Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 272343 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 643 PM EST Sat Feb 27 2021 .SYNOPSIS... A front stalled south of our region will gradually lift northward as a warm front through Sunday. A cold front will approach the southern Appalachians from the northwest Sunday night and cross the area on Monday. Dry high pressure moves from the Great Lakes to the mid Atlantic coast Monday night into Tuesday before unsettled weather returns from the west Tuesday night into Wednesday. A stronger storm system could arrive by Friday. && .NEAR TERM /THROUGH SUNDAY/...
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As of 640 PM: CAD continues to decay with scatting develop for all but the NW Piedmont and portions of the Northern Foothills. These areas will likely continue to see low clouds this evening while other areas see mainly high clouds. The subtropical ridge near the area will maintain WAA thru tonight, which will amplify as sfc cyclogenesis occurs over the Midwest. This is expected to lead to abundant cloud cover once again, likely joined by fog in the NC Piedmont and possibly the eastern part of the Upstate, where the shallow fragment of the wedge should remain. Dense fog is not out of the question given the pattern and guidance consensus. A small PoP exists overnight over much of the mountains and northern NC Piedmont via the same mechanisms; upslope forcing along the southern Escarpment and adjacent mtn ridges will further enhance chances there. Lows will be 15 to 20 degrees above normal with some locations seeing steady or even slightly rising temps. The low stratus looks likely to erode late Sunday morning, though moisture higher aloft is expected to maintain mostly cloudy conditions across the board. With the wedge finally dissolving in the morning, that should allow deeper mixing; midlevel winds will be fairly strong in the gradient between the Midwest low and the Atlantic ridge. This should result in a breezy/gusty afternoon, with temps reaching well into the 70s in many locations, a few degrees shy of records at our climate sites. RH will not be low enough for this to pose any fire danger concerns.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 205 pm Saturday: Frontal zone will be approaching the forecast area at the start of the period, then will sag southeast across the area throughout Monday. A rather vigorous precip band is expected to accompany the front across the TN Valley into the southern Appalachians, with likely-to-categorical pops forecast across the NC mtns by daybreak Monday, with high pops overspreading the remainder of the forecast area throughout the morning. Sort term model guidance continues to reveal a strong signal toward weakening of the precip region as it move across our area, as low level convergence diminishes due to disruption of the flow pattern by the high terrain, and as deeper forcing remains north of the forecast area. In fact, by early afternoon, it appears likely that there won`t be a whole lot left of the frontal band as it`s pushing east of the area. All this being the case, any excessive rainfall concerns Sun night/Monday should be confined to the areas closer to the TN border, and even there the threat appears marginal at best. Guidance continues to depict scant instability (i.e., sbCAPE < 100 J/kg) in the warm sector ahead of the front. However, the weakening forcing profiles do not support much of a high shear/low CAPE severe storm threat, nor do the shear profiles, which are rather inadequate given the paltry buoyancy. Otherwise, high temps will generally occur during the morning across the mtns, with temps steady (valleys) or slowly falling (peaks/ridge tops) throughout the day. As usual, downslope warming will offset any late morning/afternoon CAA across the Piedmont/foothills, allowing max temps to again warm to above normal...by about 5 degrees or so. The remainder of the short term will see a return to normal...if not a slightly below normal temps and dry weather. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 220 pm Saturday: A split flow regime will dominate the pattern across much of the Conus, with an active southern stream likely bringing two rounds of precipitation during the period. Fortunately, there is more of a consensus among deterministic global model guidance regarding these two events, particularly an event that is expected to unfold in the Tue night/Wed time frame, when a compact, but rather potent upper low is forecast to move across the TN and OH Valleys into the Appalachians. The GFS continues to be weaker/more suppressed with this feature, but much less so than in yesterday`s runs, giving us the confidence to bump pops into the likely/categorical range for much of the forecast area after midnight Tue night, with pops quickly tapering off from the west Wed morning. Current indications are that sufficient cool air will be left in place by retreating surface high to create a wintry precip concern across the mtns and perhaps the I-40 corridor in the foothills/Piedmont. However, the absence of any signal of a strong cold air damming event/mech to lock in cold air suggests such an event would likely be of the nuisance variety. Guidance is also in better agreement regarding potential impacts of a southern stream system later in the week, although differences remain regarding the details. Nevertheless, the GFS and ECMWF/Canadian camps identified yesterday are definitely trending toward one another, with a slightly more potent/wetter system depicted in the ECMWF/Canadian, and a much less potent/not nearly as wet and more phased flow solution per the GFS. As such, pops are warranted Friday through early Saturday, but these generally remain only in the 30-40% range. Temps are forecast to remain around, if not slightly below climo through the period, although a brief return to above-normal conditions may return Thursday ahead of the late week storm system. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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At KCLT and elsewhere: Low clouds have scattered out for all but KHKY. Expect VFR through much of the evening where it`s already in place. However, KHKY will keep IFR cigs through the evening. IFR cigs return overnight with generally MVFR vsby. Conditions then deteriorate further with LIFR to potentially VLIFR cigs before daybreak. Vsby follows similar trends. KAVL will most likely see IFR cigs and MVFR vsby as conditions there remain a little more mixed. Isolated showers also possible at KAVL. Strengthening low level winds mean LLWS develops overnight at KAVL as well. Conditions only slowly improve Sunday morning with vsby improving first but IFR cigs lingering to nearly 18Z before lifting to low VFR or even scattering out. Light and variable winds this evening and overnight become s to SW during the morning. Winds increase and become gusty for the afternoon. KAVL will see light S wind through the night with an increase in speed for the afternoon. Outlook: Flight restrictions and chances for precip are expected to return Sunday night and linger into early next week. Drier high pressure will build back into the area by Tuesday. Confidence Table... 23-05Z 05-11Z 11-17Z 17-18Z KCLT Med 78% Med 60% Low 45% Med 72% KGSP High 94% High 85% High 85% High 83% KAVL Med 66% High 90% High 80% High 94% KHKY High 89% Med 75% High 90% Med 78% KGMU High 94% High 80% High 80% Med 78% KAND High 94% High 90% High 90% High 89% 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: www.weather.gov/gsp/aviation
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...RWH/Wimberley SHORT TERM...JDL LONG TERM...JDL AVIATION...RWH

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