661 FXUS62 KGSP 210009 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 809 PM EDT Mon Aug 20 2018 .SYNOPSIS... A warm and humid air mass will remain in place across the region tonight as a cold front approaches from the west. The cold front is forecast to move across the region on Tuesday afternoon and evening with scattered to numerous thunderstorms expected. In the front's wake, drier high pressure will spread over the area for the latter half of the week. && .NEAR TERM /THROUGH TUESDAY/... As of 5pm EDT Monday: Blended in CAM data to reduce POP in the southwest quadrant of the CWA as CAM guidance and radar/satellite trends have much less coverage in that area this evening. Showers with some thunderstorms will continue until after dark with further initiation expected over the mountains and some southeast movement into the foothills and piedmont areas. Patchy areas of fog will be possible towards daybreak. With high temperatures ranging from the low to mid 80s this afternoon, expect temperatures tonight to drop into the low 70s, cooler across the mountains. Back to the west, a closed upper low pushing eastward from the Plains will gradually open up as it moves into the OH Valley overnight, as it's north to south oriented associated cold front slowly pushes through the MS Valley. Per latest guidance, anticipate the front to near the western portion of the FA towards the end of the near term forecast period. Thus, with the front to the west, persistent SW flow, and upper support from a few passing waves of energy, expect another round of scattered to numerous showers and thunderstorms on Tuesday. While more impressive shear values along with other severe weather parameters will remain well to the north, will note the potential for isolated severe thunderstorms, as noted in the Marginal Risk from the SPC Day 2 Convective Outlook. Primary threat will be damaging winds. High temperatures on Tuesday will be around, if not just a few degrees above, normal. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 205 PM EDT Monday: A sharp upper trough axis moves east of the area to be replaced by a more broad and weaker trough for Wednesday and Thursday. At the surface, a cold front moves east of the area Wednesday, but a weak lee trough remains over the area. Low level flow turns northwesterly behind the departing front with deep moisture moving east as well. There will be some lingering low level moisture, so scattered diurnal convection may develop across the mountains, with isolated convection possible near the lee trough. High pressure builds in from the northwest for Thursday. This turns the low level flow more northerly or northeasterly. The atmosphere looks to be too stable for any diurnal convection to develop. Highs will be near normal Wednesday then fall to nearly 5 degrees below normal on Thursday as the cooler air mass associated with the building high pressure moves in. Lows follow a similar pattern. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 200 PM EDT Monday: Surface high pressure will build down into the forecast area on Friday leading to a cooler than normal day. Dewpoints are expected in the 50s to lower 60s which will feel very comfortable for this time of year. The high will slowly move off the coast over the weekend with a gradual modification to more normal conditions. Mid level ridging is expected to develop for the early part of next week with hot and muggy conditions returning. Some scattered storms are expected early next week primarily in the mountains. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Showers and some thunder will linger for a couple more hours this evening, primarily over the mountains, with very sparse activity after 02Z. Areas which saw significant rainfall today will be the ones most like to see restrictions due to fog Tuesday morning, particular the KAVL, KGSP, and KGMU aerodromes. On Tuesday, a major front will approach the region from the northwest, with the frontal position reaching KAVL by 0Z Tuesday evening. Winds will remain southwesterly ahead of the front at 5 to 15 kts, and will veer more northerly after 00Z when the front passes. Front will help to focus showers and thunderstorms on Tuesday, with significant activity expected along and ahead of the front. Timing in TAFs for VCTS and PROB30 TS reflect expected progress of the front, with storms once again beginning over the mountains and spreading southeastward. Outlook: Expect good coverage of diurnal showers and thunderstorms thru early Wednesday. After which, drier high pressure is expected to build in behind a passing cold front. Until then, restrictions are likely mainly during the morning as low clouds form, and then under any afternoon and evening showers and thunderstorms. Confidence Table... 00-06Z 06-12Z 12-18Z 18-00Z KCLT High 100% High 82% High 82% High 100% KGSP High 91% Low 55% Med 73% High 100% KAVL Low 57% Low 37% Med 71% High 100% KHKY Med 71% Low 36% Med 66% High 94% KGMU High 88% Low 58% Med 71% High 82% KAND High 92% Low 55% Med 74% Med 67% 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...SW NEAR TERM...SGL/WJM SHORT TERM...RWH LONG TERM...SW AVIATION...WJM