Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 291852 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 252 PM EDT Wed Mar 29 2017 .SYNOPSIS... Dry high pressure will build into the area from the north through tonight. Moisture will gradually increase through the day tomorrow, with abundant moisture in place by Friday as a strong low pressure system moves east from the Mississippi River Valley. Drier weather will return for the weekend, with unsettled weather returning early next week. && .NEAR TERM /THROUGH THURSDAY/... As of 250 PM EDT: Enjoy the rest of the afternoon and evening because change is on the way. The upper ridge axis over the area tonight slides east to the coast Thursday. High pressure remains ridged into the area from the NE tonight into Thursday. Low level moisture increases over the area tonight with deep layer moisture increasing on Thursday as upper heights begin to fall and flow becomes SW ahead of an upper low moving into the Mid-South. The low level flow becomes steadily more upslope in nature tonight and increases in magnitude Thursday. Isentropic lift increases through time as well. All this leads to increasing clouds tonight and a chance of rain and drizzle developing along the Blue Ridge after midnight. This precip spreads out across the CWFA through the day Thursday as deep moisture moves in and stronger forcing develops. With the surface ridge nosed in from the NE and clouds and precip developing, a cold air damming wedge develops. The guidance differs a little on where the southern extent of the wedge and resultant TMB. The NAM, ECMWF, and SREF all showing instability developing over NE GA, much of the Upstate, and the NC Mountains indicating a farther north boundary than the GFS. The GFS shows little to no instability keeping the boundary farther south. Have gone with a blend to come up with thunder chances Thursday afternoon. This keeps TSRA limited to west of the French Broad valley in NC, and generally west of I-26 across the Upstate and into NE GA, though only small chances at best for northern Greenville and Spartanburg Counties. Lows tonight will be quite mild 10 to 15 degrees above normal. Highs Thursday will show the wedge pattern, with near normal readings along and south of the I-85 corridor and the TN border counties. Highs will be below normal along the Blue Ridge into the NC Foothills and NW Piedmont. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... As of 2pm EDT Wednesday: First of a series of strong dynamical spring systems reaches the area Thursday night/Friday morning with a round of showers and thunderstorms. Current expectations are for very marginal instability with CAPE below 500 j/kg and LI of -1, combined with deep layer shear to 55 kts. Showers and some thunder are a good bet Thursday night/Friday morning, but severe potential will depend on some improvement in parameters over what is now forecast. As the system moves eastward on Friday, diurnal warming will increase instability, with improved chances for SVR as the system exits out of eastern parts of the CWA. Region should receive useful amounts of rainfall with this first system Thursday night and Friday morning with storm total rain amounts of around a half inch to an inch, with locally heavier amounts with the deeper convective cells. Wedge/CAD regime in place on Thursday brings some low-level moisture from the southeast into the area with some upslope showers in the higher terrain. Somewhat cooler air and CAD-related cloudiness will limit the development of surface-based CAPE. CAD will be disrupted by wet passage of major frontal system Friday morning, with low-level winds veering to westerly and eventually northwesterly behind the front. Frontal passage will be accompanied by gusty winds, especially at higher elevations with 850mb winds of 30 to 40 kts. Passage of front will scour moisture and create drying conditions for the balance of Friday and clearing by Saturday morning; with fair weather on Saturday. Temperatures on Friday will warm some over Thursday pre-frontal, with post-frontal temperatures recovering rapidly on Saturday in clear skies. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 215 PM EDT Wednesday: the extended fcst picks up at 00z on Sunday with upper ridging building back over the region as a very deep upper trof digs down over the SW CONUS. The upper trof will approach the fcst area on Monday and move across the CWFA early Tuesday. The system is expected to lift NE of the area by early Wednesday with flat upper ridging spreading back over the region in its wake. At the sfc, Canadian high pressure will be pushing into the fcst area from the north early Sunday but is expected to drift NE of the region later in the day. At the same time, a vigorous low will develop over the ArkLaTex region and lift NE on Monday and move a warm front over the Carolinas. The system is expected to lift north of the fcst area on Tuesday and push a cold front thru the CWFA as it does. Things should dry out late Tuesday/early Wednesday as the low moves NE of the region. As for the sensible fcst, Sunday should be dry with POPs ramping up quickly from SW to NE Monday morning. Chances for widespread showers and thunderstorms, some of which could be strong to severe, remain high Monday afternoon thru early Tuesday with lingering showers possible for the remainder of Tuesday. I kept a slight chance POP over the NW half of the CWFA on Wed for any lingering showers. Temps will remain above normal, for early April, thru the period. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... At KCLT and elsewhere, surface high pressure will continue to build down across the forecast area from the north today and persist through tonight. Winds have toggled SE or ESE outside of the mountains and SSE at KAVL. These winds will continue until this evening when they toggle back to NE. They remain light SSE at KAVL. Stronger ENE winds outside of the mountains and S wind at KAVL expected Thursday morning. Low VFR clouds become BKN this evening then lower to MVFR then IFR before daybreak as moisture increases and upslope flow develops. Cigs lift back to low MVFR at KCLT but remain IFR elsewhere with MVFR vsby developing as isentropic lift and cold air damming wedge develops bringing rain and drizzle across all but KCLT. Outlook: Showers and thunderstorms develop over the SC sites and possibly KAVL Thursday afternoon as the wedge weakens and instability develops. The approach of a strong storm system will bring continued chances of restrictions as well as a potential for heavy rain showers and thunderstorms Thursday night and Friday. Drier conditions will return again for the weekend. Confidence Table... 19-01Z 01-07Z 07-13Z 13-18Z KCLT High 100% High 97% Med 76% High 100% KGSP High 100% High 100% Med 71% High 96% KAVL High 100% High 100% Med 64% High 95% KHKY High 100% High 94% Med 71% High 84% KGMU High 100% High 100% Med 73% High 93% KAND High 100% High 100% Med 71% High 81% 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: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...Wimberley NEAR TERM...RWH SHORT TERM...WJM LONG TERM...JPT AVIATION...RWH

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