Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 231102 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 702 AM EDT Sun Apr 23 2017 .SYNOPSIS... Cool and moist high pressure will remain over the area through Monday. Meanwhile, a deep and vigorous low pressure system moves across Georgia to the Carolina coast creating a lengthy period of moderate to heavy rainfall that persists through Monday. Dry high pressure returns by Wednesday. Temperatures warm through next weekend with a small chance of afternoon mountain thunderstorms. && .NEAR TERM /THROUGH TONIGHT/...
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As of 700 AM EDT: Showers are blossoming across the CWFA, as isentropic lift and moisture deepens atop a strengthening wedge. No significant changes were needed with this update. As of 330 AM EDT: an upper closed low will continue to slowly drift SE from the Mid-South to near Columbus, GA by 12z Monday. This slow drift will place the CWFA within a region of very strong deep-layer Q-vector convergence, especially tonight. At the surface, an area of low pressure will stall over northern GA, while a backdoor cold front clears our area to the south keeping a hybrid wedge locked in across the entire CWFA. Persistent low level upglide atop the wedge should bring rounds of showers thru the day. The CAMs seem to agree on perhaps a couple "rounds" of categorical PoPs, one this morning, then another this evening. Total QPF amounts today thru tonight will range from generally 1.5 to 3", highest across the SELY upslope areas of the Blue Ridge and adjacent foothills. So the Flood Watch looks good for the NC zones. As for severe potential, it really does look like the wedge front will make little progress north as the low is slow to approach from the west, and ongoing rain keeps it reinforced. I keep a mention of slight CHC to CHC for thunder across the I-85 corridor and south/east, due to potential elevated convection. There is still a marginal risk in the Day One Convective Outlook for possible hail and wind, but the CAMs keep the strongest convection south and east of the CWFA. Temps will be nearly steady across most of the area, unless the wedge front does nudge back into the southern tier of counties, where temps may bump back up into the upper 60s to lower 70s. Lows tonight drop slightly into the 40s in the mountains and lower to mid 50s elsewhere.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 355 AM Sunday: The heavy rain potential continues Monday as our area will still be in the southerly diffluent flow/deformation zone around the upper low moving east from west central GA to the SC/GA coast. Upper divergence follows a similar pattern. Strong low level easterly flow remains over the area as the low level low pressure areas follow a similar pattern as well. In fact, the low level easterly flow is up to 3 standard deviations above normal. This will create strong isentropic lift over the cold dome from the damming that remains in place. The moist air mass remains in place as well with PW values 1 to 2 SD above normal. The heaviest rain will likely fall across the NC Foothills and Piedmont, but could shift south into the Eastern Upstate. An additional 1 to 2 inches of rain could fall in these areas. Therefore, have added Union County NC to the Flood Watch to cover the potential. Moderate to heavy rain could linger Monday evening, but precip tapers off from SW to NE overnight. Highs will increase a little but remain around 10 degrees below normal. Lows will be up to 5 degrees above normal. Precip continues tapering off from SW to NE Tuesday ending during the afternoon. With precip ending and sunshine gradually returning, highs will be near normal. Dry forecast continues Tuesday night with lows around 5 degrees above normal. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 330 AM Sunday: Short wave ridge over the area Wednesday moves east as a series of short waves move by to our north and west Thursday and Friday. A stronger ridge develops over the SE CONUS Saturday. Dry remains over the area Wednesday with temps above normal. Moisture returns ahead of a weak cold front Thursday and Friday. This will lead to diurnal convection each day favoring the mountains. Temps remain above normal. Southerly flow around the ridge surface and aloft will keep some moisture across the mountains with diurnal convection once again. Temps remain above normal as well. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/...
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At KCLT and Elsewhere: As expected, IFR cigs have finally filled in across all the TAF sites (except barely MVFR at KAVL), as showers continue to develop atop a building cold air damming wedge. Guidance is still on track for a period of heavier rain/greater coverage this morning, then perhaps a relative lull this afternoon. Then another round of rain tonight. Still may see some elevated thunder across the upstate and at KCLT late this afternoon thru the evening. For now, only will mention a PROB30 at KCLT where chance is greatest for embedded thunder with the second round of rain. IFR cigs will likely lower to LIFR across the piedmont sites tonight, as the cold dome of the wedge starts to shrink with a passing area of low pressure to the south. Showers will start to taper off in the west toward the end of the TAF period. Outlook: An area of low pressure will cross the southern CWFA thru Monday while strong sfc ridging builds in from the north. Widespread low clouds and precipitation are expected to persist thru this time. Conditions should gradually improve Tuesday thru Wednesday morning as dry air works in behind the departing low. Confidence Table... 11-17Z 17-23Z 23-05Z 05-06Z KCLT High 100% Low 50% Med 78% Med 60% KGSP High 87% Low 50% Med 78% High 87% KAVL High 87% Med 78% Med 78% High 87% KHKY High 81% High 83% High 83% Med 69% KGMU High 81% Low 44% Med 78% High 87% KAND High 87% Med 61% High 100% High 87% 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...Flood Watch through Monday evening for NCZ033-035>037-048>053- 056>059-062>065-068>072-082-501>510. SC...None. && $$ SYNOPSIS...RWH NEAR TERM...ARK SHORT TERM...RWH LONG TERM...RWH AVIATION...ARK is the U.S. government's official web portal to all federal, state and local government web resources and services.