


Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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427 FXUS63 KFSD 071918 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 218 PM CDT Mon Jul 7 2025 .KEY MESSAGES... - Scattered convection is likely to develop after 2pm this afternoon and continue into mid-late evening. Isolated to scattered severe storms remain possible. - Primary hazards in convection will be golf ball size hail (initial development) and winds locally to 70 mph. - Mesoscale storm cluster likely to develop Wednesday night, but a high deal of uncertainty on where this cluster of storms will track precludes higher heavy rainfall confidence. - Greatest storm chances into the weekend focus around Thursday into Friday. Mixed storm modes could bring a variety of severe weather risks, but slow storm motion may also bring locally heavy rain risks. - Trends favor drier and slightly cooler weather into the weekend. && .DISCUSSION... Issued at 212 PM CDT Mon Jul 7 2025 THIS AFTERNOON/EVENING: Mid-lvl vorticity associated with a minor trough passages continues to move through the Dakotas. At the surface, satellite and observations show an area of surface convergence situated along a line from Huron toward Gregory. Along and ahead of this boundary, we`ve seen gradual warming but perhaps not to the degree mesoscale models initially indicated. As we lose inhibition by mid-afternoon, we should begin to see isolated to scattered convection form along these convergent boundaries. NSE soundings and areas downstream indicate 1500-2500 J/KG MLCAPE, but only modest 25 to 35 knots of effective shear initially. Shear will begin to increase late in the event, but the strongest mid-lvl winds reside behind the passage of the upper trough. The end result could be a mixed presentation of scattered multi-cell clusters and very isolated supercells. Mid-lvl lapse rates remain marginal into the evening, so while initial updrafts could pose a large hail risk, the greatest potential may be from locally strong winds. DCAPE greater than 700 J/KG is focused mostly along or south of I-90, and greatest towards and south of the Missouri River. While 700 mb winds remain fairly weak (AOA 15 knots), if you can maintain some adequate updraft/downdraft balance then some linear organization of multicell clusters could form bringing a larger risks of stronger winds focused mostly south of I-90 but especially along the Missouri River into the Highway 20 corridor. The weak low-lvl flow wouldn`t suggest a great tornadic risk, though a small bit of increased helicity seems to be present along a subtle Missouri River boundary into the evening. TONIGHT: With most of this convection driven by a mid-lvl shortwave, the passage of this trough should bring convective risks lower after 10pm. It`s not impossible the 850mb LLJ tries to keep elevated convection percolating over northern Nebraska and the highway 20 corridor into early Tuesday morning, but this activity should be sub-severe. Further north, if skies clear, then some potential for fog may form into daybreak. TUESDAY: High pressure moves in for Tuesday keeping winds light and temperatures in the lower to middle 80s. Another quiet overnight is anticipated into Wednesday morning. WEDNESDAY-FRIDAY: Southerly winds return early Wednesday as low-lvl moisture returns to the Dakotas through the day. By the afternoon, one or more MCS may begin to form along a north to south frontal boundary in the Dakotas, with a very uncertain easterly track into Thursday morning. The greatest severe threat is anticipated to remain north and west of the CWA. A large discrepancy in deterministic model guidance builds into Thursday given uncertainty of MCS activity. Synoptically, the passage of a stronger mid-lvl trough would favor renewed afternoon/evening convection over the central Dakotas and Nebraska areas, with one or more MCS moving east southeast into the overnight hours. While shear will remain a bit marginal, instability should drive a severe risk at times, with strong outflow driven storms suggesting a greater wind risk. Slow storm movement and high PWAT values also would indicate a localized heavy rain risk. Confidence on placement of the heavy rain risk remains VERY uncertain with minimal signal in ensemble guidance suggesting one targeted area over another. Temperatures through the end of the week with the return of southerly flow are likely to climb back into the upper 80s to 90s with increasing humidity. SATURDAY-SUNDAY: A solution towards increased upper troughing over the Upper Midwest seems to be prevailing in ensemble guidance for the upcoming weekend. This pattern would signal cooler temperatures and lower precipitation chances. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1211 PM CDT Mon Jul 7 2025 Scattered CU field already developing early this afternoon. We`ll continue to monitor convection risks that may begin to develop as early as 2pm in central South Dakota. These scattered to broken linear line of storms may move through the TAF sites towards very late afternoon and early evening. Brief reductions in visibility and ceilings are likely in convection along with potential for 40+ knot winds briefly. Convection moves southeast late in the evening, and skies should gradually clear by morning. With light and variable winds and wet ground, some fog may be possible. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Dux AVIATION...Dux