Area forecast discussion National Weather Service Greenville-Spartanburg SC 150 am EDT Friday may 24 2013 Synopsis... an upper level trough will swing through the region tomorrow... bringing cooler and drier conditions for the weekend. Temperatures will moderate by the beginning of next week... with a chance of afternoon showers and thunderstorms each day concentrated over the mountains. && Near term /through today/... as of 1020 PM...current radar analysis places a line of convection extending in a north/south orientation across the southern North Carolina Piedmont...to include Charlotte metropolitan. This convection will continue to move eastward across central North Carolina before eventually dissipating due to lack of surface energy. Thus...slightly pulled back probability of precipitation further across the Piedmont to end slight chance probability of precipitation a little sooner than previous forecast. Winds still look to be somewhat gusty during the day tomorrow across the entire region as surface pressure gradient tightens. Thus for Friday expecting sustained north-northwest winds nearing 15-20kts across the higher terrain...and 12-15kts elsewhere. Look for gusts in the mountains to reach 25-30kts and around 15-20kts in the lower elevations. Therefore not forecast to reach Wind Advisory criteria at this time. Forecast looks to be on track and no changes were made. Remainder of previous discussion... The convection will be shunted east by the veering flow ahead of the main cold front...which is expected to cross the forecast area this evening as a short wave rounds the bottom of the upper trough and swings it eastward...carrying most of the clouds and showers with it. Expect some lingering shower chance on the Tennessee border through Friday morning with moisture being forced upward by the increasing northwest flow. On Friday...it looks like a breezy day with a decent pressure gradient as high pressure builds in from the northwest. An even more dynamic short wave will round the base of the trough and carry the trough axis farther east during the day...but this wave has no moisture to work with this far south. Mixing will be relatively shallow because of a strong inversion...which will prevent the tapping of the much stronger winds around 850 mb. Thus we should avoid any Wind Advisory issues. High temperatures will be a few categories cooler than today. && Short term /tonight through Sunday/... as of 210 PM Thursday...a strong upper low will move up the East Coast Friday night as an upper ridge builds over the central part of the country. This will allow a cool northwest flow to continue across the southern Appalachians through the weekend. At the surface...a ridge of high pressure with Canadian origin is forecast to extend from the Great Lakes southward to Florida Friday night. The high will control the weather through Saturday producing generally clear and seasonally cool weather. In fact...some sheltered mountain valleys could see some some scattered frost Friday night particularly in the little Tennessee Valley. On Sunday...an upper impulse in the northwest flow aloft will cross the area along with a weak backdoor surface front. Low level moisture will be lacking...but model time heights show middle and upper level moisture increasing which means an increase in cloud cover for Sat night into Sunday. Model quantitative precipitation forecast response is quite minimal on Sunday and anything that does fall would probably be just a few sprinkles over the mountains. Used a model blend for temperatures which advertises well below average temperatures for the entire weekend. Min temperatures Friday night will fall into the upper 30s over many mountain locations with 40s common elsewhere. Maximum temperatures will be in the 70s...except middle 60s to around 70 mountain valleys. && Long term /Sunday night through Thursday/... as of 145 PM Thursday...the 06z/12z GFS and 00z European model (ecmwf) are now somewhat at odds in regard to the upper level flow pattern. The main difference is that the GFS is quicker moving the anomolously strong upper low through New England and out of the picture. This allows the flow to deamplify over the southeast by Monday with an upper ridge building over the region by midweek. The ecm on the other hand keeps the southeast U.S. In a northwest flow regime to the east of an upper high it holds stationary over the lower Mississippi Valley. This allows weak impulses to translate across the region in the northwest flow making for a rather unsettled period until late week when the ecm finally builds the ridge to the east. The latest GFS ensemble supports the GFS operational runs. Wpc has favored the ecm in its medium range. However...I have hedged the forecast toward a blend of our gsp official/GFS/ecm which would put a diurnal harmonic to the forecast favoring scattered afternoon convection mainly over the mountains. The exception is Monday afternoon when some scattered showers/thunderstorms may also occur over the NC foothills/Piedmont as the backdoor front that slipped through the area on sun returns north as a warm front. Temperatures will begin the period a little below climatology...then warm to about a category above climatology by the end of the week. If the GFS solution verifies...maximum temperatures would be about a category higher each day. && Aviation /06z Friday through Tuesday/... at kclt...VFR with some lingering middle clouds for the first few hours of the 06z taf. A north-northwest wind expected through the period...increasing into the 10-15 knots range by middle morning...with gusts in the 20-25 knots range expected through the afternoon. Winds diminish around sunset this evening. At kavl...strong gap winds expected to pick up before daybreak...and continue through the day. Generally sustained 15-20 kts and gusts possibly in the 30-35 knots range. Some moisture will continue to work up the valley through about middle morning...with any ceilings expected to be VFR. However...a brief period of MVFR ceiling cannot be ruled out...most likely right before or during daybreak. Winds will begin to diminish after sunset this evening. Elsewhere...VFR conditions are expected at all other taf sites through the period...with middle clouds eventually clearing out by daybreak. Winds will be the main concern today. Expecting all sites to have winds in the 10-12kt range with gust approaching 25kts from late morning through the afternoon. Outlook...VFR through the period. Confidence table... 06-12z 12-18z 18-24z 00-06z kclt high 100% high 100% high 100% high 100% kgsp high 100% high 100% high 100% high 100% kavl high 84% high 97% high 100% high 100% khky high 100% high 100% high 100% high 100% 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: (must be lower case) Www.Weather.Gov/gsp/aviation_tables && Gsp watches/warnings/advisories... Georgia...none. NC...none. SC...none. && $$ Synopsis...level near term...cdg/PM short term...lg long term...lg aviation...Arkansas