Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 010718 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 218 AM EST Mon Mar 1 2021 .SYNOPSIS... A cold front will cross the mountains early this morning and then cross the foothills and Piedmont through the late morning and early afternoon hours. Dry high pressure will build over from the north tonight into Tuesday. Unsettled weather returns from the west Tuesday night into Wednesday morning. Another low pressure system may affect the Gulf Coast region Friday into Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 215 am EST: The latest surface analysis reveals a cold front just west of the spine of the southern Appalachians early this morning and beginning to make steadier forward progress. Ahead of this boundary, gusty southwest winds have developed over the higher terrain, but with max gusts likely staying just below advisory values of 45 mph along the highest ridge tops. Precipitation will begin to fill in quickly across the NC mountains as the frontal zone and associated H5 vorticity reach the spine of the southern Appalachians through the early morning hours, march on to the Blue Ridge Mountains eastern escarpment by daybreak, then move east across the foothills/Piedmont through late morning. The PoP trends will follow this pattern, with categorical coverage likely at some point for most locations, but with QPF values much better along the TN border areas early this morning, and particularly across Graham and Swain Counties in the best upslope flow and longest dwelling period of the heavy rainfall. With QPF values around 1.5+ inches in these areas, minor hydro problems could arise, but this should not be sufficient for any widespread flooding and a Flash Flood Watch does not appear to be needed. Instability remains quite marginal in profiles. Will generally keep thunder out of the forecast, but an isolated rumble cannot be completely ruled out with the fropa. Temperature trends will be hard to pin down today, with falling temps likely in the cold advection across the mountains, steady temperatures across the northern tier in balanced cold advection but warming post-fropa downslope flow, and a modest afternoon bump in temps in the western Upstate and NE GA. Gusty northwest winds will also develop in the cold advection through the day, but with gust values again below advisory criteria in the windiest mountain locations where a secondary, reinforcing cold fropa arrives this afternooon. A trailing but vigorous shortwave will reach the mountains again by late day. However, the deeper moisture should settle generally southeast of our Piedmont counties by sundown along with the passing cold front. Any shallow upslope moisture into the western mountains will dry up fairly quickly in the cold air along the spine of the mountains this evening. So, any isolated snow showers or flurries will be short-lived and non-accumulating. 1032 mb surface high pressure will then build over the OH River valley tonight, with chilly thicknesses spilling southward east of the Appalachians. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 145 AM EST Monday...A split flow pattern aloft will evolve into a general trof over the period as a srn stream h5 low traverses the FA Tue night into Wed. A broad offshore sfc low will be supported by this upper energy and will bring a decent amt of GOM/Atl moisture to the area beginning Tue afternoon. Meanwhile, a cP sfc high will track off the midAtl coast and provide a weak insitu ridge before breaking down Wed morning. This general pattern will likely support a wintry mix of precip across the NC mtns Tue night, with light snow transitioning to freezing rain, then to rain by 15z Wed. The latest NAM soundings dropped across the NC escarpment show a strong and deep warm nose interacting with sub-freezing sfc temps abv 3.5 Kft to support -fzra, while the GFS is notably warmer with llvl partial thicknesses and indicates more of a sn/ip situation. So, have blended the llvl thermal profiles and used a top down approach for p/types, which generated arnd an inch of snow across the higher peaks with perhaps up to 2 inches over the Smokies. The freezing rain would begin arnd 08z and persist into mid morning with a few hundredths of an inch favoring the nrn BR escarpment. If these ice amts hold over the next few fcst cycles, an advisory may be issued. The atmos dries out during the day Wed as a Canadian high drops south and reinforces a srn stream sfc high building in from the west thru the period. Max temps will remain a little below normal each day, while mins hover arnd or a bit abv normal levels. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 210 AM EST Monday...The ext range fcst looks to remain quite dry as the models continue to show a suppressed large-scale pattern over the SE CONUS. Thus, little change was made to the already dry fcst. A stg subs zone will slowly cross the area, while a couple cP sfc highs build south and force a favored storm track well south of the FA each day. With winds generally maintained n/ly and weak CAA flow in place beginning Thu night, expect max temps to begin the period Thu abv normal, then cool a little below normal Fri thru Sun. Dewpoints will drop and mix out each afternoon, which could create some fire-wx concerns across NE GA based on RH each afternoon, except Sun when llvl moisture begins to return to the area. Winds shud remain relatively weak, however, and plenty of sunshine will be had making for rather nice days for early March. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... At KCLT and elsewhere: Anticipate mainly thickening and lowering VFR ceilings early this morning as a cold front and associated deeper moisture moves in from the west. The narrow band of frontal moisture should provide some MVFR to lower end VFR cigs during the passsage of the main bands of rain showers with the front, generally from just before daybreak west to mid-morning east. Returning VFR cigs will then lift and scatter through the afternoon hours, with just SCT high clouds tonight as drier high pressure builds in from the north. Gusty southwest flow this morning will become slightly gustier W to NW flow this afternoon following fropa and the onset of cold advection. Most locations lose the gusts by early evening, but KAVL will be the exception with continued NW gusts into the 20s through 06Z Tuesday. Outlook: VFR conditions briefly persist into Tuesday under dry high pressure. However, moisture may surge back into the area by Tuesday night, with restrictions and precipitation chances returning through early Wednesday. Another round of drying is expected by late Wednesday, likely continuing through the end of the work week. Confidence Table... 07-13Z 13-19Z 19-01Z 01-06Z KCLT High 100% High 95% High 100% High 100% KGSP High 95% High 91% High 100% High 100% KAVL High 83% High 99% High 99% High 100% KHKY High 99% High 100% High 100% High 100% KGMU High 95% High 95% High 100% High 100% KAND High 96% High 97% 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 are available at the following link: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...HG NEAR TERM...HG SHORT TERM...SBK LONG TERM...SBK AVIATION...HG

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