Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 290248 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 948 PM EST Sat Nov 28 2020 .SYNOPSIS... Dry high pressure will briefly return through tonight. A strong low pressure system approaching from the southwest will support a threat for heavy rainfall from late Sunday through early Monday. Northwest flow snow is expected to develop across the mountains in the storm`s wake from late Monday through Tuesday. Another strong low may cross the region at the end of the week. && .NEAR TERM /THROUGH SUNDAY/... As of 945 PM EST Saturday: Trends look good for the time being for the overnight period, so only some minor tweaks for the late evening update. Otherwise, a dry sfc high centered near the Missouri Bootheel has brought deep dry air across the upper TN Valley and southern Appalachians. Skies are virtually clear across the CWA as a result. The sfc high will migrate toward the East Coast through Sunday along with the associated upper ridge. A compact upper low crossing the ArkLaTex region will induce Gulf coast cyclogenesis in the morning; cirrus will increase ahead of this system beginning tonight. Deep subsidence will continue over our area, and while the progression of the pattern will allow southerly flow to redevelop in the low levels, precipitation chances remain near zero until late Sunday morning. Mins will be 6 to 10 degrees above normal under the cloud cover and WAA. Deepening moisture and upglide along with increasing upper divergence ahead of the approaching system will result in increasing PoPs from SW to NE thereafter. Model QPF has backed off a bit, and it looks like a more rapid increase in moisture won`t occur until late afternoon or evening; for these reasons the trend has been slowed. Following the airmass change that has already occurred, and increased cloud cover, max temps Sunday should be a few degrees below today`s readings, or about normal. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 125 PM Saturday...A busy period in store as a cold and moist dynamical system will affect the region. The op model guidance has diverged the past couple runs wrt the placement of the sfc low crossing the area as the GFS has shifted southeast and colder. Have taken this possible shift into account and lowered the expect QPF trends across the FA, much inline with WPC guidance. Not a huge difference in precip totals, but the ern zones are now avg/ing arnd 1.5 inches as opposed to 2+ inches. The srn BR escarpment will still likely see 24-26 hr totals arnd 2-3 inches. The heaviest rainfall period will be between 00z-06z Mon as upslope flow is maximized. Low level winds shift sw/ly to wly after that time and precip rates shud drop sigfntly. There could be some hydro issues in this area during the overnight period and the LMRFC has the French Broad at Blantyre reaching advisory level by Mon night. As the sfc low gets lifted NE Mon, winds will become aligned nw/ly upstream of the NC mtns and thickness levels will drop quickly. Expect a quick changeover to snow Mon afternoon and lowering snow levels thru the evening. Still looks like adv level snow abv 3.5 Kft, yet a noted Glakes fetch could make for extended and higher snowfall rates persisting thru Tue. For now, generally have 2-3 inches across the TN spine and higher ridges, with higher amts across the Smokies. Winds will pick up during this timeframe as well and llvl CAA flow will make for gusty conds across the higher elevations. Not seeing anything too dramatic in the soundings to suggest much more than adv level winds. There may be a brief window across the srn zones early Mon morning when enuf muCAPE interacts with stg shear levels and produces a wavy line of storms capable of producing damaging winds. The latest SPC Day 2 outlook maintains a marginal risk in the area so we will keep the mention going in the briefing package. However, confidence is low as soundings indicate a stg llvl CAP in place, which may not be overcome by the increased large scale lift. Max and min temps will remain below normal thru the period. Mon night will see lows arnd freezing over the non/mtns and m20s mtn valleys. Max temps Tue will also be held quite low, or abt 15 degrees below normal. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 200 PM Saturday: No major changes were made to the going fcst. The op models still have disparaging solns with a possible large scale upper low developing anywhere from the srn Plains to the Glakes region by late in the period. This has made for vastly different thermal and moisture fields associated with the varying sfc pressure patterns, thus precip chances will be maintained in the low chance range. Otherwise, broad hipres looks to build across the region Wed and cutoff any lingering upslope snow showers across the wrn NC mtns. This high shud keep conds dry over the fcst area with temps remaining a little below climo each day. Fri is uncertain, but a moist system could approach the area. Cold air will be in place Thu night across the mtns and the higher elevations may see periods of snowfall Thu night into Fri. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... At KCLT and elsewhere: VFR to start the period, with high pressure moving into the area keeping mainly NE winds through the period, except KAVL where SE down-valley winds will prevail. MVFR to IFR conditions already developing in the CSRA and Midlands, so have added some restrictions to the KAND TAF briefly during the overnight/predawn hours tonight. Confidence isn`t particularly high because guidance is sort of 50/50 on this. Otherwise expect the high cloudiness to continue to overspread the area, with cigs gradually dropping during the day tomorrow. -RA will move in from S to N, so introduced PROB30s initially but then trended to predominant -RA everywhere NLT 23z. Cigs will drop to MVFR with the -RA and expect continued lowering beyond the end of the period. Outlook: Continued precipitation and restrictions are expected Sunday night and part of Monday as strong low pressure crosses the region. Behind this system, wintry precipitation will be possible in the mountains later Monday into Tuesday with VFR returning elsewhere, lasting through midweek. Confidence Table... 02-08Z 08-14Z 14-20Z 20-00Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 94% KAVL High 100% High 100% High 100% High 94% KHKY High 100% High 100% High 100% High 100% KGMU High 100% High 100% High 100% High 94% KAND High 93% Low 54% High 100% High 98% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables are available at the following link: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...TDP/Wimberley SHORT TERM...SBK LONG TERM...SBK AVIATION...TDP is the U.S. government's official web portal to all federal, state and local government web resources and services.