Area Forecast Discussion
Issued by NWS Greer, SC

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406 FXUS62 KGSP 101953 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 253 PM EST Sat Dec 10 2016 .SYNOPSIS... Cold high pressure overhead tonight will move off the mid Atlantic coast Sunday as another cold front crosses the Plains states. Expect this front to cross our region Monday with rain chances remaining into mid week. Another blast of cold air will settle across our area in the later half of the week. && .NEAR TERM /THROUGH SUNDAY/... As of 215 PM EST: The upper level flow pattern will become increasingly zonal tonight into Sunday. Meanwhile, cold and dry surface high pressure centered over the Appalachians will move off the east coast through Sunday. With any appreciable mid level moisture moving by to the north, overnight clouds should be confined to thin cirrus and another cold night of mins in the 20s throughout is expected. Broad upper troughing will then develop through Sunday over the central CONUS. Meanwhile, 850 mb flow will toggle southerly overnight and increase through Sunday, with low level Atlantic upglide moisture steadily making a run into the region from the southeast. Anticipate mainly an increase in clouds, but with isolated light rain PoPs developing in south/southeast upslope areas as well as across the lower piedmont late in the day. Onset profiles are marginally cold/dry enough for a light rain/snow mix along the higher ridges with any early arriving precip, but this will not be featured since PoPs are so low. In addition, ridge top winds will become gusty in the improving southerly flow through Sunday afternoon. Temps will rebound marginally, but the rise will be limited by increasing clouds despite the improving southerly flow. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... At 2 PM Saturday: on Sunday night nearly zonal upper level flow will be in place over the CONUS. This pattern persists into Tuesday, with the bulk of upper level energy channeled across the northern tier of states. The GFS does show and advection vort lobe crossing the Southern Appalachians on Monday morning however. At the surface, on Sunday night moisture will be increasing across Northeast Georgia and the Western Carolinas in advance of an approaching cold front. The front reaches the Southern Appalachians by Monday morning, moving to the Piedmont by afternoon. The front stalls to the south of our area on Monday night, while moisture persists to its north across our area. This pattern persists into Tuesday. Precipitation over our area is expected to start as early as late Sunday in the mountains, and spreading east across the rest of the area Sunday night. The main issue with this forecast will be precipitation type on each night. With a warm nose aloft present, snow is not expected. Some guidance suggests freezing rain in isolated portions of the mountains, while other guidance is warmer to begin with and would support liquid rain. Temperatures will generally run above normal. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 245 PM EST Saturday: The medium range fcst period kicks off on Tuesday night amidst broad cyclonic flow aloft, while a cold frontal axis slowly shifts south through north GA into the Carolinas. Behind this front is a rather broad cold/dry continental high pressure system that should be promoting modest/improving caa across western NC at fcst initialization. As such, moist northwest H85 flow looks to lift mechanically along the western slopes of the southern Apps thereby yielding a brief round of nwfs Wednesday morning, while further south thermal fields look to warm to yield any wintry ptypes, thus all liquid is favored. This all rain ptype will remain persistent into Wednesday evening before Canadian high pressure dives through the Plains into the OH/TN valleys ushering a reinforcing cold front across the southern/central Apps Wednesday night into Thursday. Developing H85 northwesterly flow will once again promote upsloping during this time frame, with latest accums across the NC high terrain at generally 1-1.5 inches of less. This cold ridge of high pressure will slide east through the remainder of the week, setting up as classical or hybrid CAD event (Depending on which model source is favored). Nevertheless, both the ECMWF/GFS favor some degree of a developing Miller B pattern as a Plains low ejects northeast into the OH valley, spreading moisture northward atop the entrenched CAD Friday night, while an Atl coastal low develops by Saturday afternoon/evening. Profiles during this Miller B setup will initially favor wintry precip Friday evening/night into Saturday morning before warm advection yields a ptype phase change to all liquid by midday Saturday. It should be noted that confidence in ptypes is rather low at this range therefore only a rain/snow mix was featured in the fcst, however profiles do suggest that fzra/ip could also be in the mix. Temperatures through the period will start out near/above normal, falling below normal into Thursday and thru Friday behind the reinforcing front, before finally warming back to near normal amidst the late fcst period warm advection. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... At KCLT and elsewhere: VFR conditions will continue through the period as surface high pressure moves from the Appalachians to the Atlantic coastal waters. High, thin clouds will increase through the period, but low level Atlantic upglide moisture will begin to invade from the southeast toward the end of the period. Will keep any late Sunday morning cloud bases at VFR levels, but MVFR will be increasingly possible just beyond the TAF period. Winds will be light throughout and mainly southerly early in the period. Some adjustment back toward easterly is expected across the foothills, but southeasterly should be a good average through 18Z. Outlook: Moisture will increase ahead of an approaching cold front Sunday night through Monday with mainly a cold rain and associated restrictions expected. Conditions remain unsettled through mid week as the passing front stalls just to the south of the area and moisture returns. Confidence Table... 20-02Z 02-08Z 08-14Z 14-18Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 100% High 100% High 100% High 100% KHKY High 100% High 100% High 100% High 100% KGMU High 100% High 100% High 100% High 100% KAND High 100% High 100% 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 and ensemble forecasts are available at the following link: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...HG SHORT TERM...JAT LONG TERM...CDG AVIATION...HG is the U.S. government's official web portal to all federal, state and local government web resources and services.