624 FXUS62 KGSP 101854 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 254 PM EDT Wed Oct 10 2018 .SYNOPSIS... Heavy rain and gusty winds associated with Hurricane Michael will impact the area tonight and Thursday. Cool high pressure will build in Friday and bring seasonably cooler and drier air into the region through the weekend. A cold front will impact the area early next week with a chance of showers. && .NEAR TERM /THROUGH THURSDAY NIGHT/... Band of showers/embedded isolated thunderstorms is expected to continue to pivot gradually to the north, as narrow subsident/ mid-level drying region north through northeast of the outer bands of Hurricane Michael continues to overspread the forecast area. Thus, the lull in precip that is currently underway across the Upstate and northeast GA should be experienced this evening across western NC...except perhaps along the eastern Blue Ridge escarpment, where strong (albeit weakening) upslope flow will likely keep moderate to heavy rain going through the afternoon. Storm total amounts of 1.5-2.5 inches have already occurred in the upslope areas (mainly from Lake Lure north), and we're already seeing some advisory-level hydro issues in these areas, and conditions should only continue to gradually deteriorate through the afternoon/ evening. Some moderate instability has developed across the southern half of the forecast area, where breaks in the clouds have occurred. While shear will be increasing throughout the day, the stronger shear is not expected until late this evening through the overnight, and will thus lag the better instability by several hours. Therefore, there probably isn't much of a severe weather threat this afternoon, but we have already seen development of a couple of discrete thunderstorms south of the forecast area, and we'll probably see more of this going into the evening. The outer bands of Matthew will quickly overspread the forecast area from the southwest beginning around midnight-ish, with very heavy rainfall rates expected from the get-go. There will be a window from 06-ish to 15-ish Z in which ingredients will be sufficiently aligned to produce a tropical tornado concern south and east of I-85, although the higher threat will certainly be south of the forecast area, which will be more solidly in the right front quad/ favorable hodograph environment. In terms of the winds, being that Michael has made landfall as a category four storm, there is some concern that the traditional model guidance may be spinning the storm down too quickly, thus under-doing the inland winds. This is always a very tough forecast, and the Tropical Storm Warning that was issued earlier for our southern tier of zones was mainly done to accommodate the tropical storm wind probability info from NHC. The other wind-related concern is the potential for hybrid convective gusts associated with any intense rain bands, which could easily produce occasional 50 mph (or greater) winds. Thus, while our official forecast doesn't really support the headlines, the uncertainty regarding the intensity of the cyclone and the potential for occasional higher end wind gusts warrants continuation of the Tropical Storm Warning. Of course, the primary concern going forward will be the heavy rainfall, flood/flash flood potential. As the cyclone experiences increasing environmental shear on its northeast track, it will take on more in the way of extra-tropical characteristics, with the axis of heaviest rainfall becoming increasingly concentrated in a relatively narrow (i.e., ~75 mile) axis along and to the left of the cyclone center associated with intense deformation zone. Thus, the track of the storm will be critical in determining which areas just get heavy rain, and those that get intense/excessive rainfall. 3-5 inches, with locally higher amounts of as much as 7 inches will be possible within this axis. Being that the bulk of that would fall in < 10 hours, flash flooding is certainly a concern, with the most likely area of concern being across the lower/eastern SC Piedmont, and the southern NC Piedmont, including much of the Charlotte metro area. A secondary enhanced area of concern will be along the eastern Blue Ridge escarpment, where additional amounts of 2-4 inches appear likely, on top of the 1.5-2.5" that have already occurred. No changes are necessary to the Flash Flood Watch at this time. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 230 PM Wed: A pattern change will commence Thursday night as cooler high pressure begins to build into the region from the west. With a strong pressure gradient across the mountains, a few wind gusts are possible. Otherwise, the first cooler temperatures of the season will push into the region with lows Friday morning in the 40s in the mountains and 50s in the Piedmont. High pressure will push across the region Friday and Saturday with a comfortable fall feel to the pattern and no rainfall expected. Highs will be in the 60s in the mountain valleys and 70s in the Piedmont. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 230 PM Wednesday: A series of troughs will drop into the central part of the county during the early to middle part of next week. A surface cold front will bring the chance of showers to the mountains on Sunday and the entire forecast area on Monday. High pressure will build in for Tuesday and Wednesday leading to seasonably cool and dry conditions. Temperatures will be autumn-like with morning lows in the 30s and 40s in the mountains and 50s in the Piedmont. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... At KCLT and elsewhere: Showers will fairly widespread in the vicinity of the NC terminals for at least the next 2-3 hours, with thunderstorms becoming increasingly probably late this afternoon near KCLT, warranting a tempo for such there. Meanwhile, a lull in the convection has developed at the Upstate SC terminals (and should eventually develop at the NC terminals during the evening), but we may see isolated/widely scattered showers and thunderstorms develop within destabilizing air mass. Conditions will then go down hill overnight, as tropical storm Michael approaches from the southwest. Cigs will likely begin lowering to IFR/LIFR at most terminals by mid/late evening, generally continuing through Thu morning before improving during the afternoon. Heavy rain/gusty winds will overspread the area after midnight through tomorrow morning, with LLWS becoming likely at most terminals by daybreak. Winds are expected to gust in the 20-30 kts range, primarily from the E and NE, but occasional gusts in excess of 30 kts will be possible in association with heavy rain bands. Outlook: Expect quickly improving conditions Thu afternoon and evening, with gusty northwest winds continuing. Fair conditions develop for the weekend, but restrictions will be possible again early next week as a cold front approaches the area. Confidence Table... 19-01Z 01-07Z 07-13Z 13-18Z KCLT High 93% High 89% Med 79% High 93% KGSP High 95% Med 69% High 93% High 81% KAVL High 94% Med 74% Med 70% Med 72% KHKY High 96% Med 76% High 84% Med 72% KGMU High 87% High 81% High 94% Med 75% KAND Med 78% High 86% High 92% High 90% 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...Flash Flood Watch from midnight EDT tonight through Thursday evening for GAZ028-029. Tropical Storm Warning for GAZ029. NC...Flash Flood Watch through Thursday evening for NCZ033-049-050- 053-064-065-501>510. Flash Flood Watch from Thursday morning through Thursday evening for NCZ035>037-056-057-068>072-082. Tropical Storm Warning for NCZ082. SC...Flash Flood Watch from midnight EDT tonight through Thursday evening for SCZ002-003-005>007-010>013-019. Flash Flood Watch from Thursday morning through Thursday evening for SCZ008-009-014. Tropical Storm Warning for SCZ009-011>014-019. && $$ SYNOPSIS...SW NEAR TERM...JDL SHORT TERM...SW LONG TERM...SW AVIATION...JDL