Area Forecast Discussion
Issued by NWS Greer, SC

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671 FXUS62 KGSP 201537 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1037 AM EST Sat Jan 20 2018 .SYNOPSIS... High pressure will move offshore this weekend and allow a warm southerly flow through Monday. A rainy cold front will cross the region Tuesday followed by dry high pressure persisting through the end of the work week. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 AM EST Saturday: Made a few tweaks to sky and temps as moisture along the TN line continues to yield widespread upslope stratus, while elsewhere temps are warming nicely. Therefore adjusted sky along the NC/TN border by increasing such along the ridges/peaks, and also bumped temps up a few degrees. Otherwise the prevailing fcst is in good shape. Will let the black ice SPS go on schedule at the top of the hour given temps in the upper 30s to lower 40s across the piedmont. Previous Discussion: A split flow pattern persists across the SE CONUS today/tonight while a weak srn stream h5 low traverses south of the FA. Upper heights will rise ahead of the low which will help keep the area dry along with above normal warmth by a couple cats. The NAM continues to be the only guidance indicating upslope precip across the far wrn NC mtns. Soundings across the spine indicate any precip that falls would be frozen in the form of fzdz or sleet this morning as a weak warm nose forms within a shallow moist layer. Have adj the going slt PoPs by limiting the potential to the nrn mtns. If any precip occurs it will transition to rain arnd 14z with no sigfnt accums thru the day. The raw model guidance and some MOS output is showing a distinct minima in max temps across the NC Piedmont today. This is confusing considering rising heights...persistent llvl theta/e adv and a downsloping h85 flow. So...went with the warmer ADJMAV and even bumped this up a degree or two with good insol on tap. With increasing llvl moisture...mins will remain abv freezing over most areas for the first time in a week. && .SHORT TERM /SUNDAY THROUGH TUESDAY/... As of 230 AM EST Saturday: Short wave ridging builds over the area Sunday and Sunday night ahead of a deep upper low moving into the central plains. At the surface, the center of high pressure moves across the area and offshore. Southwesterly flow and rising heights will lead to above normal temps both periods. After a foggy start and lingering clouds across the mountains skies clear during the day with returning clouds overnight. Heights fall through Monday night as the upper low moves into the lower Great Lakes and the associated trough south of the low moves into the southern Appalachians. Short wave energy rounds the low and moves across the area. However, the best energy moves by to our north. A strong upper jet moves toward the area as well but the best divergence also moves by to our north where the left exit region of the jet is located. At the surface, low level south to southwesterly flow strengthens Monday as a cold front moves into Middle TN. This brings increasing moisture into the area. With the best forcing remaining to our west during the day, precip will be slow to move in but will increase in the southerly upslope flow areas during the afternoon. The front moves into the area Monday evening then east of the area overnight. A strong southerly low level jet moves in with the front increasing wind speeds and moisture and creating strong shear. Helicity values will be quite high as well. The NAM has MUCAPE values up to around 300 J/kg while the GFS is much less. The SREF mean does show a good chance of over 100 J/kg MUCAPE values. This creates the potential for a high shear/low CAPE scenario Monday night as this system moves through. Heavy rain will be a possibility as well with copious moisture and strong southerly flow. Temps will be above normal. The front quickly moves east Tuesday taking the moisture and forcing with it. There will be some lingering moisture along the TN border in the developing NW flow during the morning, so cannot rule out some light snow showers. Highs will be near normal mountains and around 5 degrees above normal elsewhere. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... As of 315 AM EST Saturday: A weak clipper-type short wave moves across the east coast Wednesday and Wednesday night. Do not expect any precip with this system but an increase in clouds and continued windy conditions across the mountains is likely. Temps drop back to near normal for Wednesday and Thursday. Surface high pressure remains over the area Friday as an upper ridge builds overhead. This keeps precipitation to our west. Temps remain steady or rise slightly on Friday. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/... At KCLT and Elsewhere: No restrictions thru the TAF period all sites outside of some possible MVFR VSBY over the NC terminals arnd daybreak Sun. Otherwise...the atmos will remain very dry thru a deep layer as an area of upper forcing and moisture crosses south of area. A low-level ridge and sfc high pressure will maintain weak sfc winds aligned w/ly to sw/ly non/mtns and up-valley across the mtns today with decoupling expected aft midnight. Some increase in llvl clouds across the mtns this morning/afternoon while FEW/SCT Ci crosses from the southwest all sites. Outlook: Potential for MVFR Monday into Tuesday with an approaching cold front. Otherwise expect VFR. Confidence Table... 15-21Z 21-03Z 03-09Z 09-12Z KCLT High 100% High 100% High 100% High 100% KGSP High 100% High 100% High 100% High 100% KAVL High 100% High 100% High 96% High 96% KHKY High 100% High 100% High 100% High 94% 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: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...SBK NEAR TERM...CDG/SBK SHORT TERM...RWH LONG TERM...RWH AVIATION...SBK

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