Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 040009 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 709 PM EST Sat Dec 3 2016 .SYNOPSIS... Increased moisture will return from the west on Sunday and linger into Tuesday. A strong cold front will arrive early Thursday bringing some of the coldest air of the season so far at the end of the week. && .NEAR TERM /THROUGH SUNDAY/...
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As of 645 PM EST: Moisture return to the southern tier of the forecast area has been a bit faster than progged and the onset of PoPs will be hastened and then increased through the overnight hours. The near-term convection allowing models, including the latest and time-lagged versions of the HRRR, appear to have a good handle on this faster timing and will be followed. The 18Z models and latest RAP have warmed northern mountain and mountain valley profiles a bit for the overnight hours, but I`m hesitant to back off on the mixed precip (mainly snow) mention overnight since the wet bulb profiles remain quite cool. Will generally follow the earlier trends of increasing snow PoPs primarily along the northern Blue Ridge overnight, but any high elevation accums will be very light based on all the ensemble data. Otherwise...a closed H5 cyclone centered over NW Mexico continues to deepen as moisture lifts N/NE across the MS Delta region into the TN/OH valleys and extreme southern Appalachians. Surface high pressure remains centered over the southern/central Appalachians late today and continues to reinforce a dry llv airmass. The atmospher will moisten with time from the top down with likely to categorical PoP features west of I77 by 12z - spreading across the entire fcst area by midday Sunday. Temperatures will slowly warm into late morning across the entire fcst area leading to all rain by midday as highs top out in the upper 30s across the mtns to upper 40s over the Piedmont. Rainfall amounts through Sunday afternoon are fcst to be around 1-1.25 inches across the southwest/central NC mtns and northeast GA, tapering down to the east with a half to quarter inch favored at GSP and CLT respectively.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 215 PM EST Saturday: A split flow pattern early in the period evolves into a single flow Atlantic ridge and broad central and western CONUS trough by the end of the period. The northern wave of the split flow on pushes a frontal boundary across the area. The combination of deep moisture and synoptic scale lift, along with isentropic lift, will spread rain across the area through the night. Although surface temps across the Northern Mountains will be in the mid 30s overnight, a nearly 10 degree C low level warm nose will keep precip as all liquid. Lows will be around 5 degrees below normal. QPF values will range from tenth to a half an inch from north to south. The moisture and lift move east and south of the area early Monday as high pressure builds in from the north and sets up in a cold air damming pattern. As this takes place, the southern stream upper low over the Rio Grande opens up and moves across Texas. Short wave energy moves through the flow ahead of the low and across our area. The associated surface low moves east along the Gulf Coast spreading a moist southerly flow across the SE CONUS. Precip spreads back into the area from the SW in response. QPF will be light. Temps will be tricky with the damming high setting up, but precip tapering off across portions of the area. Expect highs generally in the low to mid 50s, but they could be higher where precip ends and lower where it lingers. Precip develops in earnest Monday night as the upper low tracks into MS and the surface low takes on a Miller B pattern. Deep moisture returns, along with strong synoptic and isentropic forcing. This will strengthen the damming high across the area. As the surface lows track east on Tuesday, the southern wedge boundary does lift north toward the area. However, expect it, and any resulting instability or thunderstorms, to remain to our south as well. Still, given the PW values and strength of the forcing, expect QPF values to range from around 0.75 inches near the TN border to 1.5 inches along the southern tier of the CWFA. Lows Monday night will be around 10 degrees above normal with all liquid precip. Highs will be near normal across the mountains where the damming influence is less, to around 5 degrees below normal elsewhere. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 245 PM EST Saturday: A surface boundary should be south of our county warning area (CWA) Tuesday evening as a deamplifying upper level trough and vort max quickly sweep northeast into Virginia. This will allow any lingering POPS to end quickly in the evening. Wednesday a rather non descript pattern as the atmosphere reloads to the west, and the surface pattern across our region remains "baggy" with a weak flow. Conditions should remain dry for the balance of the day. A strong H5 trough will rotate into the middle Ohio Valley Wednesday night and Thursday, signaling a change in our weather pattern. This will allow a shot of cold air to begin a plunge into the region. Thermal structure continues to show a downward trend in thickness and H85 temperatures from late Wednesday night through Thursday - at least. We will continue with low POPs from late Wednesday night into the wee hours Thursday night - with weak vorticity advection/cold air advection and a bit of moisture. Deepest moisture should be in our North Carolina mountains. Speaking of our North Carolina mountains it appears to be cold enough for a change to all snow showers, although precipitation amounts should be light at the moment. Cold high pressure will then build into the region Friday and Saturday. Temperatures around normal Wednesday will start a much colder trend in the Thursday through Saturday time range, perhaps some 10 to 15 degrees below normal. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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At KCLT and Elsewhere: Profiles continue to steadily moisten from the top down this evening but precipitation has been breaking out from the southwest a bit quicker than progged. Still anticipate VFR conditions through at least 06Z west to 08Z east with gradually improving light rain coverage. Conditions will deteriorate to steadier MVFR conditions from KAVL to the Upstate TAF sites, but take a few hours longer at KHKY and not reach KCLT until 15Z. Any onset precip at KAVL is expected to be liquid, but profiles remain interestingly cool in the higher terrain nearby. Lowering MVFR conditions through the day on Sunday will tend toward IFR during the afternoon along with steadier moderate rain. Expect winds to adjust back more solidly to ENE to NE east of the mountains as the rain spread in, but with SE flow at KAVL. Outlook: A brief lull is possible Monday with the best chance for heavier rain and widespread restrictions on Tuesday. Brief dry weather is expected on Wednesday, with another front approaching from the west. Confidence Table... 00-06Z 06-12Z 12-18Z 18-00Z KCLT High 100% High 100% High 89% High 86% KGSP High 100% High 89% Med 75% Med 76% KAVL High 100% High 83% High 84% High 96% KHKY High 100% High 93% High 90% High 91% KGMU High 100% High 90% Med 76% Med 77% KAND High 100% High 87% High 86% 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 and ensemble forecasts are available at the following link:
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&& .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...SBK NEAR TERM...CDG/HG SHORT TERM...RWH LONG TERM...TS AVIATION...CDG/HG is the U.S. government's official web portal to all federal, state and local government web resources and services.