Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 280753 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 253 AM EST Sun Feb 28 2021 .SYNOPSIS... A warm front will lift northward across the region today. A cold front will approach the southern Appalachians from the northwest tonight and then cross the area on Monday. Dry high pressure will build over from the north as the high center moves from the Great Lakes to the Mid-Atlantic coast Monday night into Tuesday. Unsettled weather returns from the west Tuesday night into Wednesday morning. Another low pressure system may affect the southeast Friday into Saturday. && .NEAR TERM /THROUGH TONIGHT/... The main concern/challenge over the early part of the fcst will be the persistence and possible extra development of dense fog across the non/mtns. A llvl ridge is trapping moisture at the sfc over the NC zones, but some improvement in vsby is noted arnd CLT. The Upstate areas within the DFA are experiencing intermittent patchy dense fog, which may become more widespread toward dawn. Wont make any areal changes to the DFA at this time and keep the 13z expiration time when sfc heating is expected to increase BL mixing. The forecast area will remain in a sw/ly flow regime this afternoon and evening ahead of an approaching cold front. Good mixing will enable low-end gusts with moderate gusts likely across the higher mtn elevations persisting thru the overnight period. A look at theta charts indicate weak isent lift ahead of the front coupled with low-end available moisture. So, think the best relative chance of light rainshowers will occur across the srn NC mtns and BR escarpment in mech lift throughout the day. The front will take it/s time reaching the NC mtns, likely aft 08z, when stronger sfc forcing and a llvl jet begin to generate higher precip rates over the wrn NC mtns. Not anticipating any hydro threats thru the near term period, but the lingering rainfall into the short range may create isol and minor flooding over the far srn NC mtns, mainly in wrn Graham Co thru late morning Mon. Max temps will increase again today in moderate llvl WAA flow. Highs should reach the mid to upper 70s over the far srn zones to the l70s north. The mountain valleys will reach the u60s to arnd 70 F. Mins tonight will also remain well abv normal with readings likely ranging from the l50s over the mtn valleys to the u50s south of the I-85 corridor. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... As of 235 am EST Sunday: A progressive northern stream trough will cross the eastern U.S. on Monday, steadily pushing the passing surface cold front south of the region through the day. Anticipate mainly morning rainfall along the passing frontal zone, with precipitation rates and coverage decreasing as the moisture exits the lower Piedmont during the afternoon. Brief upslope showers could also linger into the afternoon along the TN border counties, but still anticipate that basins can handle the event without any flooding of note, so no Flood Watches are expected at this time. Temperature trends will be hard to pin down Monday with the fropa. Expect falling mountains temperatures through the day there in the post fropa cold advection, but with a modest Piedmont spike in midday temps with downslope warming and drying east of the mountains. Deep-layer drying will continue from the northwest Monday night as the surface boundary settles off to the south. A southern stream closed upper low over the southern Plains Monday night will lift eastward through the lower MS River Valley on Tuesday. Meanwhile, surface high pressure moving from the Midwest to New England will permit cooler and drier air to spill southward into the region on Tuesday. Upglide moisture could begin to return to our region through late Tuesday. As forcing and better moisture with the southern stream system reach the southern Appalachians Tuesday night, mixed precipitation types may develop over the mountains, especially at onset of the steadier precipitation. Profiles over the high terrain suggest that snow may develop along the ridges Tuesday evening, with ptypes transitioning to more of a mixed bag overnight into Wednesday morning. The forcing and moisture should move east of the forecast area by early Wednesday as the associated surface low passes through Midlands of SC toward the NC coast. An HWO mention for the mixed ptypes could be needed for the NC mountains for Tuesday night/Wed morning. Temps should rebound at least a category on Wednesday afternoon with better insolation returning. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 245 am EST Sunday: Deep-layer northwest flow and modestly building heights will set up Wednesday night through Thursday ahead of yet another southern tier closed low pressure system moving east across Texas during the period. Temperatures will rebound again into the 60s east of the mountain by Thursday afternoon. The latest GFS solution has trended toward the ECMWF camp of opening up the southern stream system across the lower MS River Valley and Deep South and bringing more modest forcing through the southeast Friday night. Recent runs of the GFS have trended drier with this late week system, but will keep solid chance PoPs going in a nod to the wetter, more consistent ECMWF solutions. The ECMWF 850 mb and surface low center tracks would be interesting for northern tier snow potential, but this remains a long way off so no HWO mention will be made for now. Saturday will be the chilly day of the extended forecast, but with other days within a category or so of climatology. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... At KCLT: Dense fog and VLIFR conds will persist at KCLT this morning as a shallow llvl ridge has setup within highly moist sfc layer. Not anticipating much improvement until after sunrise into mid morning when the BL warms, but there shud be a quick transition to MVFR or VFR arnd 16z when gusty conds and increasing llvl mixing commences. Winds will remain locked in sw/ly ahead of an approaching wrn bndry and the gusty conds will reduce aft 22z-23z. Elsewhere: KHKY will have the best chance of locking in dense fog and VLIFR restrictions this morning as other sites remain a little better mixed and will likely see VSBYs in the IFR to LIFR range arnd daybreak, except at KAVL where down-valley flow and lack of a shallow inversion may keep conds in the VFR to MVFR range. Low-end sw/ly gusts are likely this afternoon and will diminish after 23z. KAVL will see the best chance of precip thru 06z with a moist frontal bndry approaching the TN/NC line. Thus, a PROB30 with -shra and possible IFR restrictions are mentioned aft 02z thru the period. Outlook: Periodic flight restrictions and chances for precip are expected to linger Mon into Mon night. Drier high pressure will build back into the area Tuesday. Confidence Table... 08-14Z 14-20Z 20-02Z 02-06Z KCLT Med 62% High 85% High 100% High 100% KGSP Med 64% High 84% High 97% High 100% KAVL Med 73% High 91% High 100% High 100% KHKY Med 60% Med 77% High 100% High 100% KGMU Med 65% Med 69% High 97% High 100% KAND Med 75% Med 79% High 100% High 100% 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...Dense Fog Advisory until 8 AM EST this morning for NCZ035>037- 056-057-068>072-082-502-504-506-508-510. SC...Dense Fog Advisory until 8 AM EST this morning for SCZ001>010. && $$ SYNOPSIS...HG NEAR TERM...SBK SHORT TERM...HG LONG TERM...HG AVIATION...SBK is the U.S. government's official web portal to all federal, state and local government web resources and services.