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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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593 FXUS63 KFSD 200740 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 240 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. && .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 /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1031 PM CDT Fri Jul 19 2024 Fog and stratus are expected to develop tonight as winds continue to become light. MVFR to IFR conditions are expected with this development. Less certainty near KSUX into northwestern IA where showers may redevelop overnight into early Saturday, so went with rain over fog in prevailing. Stratus continues into Saturday evening especially along/east of I-29 with low pressure pivots off to the east. Uncertainty continues through the TAF period with isolated to scattered convection into Saturday night. 20.00z models are becoming a bit more isolated with coverage for areas north and west of KFSD, so narrowed and delayed PROB30 group for KHON. Showers and storms could produce locally heavy rain, reducing visibility to MVFR or IFR conditions. Above the stratus, thicker wildfire smoke is expected over the area through the period. This should remain aloft, around 20kft or higher. Winds shift to easterly toward Saturday afternoon. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Dux AVIATION...SG