227 FXUS63 KFSD 181726 AFDFSD AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 1226 PM CDT Fri Sep 18 2020 .SHORT TERM...(Today and Tonight) Issued at 358 AM CDT Fri Sep 18 2020 A clump of highly underforecast broken mid-level cloudiness continues to fester across the area early this morning, as a weak PV lobe shears out while slipping slowly southward with a decent amount of baroclinicity in place. Still quite dry at the lowest levels, and without any mentionable instability in or near the cloud layer, not likely to see any precipitation develop in the shallow and capped cloud layer. Clouds could be a bit difficult to fully remove today in some areas south of I-90. Otherwise, one more seasonally cool day today, as the sprawling surface ridge moves from northern MN into the western Great Lakes. An east to southeast gradient will be on the increase through the day, with some winds from the James River valley westward reaching a gusty 15 to 25 mph by midday. Lowest RH will be toward southwest MN/northwest IA with air exiting the ridge, but should have relatively lighter winds compared to further west as well, and the inversion with some smoke above looks to minimize threat that could mix a whole lot lower, so fire danger today does not trend too significant. Southerly winds steady out, then should get a nudge upward through the night. Upper ridge building over as some better mid-level frontal forcing develops across southeast SD with strengthening mid- level warm advection. Heights building aloft likely enough to discount any potential mid-level lift forcing with warm advection, so kept forecast dry tonight at this point. NAM and a couple of high- resolutions solutions start to pick up on the tell-tale pressure troughing downstream of the Buffalo Ridge, which suggests at least a small wind enhancement later tonight/early Saturday. .LONG TERM...(Saturday through Thursday) Issued at 358 AM CDT Fri Sep 18 2020 A kick back into more later summer temperatures commences Saturday under the ridging aloft. Even stronger south winds are likely, with some gusts as high as 35 mph. Smoke gathering again to the west in ridge axis will press eastward to thicken daytime filtering, and also should see a late day push of cirrus into central SD. Likely enough insolation to get temps into the 70s east to lower 80s west, even with potential thicker clouds and smoke aloft. Warming trend continues into Sunday with pretty much a repeat of strong southerly winds, even a bit stronger toward SW MN and the Iowa Great Lakes. While fire danger will be a bit enhanced, any cured crop areas will present a higher threat for fire than most surrounding grasses. Wave currently in the eastern Pacific will crash through the Pacific northwest tonight, and move east and lifting northeast passing north of the area later Sunday into Sunday night. Tail end of the QG/jet forcing brushes into the area Sunday into Sunday night, but by far any decent dynamical lift forcing will stay north of the area toward eastern ND/northern MN. A few high-based showers/storms could move into areas west of the James River with initial wave, on edge of cooling temps aloft. At this point, consensus is any frontal boundary is likely to wash out with any approach into the immediate area on Sunday or early Monday, so kept generally quiet with exception of another chance for thunderstorms east of I-29 late Sunday night/Monday morning with right entrance region. Monday, with somewhat more of a westerly component just off surface, temps will be near to a bit warmer than Sunday. Broad ridging takes control through Tuesday, waiting until Tuesday night to reorganize the frontal boundary to the west with next approaching wave. A bit stronger dynamical punch to this wave in terms of knocking down the ridge, so likely to best of the meager precipitation chances in the forecast from late Tuesday night through Wednesday. Even with the overheating problems with GFS, the off-surface temps anomalies in the ensemble suggest a continuation of above normal temps mid to late week, with consensus of a strong ridge back over the Plains late week. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1219 PM CDT Fri Sep 18 2020 Mid clouds lingering along/west of the Missouri River continue to decrease through the afternoon. Winds remain breezy and south/southeasterly through tomorrow, with gusts around 25 knots at times. VFR conditions are expected, although wildfire smoke continues to impact the region, with the smoke layer expected between 7k and 10k ft. LLWS is possible late tonight through daybreak tomorrow, west of the James River. Conditions look marginal at KHON, so have omitted mention from this TAF package. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && $$ SHORT TERM...Chapman LONG TERM...Chapman AVIATION...SG