Area Forecast Discussion
Issued by NWS Greer, SC

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS62 KGSP 291803 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 103 PM EST Sun Nov 29 2020 .SYNOPSIS...
-- Changed Discussion --
A strong low pressure system approaching from the southwest will support widespread showers and isolated thunderstorms from this evening through Monday morning. In the storm`s wake, Snow is expected to develop in the mountains near the North Carolina and Tennessee border from late Monday through Tuesday. Another strong low may cross the region at the end of the week.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 1250 PM: Still expecting mainly just increasing cirrus over the area until this aftn. Deepening moisture and upglide, along with increasing upper divergence, will develop ahead of a shortwave and sfc low pressure now spinning up near New Orleans. Precip chances still look slow to increase until a sharper increase in moisture and forcing occurs late in the day, but cloud bases are lowering on obs over the southern CWA and adjacent parts of SC/GA, and we are beginning to see very light radar returns associated with midlevel moisture. Still thinking QPF won`t be much to sneeze at thru 00z. Sfc low will strengthen as it moves NE toward the southern Appalachians this evening, with the associated shortwave being absorbed into a deeper trough digging into the mid-Mississippi valley. Strong forcing, good upper divergence, and good isentropic lift move across the area as a result. The associated surface low moves along or just west of the spine of the Appalachians and drags a cold front into the area by daybreak. A weak in situ wedge develops ahead of the developing warm front. No major changes to the thinking on these features. The warm front does move up to at least the I-85 corridor before the cold front moves in and scours the weak wedge. Very strong shear and helicity will be associated with the strong low level jet moving in ahead of the system. Minuscule sfc-based instability, even south of the wedge boundary, remains the limiting factor. Modified SHERB (MOSH) values from NAM and GFS remain low enough ahead of the cold front that damaging winds likely will not result from any storms that fire along it. We do retain slight-chance thunder south of the wedge boundary and in some spots where there is MUCAPE atop the wedge. The fast movement of this system combined with limited instability also keeps QPF on the manageable side with generally 1 to 2 inches across the area. Can`t rule out some isolated flooding, but widespread excessive rainfall is unlikely. There will be some gusty winds, especially along and south of I-85 and the mountain ridges, but should remain below advisory level. Lows will be quite mild, 10 to 15 degrees above normal.
-- End Changed Discussion --
&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 200 AM Sunday: The short term will begin with the sfc low located around the central Appalachians while winds begin to shift to a more nwly component on the backside of the system. Some lingering rain will be in store for the first 6 hours or so of the period with the remaining moisture, but should mostly dry out every where outside of the mountains by Monday afternoon. Very small severe chance is still possible over the southeastern tier with modest MUCAPE and potent wind shear during the morning hours, but confidence remains low. SPC has taken out the marginal risk out of the cwa completely with the latest update, which leads to a downward trend for any severe development. At the very least, expect some of the activity to produce a few rumbles of thunder, especially along and south of the I-85 Corridor. QPF amounts will be the highest around the southern BLue Ridge Escarpment with values between 2-3" due to the upslope enhancement expected for this part of the cwa. Elsewhere, 0.5"-1.50" totals are expected during the duration of the event. A sharp drop in thicknesses is expected over the region once the upper low evolves over the OH Valley Monday afternoon and a quick transition to wintry precip, and eventually all snow will occur over the mountains. The quickest transition will be evident at or above 3500 ft in elevation where advisory level snow totals could be in the realm with a possible decision coming later in the day today. General snowfall amounts on the order of 2-4" will be in store for the TN-NC border and the higher peaks of the Blue Ridge and Smokies. During the same time frame, advisory level winds could develop over the same locations due to the quick influx of low-level caa and the tightening of sfc pressure gradients. Expect the snow to last into Tuesday morning before the nw-ly moisture advection retreats from the mountains and drier air advects into the area. The coldest temperatures so far this season will occur during the latter half of the short term as the upper low sets up shop over the East Coast through Tuesday night and keeps the lower thicknesses over the region (<540 dm). With deep radiational cooling to go along with the low and thicknesses, temperatures will drop to around 5 degrees below normal Monday night and 10+ degrees below normal Tuesday and Tuesday night. Dry air will continue to filter in through the second half of the period with shortwave ridging gradually building in from the west and a sfc high settling over the southeastern CONUS. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 300 AM Sunday: Shortwave ridging and sfc high will settle in and control the weather pattern to start out the medium range. Expect this trend to stick around through Thursday before more changes take place just in time for next weekend. Model guidance are in agreement with swinging a longwave trough across the central CONUS while tracking southeastward towards our region by Friday. The GFS has a much broader upper low that sets up shop over the East Coast during the weekend and brings an unsettled pattern, while the ECMWF has a more confined, but potent upper low that plows into the Deep South and Southeast. The Canadian model is very similar to the GFS and produces a potent low pressure system over the area between day 5 and 7 with possible nw-ly snow on the backside for the mountains. A lot more questions than answers at this point, but something that should be monitored for now. Temperatures begin to rebound by Wednesday compared to the short term with readings climbing back to slightly below- to near-normal values. Expect this trend to continue through much of the extended, especially with the uncertainty of the system that`s expected to enter the region during the upcoming weekend. Low-end PoPs are in the forecast for much of the second half of the extended. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
At KCLT and elsewhere: Cirrus will be seen thru this afternoon, with low VFR then MVFR cigs pushing in generally S to N during this time as low pressure approaches from the SW. Deeper moisture will follow, and IFR to LIFR cigs will set in soon after steady precip arrives, as CAD forms. Mainly LIFR is expected overnight within this pattern; chances for SHRA peak overnight as low tracks across the southern Appalachians. Can`t rule out isolated TSRA forming either above the wedge or along its southeast periphery, but likely too isolated to mention in TAFs. Likewise, LLWS could occur atop the wedge but too hard to pin down to warrant mention. There remains some question as to how fast cold front will scour out low clouds and precip in the early part of the day. Even if precip ends as early as suggested by convection-allowing models, it may be hard to erode the restrictive cigs. Have included PROB30 at all sites except KAND to reflect the possibly lingering restrictions at that time. Scattering and VFR should return by midday. KAVL will begin to see clouds associated with NW flow over the mountains by midday; periodic restrictions from these may develop later in the day. Brisk wind gusts will develop in the late overnight around the region, and these will continue/strengthen as winds flip to W or NW behind the front. Outlook: Conditions improve Monday as the cold front crosses the area, but windy conditions develop. Behind this system, wintry precipitation will be possible in the mountains later Monday into Tuesday, with VFR elsewhere. VFR all locations by midweek. Confidence Table... 18-24Z 00-06Z 06-12Z 12-18Z KCLT High 97% Med 74% High 84% High 85% KGSP High 95% High 88% High 84% High 80% KAVL High 91% High 89% High 95% High 85% KHKY High 100% High 88% High 93% Med 78% KGMU High 88% Med 79% High 84% High 82% KAND High 88% High 80% Med 76% High 84% 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
-- End Changed Discussion --
&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...RWH/Wimberley SHORT TERM...CAC LONG TERM...CAC AVIATION...Wimberley

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.