Area forecast discussion National Weather Service Greenville-Spartanburg SC 1055 am EDT sun may 19 2013 Synopsis... a weak upper level trough will linger over the region through Monday...then will move off to the east. The forecast area will remain in a moist and rather unstable airmass...before a cold front crosses moves through late in the week. && Near term /through tonight/... as of 1040 am...large complex of showers that developed along a speed convergence axis associated with west/SW low level jet continues to dissipate over our southern zones late this morning. Meanwhile...the focus for heavy rainfall in the near term has shifted well west of the gsp County warning forecast area...across northwest/ctrl Georgia...at the leading edge of the more robust instability. The afternoon convective picture for our County warning forecast area is nominally clearer than it was yesterday. With only a few patchy areas of showers around this morning...fairly rapid clearing of the overcast is occurring...especially across the NC mountains this should allow for moderate levels of instability to develop this afternoon...allowing for greater coverage of showers and storms that was seen Saturday afternoon. It is somewhat difficult to pinpoint any particular areas for higher probability of precipitation...but short term models do indicate an area of low level convergence/confluence setting up over the eastern zones this afternoon...and we will focus 80 probability of precipitation across this area. Once again...an isolated severe storm cannot be ruled out...but heavy/locally excessive rainfall will continue to be the primary threat. Current indications are the most likely area for heavy rainfall will be across the eastern zones... where low level confluence could aid and abet training of cells... and slightly enhanced low level shear could also promote some degree of mesoscale organization. However...considering the uncertainty in this evolution...as well as the fact that ffg/S are very high in those areas...Don/T think I can justify issuance of a watch in this or any other area during the afternoon. As of 655 am...large area of convection over the sav River Valley will slide southeast through the morning. Additional convection moves into the mountains during the morning as rain showers slowly increase through the morning elsewhere. Expect widespread rain showers by afternoon with increasing chance of thunderstorms and rain. Still expecting some areas of heavy rain through the morning. Short wave rotating through the open wave of an upper low crosses the area today. A southerly low level jet moves across at least the southern portion of the County warning forecast area as well. These features will combine with the moist unstable air mass already in place to produce widespread showers and thunderstorms. Storms with heavy rainfall on the nose of the low level jet are moving toward the are across Georgia. However... there is a definite southeasterly trajectory to the storms with the heaviest rainfall. That said...storms with heavy rainfall could develop almost anywhere over the County warning forecast area. This presents no easy way to handle any watch issuance. Trying to pick one area over another may lead to less concern over another area where flooding could develop. Issuing for the entire County warning forecast area will certainly be too broad. Therefore...will just continue the mention in the severe weather potential statement. May still see an isolated severe storm this afternoon given moderate deep instability and some shear with the jet. Expect convection to diminish overnight as the forcing moves east of the area. However...the flood and severe threat will into the evening. Lows will be 5 to 10 degrees above normal. && Short term /Monday through Tuesday night/... at 300 am EST Sunday...on Monday the upper trough axis will move slowly over the Interstate 77 corridor. The GFS brings this weakening upper feature east of our area on Monday night as an upper ridge arrives...while the NAM leaves it almost stationary. On Tuesday the GFS ridge axis reaches The Spine of the Appalachians. On Monday as the upper trough axis moves east...drier air aloft will move in from the east...instability and shear increase...supporting more of a convective Mode...even as coverage gradually decreases. Shear will decrease on Monday night. Tuesday features less shear... but even greater instability...and more dry Ari aloft and beneath the cloud layer...supporting evaporative cooling and downdraft production. Instability is slow to wane on Tuesday night. Temperatures will trend upward from Monday to Tuesday...reaching above normal values...as heights rise aloft. && Long term /Wednesday through Saturday/... at 300 am EST Sunday...an upper ridge axis will cross the eastern Seaboard on Wednesday...while and upper trough crosses the MS River Valley. The trough crosses the Ohio and Tennessee valleys on Thursday...and crosses the central and southern Appalachians on Friday. On Saturday the European model (ecmwf) moves its trough axis slowly off the coast...while the GFS trough axis remains along the East Coast. The Carolinas and Georgia remain in a warm and moist air mass on Wednesday and Thursday. Both the European model (ecmwf) and GFS show Atlantic moisture moving into the southern Appalachians in an easterly upslope component Wednesday...and moisture associated with a former cold front converging with the Atlantic moisture on Wednesday night. The models also show a weak surface low moving up the Florida Peninsula...feeding more Atlantic moisture into the Georgia and Carolina coasts. The models differ on whether the remains of the old front will sweep east of our area on Thursday. The European model (ecmwf) supports does so... moving moisture out of our area...while the GFS keeps moisture over our area until the surface low moves off to the NE on Friday. A cold front will approach from the northwest on Thursday night...crossing our area on Friday. Saturday will feature cool and dry high pressure building in from the north. Temperatures will cool from slightly above normal on Wednesday to around normal later in the week as heights fall aloft. && Aviation /15z Sunday through Thursday/... at kclt and elsewhere...a weak upper wave will cross the region. Widespread rain showers with isolated thunderstorms and rain near the western sites will move east to the eastern sites by late morning or early afternoon. Ceilings and visibility are already low and will slowly increase through the day to VFR. Restrictions will be limited to convection during the afternoon and evening. However...IFR ceilings will return after midnight. S to SW winds will continue through the period. Outlook...showers and thunderstorms...and associated restrictions... will persist through Monday. Fair weather may return by Tuesday. Confidence table... 15-21z 21-03z 03-09z 09-15z kclt high 100% high 95% high 93% high 96% kgsp high 90% high 91% high 82% medium 75% kavl high 91% high 96% medium 74% medium 75% khky high 91% high 95% high 91% medium 78% kgmu high 93% high 93% high 83% medium 75% kand high 95% high 96% medium 78% medium 75% 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...jat near term...jdl/rwh short term...jat long term...jat aviation...rwh