. Will continue to monitor fog development in case a headline is warranted. If traveling, be prepared for quickly changing conditions and locally dense fog. Visibility may drop below one mile at times. Temperatures are starting the day in the mid 50s to lower 60s with light winds. Surface high pressure continues to move to the east through the afternoon hours with lee side surface cyclogenesis beginning across western SD/eastern WY later in the day. Surface flow shifts southerly behind the high pressure so expect highs along and west of the James River to climb into the upper 80s and lower 90s with wind gusts around 25 mph. Dew points rise to near 70 degrees in this area. Further east, lighter winds expected with highs on the cooler side in the upper 70s to mid 80s. Storms begin to develop in south central SD after 5 PM. Details below. THIS EVENING-SATURDAY NIGHT: Weak mid and upper level wave along with aforementioned surface low move east beginning this evening. Instability increases west of I-29 and into south central SD thanks to those warm temperatures and increasing dew points, with over 2500 J/kg of CAPE - some guidance near or above 4000 J/kg. Expect storms to begin to break the cap around or after 5 PM as we warm near to above convective temperatures across south central SD with the wave moving east. Guidance remains split on how far east this initial development starts; however, beginning to see more agreement this morning in the CAMs going in Todd/Mellette counties. Steep mid level lapse rates are expected, over 8 deg C/km. Bulk shear values at or above 35 knots support rotating storms. 0-1km bulk shear values at or exceeding 25 knots, although LCL heights near to above 4kft may limit the potential for tornadoes somewhat. Discrete storms may develop into clusters as they move east with low confidence on how far east storms track. Main severe threats late this afternoon through tonight are hail up to 2 inches in diameter (although some larger is possible) and wind gusts to 70 mph. Expect hail to be more of a threat with any discrete cells, and wind gusts to be more of a threat with linear storm mode. Stronger wind gusts (over 70 mph) may occur with lines of storms. There is at least a narrow window where a tornado or two are possible - especially with any storms tied to a boundary. Locally heavy rainfall is possible. For Saturday, we`ll have to wait and see where resultant boundaries from Friday`s convection end up and just how quickly we recover during the day. At least one mid/upper level wave and surface low pressure moves through the pattern late Saturday afternoon and into the night. Confidence is low in the exact timing of storm development as well as placement in potential severe weather Saturday. Greatest risk Saturday looks to be in the afternoon and evening after the atmosphere has had time to recover and warm, with temps in the lower to mid 90s and dew points in the upper 60s to mid 70s. Primary hazards are large hail and damaging winds, although storms which develop along or near a boundary could produce a tornado. Could see some localized heavy rainfall as well with stronger storms. Temperatures and dew points rise into the first half of the weekend, with more widespread 90s on Saturday. Saturday`s highs may be influenced by today/tonight`s convection, but that heat with dew points in the mid 60s to mid 70s could produce heat index values near/above 100. Will continue to monitor for potential heat headlines. SUNDAY-MONDAY: Mid/upper level trough takes shape along the International Border Sunday, moving east through Monday. This drags a front and weak surface low through the region Sunday and Sunday night as well as a couple of weak mid level waves. These aforementioned features keep shower and thunderstorm chances in the region, although scope will likely depend on how the previous days` convection shake out. Surface high pressure builds in Monday so expect a break from more widespread rain and storm chances. Not quite as warm Sunday/Monday with highs mostly in the 80s. TUESDAY ONWARD: Ridging aloft builds early in the week and slides east through mid week. Could see some isolated to scattered showers and storms mid week as the ridge breaks down somewhat and a few mid/upper waves move through northwesterly flow. Temperatures remain near to above normal in the 80s to lower 90s for highs and upper 50s to upper 60s for lows. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 616 AM CDT Fri Jun 27 2025 A few aviation concerns of note this forecast period. This morning, IFR and lower stratus remains stagnant from a KHON to west of KFSD to KSUX line and points east. Fog with visibility to 1/4 SM or less, has been observed to the west of the stratus. Some reduced visibility has been observed in the stratus deck as well. Expect fog to lift through mid/late morning. Some guidance holds on to at least patchy MVFR stratus this afternoon, but confidence is low. Keeping an eye on showers and storms across central SD as they move east. For now, will keep the forecast dry but can`t rule out some isolated to scattered activity mid/late morning west of the James River. Attention turns to the potential for additional showers and storms developing late this afternoon in south central SD and moving east through tonight. Some of these storms could be strong to severe. Given low confidence on the evolution of these storms, have left any PROB30 group out of KFSD and KSUX for now. Light and variable winds this morning increase and become southerly. Gusts to around 20-25 knots along and west of the James. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Dense Fog Advisory until 10 AM CDT this morning for SDZ050-052- 053-057>060-063>065-068>070. MN...None. IA...None. NE...Dense Fog Advisory until 10 AM CDT this morning for NEZ013. && $$ UPDATE...SG DISCUSSION...SG AVIATION...SG