Scientific Forecaster Discussion

Area forecast discussion National Weather Service Greenville-Spartanburg SC 159 am EDT sun Oct 4 2015 Synopsis... an upper level low will drift slowly across the southeast United States through the rest of the weekend. Tropical moisture will produce widespread heavy to torrential rainfall across the region through Sunday night. Dry high pressure will build in beginning Tuesday. && Near term /through Monday/... as of 145 am EDT...a deep tropical moisture feed continues from the central SC coast through the midlands to The Heart of the upstate early this morning. The channeled warm conveyor belt from the tropical feed will become increasingly oriented west to east across the southern tier of the forecast area today as strong upper level divergence and middle level frontogenesis pivot over the southern tier. These forcing features are stemming from the 500 mb closed low center over SW Georgia early this morning...which is expected to move across North Florida the Florida coast tonight...and then NE over the coastal waters on Monday. As the low moves east...the deep layer q vector forcing north of the middle level circulation will lift back east across the midlands and coastal plain...but the ongoing moisture feed will be very slow to clear the forecast area. The easterly 850 mb jet will remain 40 to 50 knots through tonight before turning more nearly and weakening on Monday. The current flash Flood Advisory and npw hazards will remain in place for the moment. However...diminishing rainfall rates across the far northern tier will likely require some adjustment to the existing Flash Flood Watch through the early morning hours. && Short term /Monday through Tuesday/... at 230 PM EDT Saturday...on Monday morning a strong closed upper low will be off the Georgia coast...while and upper ridge will be over the plains...and another closed low will be over S California. By Tuesday morning the upper low moves NE along the Gulf a position off the southern NC coast...while features upstream slowly progress and deamplify slightly. On Tuesday night the eastern low fills...the ridge upstream reaches the eastern plains...and the western upper low reaches Arizona. At the surface...Sunday evening features diminished isentropic upglide...even though robust...moist...easterly upslope flow into the NC Blue Ridge will be present. As winds back from east to NE on Monday as the upper low moves up the Gulf Stream...upslope flow largely terminates...while moisture becomes confined mainly to the coastal plain. This drying trend over the Carolinas and Georgia continues through Tuesday...although the models show some lingering moisture over the southern Appalachians. Temperatures will run below normal in cool NE flow. && Long term /Tuesday night through Saturday/... at 230 PM EDT Saturday...on Wednesday morning a low amplitude upper trough will be along the East Coast...a low amplitude upper ridge will be over the plains...and a closed upper low will be over Arizona. By Thursday upper low becomes zonal over the NE USA...with very low amplitude riding over the southeast...while the upper low upstream reaches nm. By Friday model solutions diverge...with the European model (ecmwf) closed low retrogressing into northwest Mexico...and an upper trough amplifying over the Appalachians...while the GFS low reaches Texas...with ridging persisting downstream over the southeast. Little progression in these patterns occurs by Saturday morning. At the surface...on Wednesday morning high pressure will extend from the great leaks to the Gulf states and eastern Seaboard. As the high center progresses to Quebec on Thursday...the ridge becomes wedged up against the east slopes of the Appalachians. Southerly moist isentropic upglide over this ridge will be initially be over Florida and the Gulf Coast...but will spread north over our area by Friday... continuing into Saturday...while a slow moving cold front stalls and weakens to our west. Temperatures will run near normal. && Aviation /06z Sunday through Thursday/... at kclt and elsewhere...widespread rain will continue through the early morning hours...but with the heavy rain axis shifting southward from kgsp to kand through the day...and some gradual drying expected across the NC taf sites through the late period. Gusty NE winds around 25 knots will continue...except steady nearly flow at kavl. Expect mainly MVFR to IFR ceilings throughout. Will continue the low level wind shear mention at kavl...but low level wind shear appears more marginal at the foothill and Piedmont sites where low level east to NE flow is deeper despite the strength. Outlook...the moist easterly flow will diminish through the week... bringing drying and an end to rain and restrictions. Confidence table... 06-12z 12-18z 18-24z 00-06z kclt medium 77% medium 75% high 100% high 100% kgsp medium 71% high 82% high 87% high 100% kavl medium 74% high 81% high 95% high 100% khky medium 73% medium 75% high 90% high 95% kgmu medium 66% high 85% high 87% high 83% kand medium 67% high 81% high 94% high 98% 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 && Hydrology... have already seen widespread 2-4 inches across the area...with additional totals of 1-5 inches expected through the near term. These amounts take into account the guidance mentioned above and the south and west shifting axis of heaviest precipitation. As mentioned in the early morning discussion...the wet antecedent conditions will contribute to life threatening and damaging flashing flooding and river flooding as the heavier rain bands move across the region... particularly in the western upstate and NE Georgia later tonight where the bands may become stationary or pivot. The potential for numerous slope failures and debris flows will increase sharply once an additional period of heavy rain moves in over the southern Appalachians tonight. && Gsp watches/warnings/advisories... Georgia...Flash Flood Watch through Monday morning for gaz010-017-018- 026-028-029. Wind Advisory until 8 am EDT Monday for gaz010-017-018-026-028- 029. NC...Flash Flood Watch through Monday morning for ncz033-035>037- 048>053-056>059-062>065-068>072-082-501>510. Wind Advisory until 8 am EDT Monday for ncz033-035>037-048>053- 056>059-062>065-068>072-082-501>510. SC...Flash Flood Watch through Monday morning for scz001>014-019. Wind Advisory until 8 am EDT Monday for scz001>014-019. && $$ Synopsis...Ned near term...hg short term...jat long term...jat aviation...hg hydrology...rwh

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