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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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085 FXUS63 KFSD 201131 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 631 AM CDT Sat Jul 20 2024 .KEY MESSAGES... - Unsettled weather through the rest of the weekend, with widely scattered showers and thunderstorms again Saturday and Sunday. Some funnel development may be possible Saturday afternoon along a weak surface front. - Many outdoor events this weekend will want to make sure to have an eye on the radar as activity this weekend will be rather variable in location and rapid to develop. - Cooler temperatures continue into next week, with near daily rain chances. Rain however won`t impact all locations, and will be very hit-or-miss. - Temperatures will begin to climb upwards for the second half of the week, with 50-70% probabilities of 90 degree temperatures along and west of the James River by Friday. && .UPDATE... Issued at 627 AM CDT Sat Jul 20 2024 Dense fog is will continue through mid-morning in areas along and west of I-29. Once a northerly persistent wind develops, a fairly rapid increase in visibility should take place. Will continue advisory through 14Z. && .DISCUSSION... Issued at 237 AM CDT Sat Jul 20 2024 THIS Morning: Stratus and fog continue to develop this morning under an axis of light and variable winds through the Tri-State area. There seems to be a weak surface convergence zone extending from northeast Nebraska into northwest Iowa and southern Minnesota. Water vapor imagery this morning showing a broad trough through the Upper Midwest, but it also shows a more compact circulation moving south along the SD/MN border. Lift increasing ahead of this wave should allow for redevelopment of scattered showers over eastern Nebraska and northwest Iowa through daybreak. Elsewhere, fog and stratus continues, with some potential for locally dense fog along and north of I-90. TODAY: Widely scattered showers may continue across northeast Nebraska into northwest Iowa through the morning hours. Despite the unknowns on how much ongoing stratus development clear today, isolated to scattered shower or thunderstorm development may begin to take place along a weak surface trough stretching through the Tri-State. Not a highly unstable environment with tall and very thin CAPE profiles only 500-800 J/KG on average. However NSTP and VGP parameters along the boundary indicate at least some updraft stretching potential that may result in a few brief funnels. Most of this activity should dissipate by the evening. TONIGHT: Another night of light winds may lead to fog development into Sunday morning, though perhaps there may be enough stratus around to limit the overall fall of temperatures and fog potential. SUNDAY: We`ll remain stuck with a broad upper trough over the eastern half of the CONUS Sunday. A quiet morning will giveaway to scattered shower and thunderstorm development in the afternoon and early evening as a subtle shortwave embedded in the flow moves southward. This activity is not expected to become severe, and the overall coverage only supports low PoPs at this time. MONDAY-WEDNESDAY: Scattered showers and thunderstorm risks will continue nearly every day into the middle of the week thanks to rather weak low-lvl flow but broad upper level troughing through the northern US. Most of this non-severe activity will diminish by sunset each day, but if any more sustained lobe of vorticity can develop, then activity could linger into the early overnight hours. The overall heavy rain risk remains low as PWAT values drop significantly. However any slowing storm could produce very localized 1-2" totals. Temperatures will remain slightly below normal in the upper 70s to lower 80s. THURSDAY-FRIDAY: Heights begin to rise by the middle and end of this week as ridging stuck over the Rockies and West Coast moves east. We`ll begin to see breezy southerly winds develop Thursday surging moisture back north and pushing a low-lvl thermal ridge into the Western Plains. By Friday low-lvl winds turn more southwesterly, advecting warm low-lvl temperatures eastward. Ensembles support rising temperatures into the upper 80s to 90s by the end of the week and into next weekend. ECE/GEFS all show 50-70%+ probabilities of temperatures >90+ along and west of the James river Friday, and these probabilities spread east for next weekend. Dry conditions are likely at this time. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 627 AM CDT Sat Jul 20 2024 Widespread dense fog in areas along and west of I-29 will continue for the next 1-3 hours. As stratus develops and/or a more persistent northerly wind, fog should begin to lift. However, an MVFR stratus deck may linger in place through most of the morning before lifting into VFR levels by mid-day. Very widely scattered showers may develop in portions of the Tri-state area by mid-afternoon, though coverage too limited to include in the current TAF. Should skies clear later this evening and tonight, another round of dense fog may develop into Sunday morning. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Dense Fog Advisory until 9 AM CDT this morning for SDZ038>040- 050-052>066-068-069. MN...None. IA...None. NE...None. && $$ UPDATE...Dux DISCUSSION...Dux AVIATION...Dux