Scientific Forecaster Discussion

000 fxus62 kgsp 222304 afdgsp Area forecast discussion National Weather Service Greenville-Spartanburg SC 704 PM EDT Mon Apr 22 2019 Synopsis... warm and dry high pressure will be in control of our weather until Thursday. Low pressure approaches from the west on Thursday and may linger into the weekend. && Near term /through Tuesday/... as of 700 PM EDT monday: only minor tweaks to hourly trends this evening, with no major changes to the forecast. Otherwise, with surface high pressure continuing to build in, quiet, Spring-like conditions have prevailed across the area today with nearly clear skies, light SW winds, and temperatures well into the low to mid 70s. Do expect temperatures to climb another degree or two before capping off for the day. Into tonight, expect nearly clear skies to continue with temperatures dropping into the lower 50s across the upstate and northwest Piedmont, cooler across the mountains - overall around normal. Trending from last night, do anticipate Mountain Valley fog to develop again late overnight through before daybreak. Any lingering fog will quickly dissipate after daybreak. On Tuesday, sfc high pressure with building ridge aloft will continue to allow for a dry weather pattern across the western Carolinas and northeast Georgia. Expect temperatures to climb well above normal, with lower 80s, with pockets of 70s across the mountains. && Short term /Tuesday night through Thursday/... as of 200 PM EDT monday: an upper ridge will continue to build over the southeast states on Wednesday, as a closed upper low tracks into Texas. Meanwhile, a northern stream trough will dig into the Great Lakes, and push a weak cold front into the Ohio Valley. Westerly flow ahead of that front, combined with rising heights aloft should bump temps about 8-10 deg above normal under mostly sunny skies. The latest guidance generally agrees that the front will push roughly thru the NC zones Wed ngt and stall out thru Thursday. The front will have little moisture to work with, but a few isolated showers may develop, esp along the Tennessee/NC border with help from westerly upslope. Lows will be about 10 deg above normal under increasing clouds. Thursday, the upper low will open up into a southern stream trough and approach the area from the west. The low-level flow will turn out of the SW and moisture will gradually increase mainly from the top-down. There will be an increase in pop across the west Thu aftn into Thu night, but the east will likely stay dry. Temps will continue to be about 8-10 deg above normal. && Long term /Thursday night through Monday/... as of 230 PM EDT monday: there is still some disagreement among the guidance on with the merging of the split stream troughs over the eastern states Thursday ngt thru Friday. The 12z GFS agrees fairly well with the ensembles and the 00z European model (ecmwf) on better phasing of the upper troughs and a cleaner fropa of the associated front. The front should cross the area early Fri morning thru Fri aftn. Based on that timing, most of the destabilization will occur from the I-85 corridor and east. Even then, SBCAPE looks to be only a few hundred j/kg. Shear does not look that impressive, and the way the front lays over the area from the northwest doesn't result in very strong frontal convergence. So the severe threat, while probably non-zero, should be low on Friday. Precip should move out to the southeast by early Friday evening, with gradual clearing. Temps will remain above normal. Dry high pressure briefly builds in Saturday under quasi-zonal flow aloft. Then a series of shallow impulses will ripple thru the flow with guidance quickly out of phase of timing associated weak fropas from Sunday thru the first half of next week. Overall, conditions should be dry (with some slight chcs possible, mainly in the mountains) with temps near to slightly above normal. && Aviation /23z Monday through Saturday/... at kclt and elsewhere: VFR through the period at the taf sites, though Mountain Valley fog may form again. Winds will remain out of the S to SW through the period for all but kavl (where northwest winds will prevail), generally under 5kt but picking up tomorrow as Lee troughing increases. Gradient won't be quite as noticeable at kclt where speeds should remain near or just slightly above 5kt, but other sites should inch up toward 10kt and some low-end gusts not out of the question. Outlook: aside from the potential for Mountain Valley fog in the morning, expect VFR conditions to prevail through mid week. Periods of showers and thunderstorms associated with a cold front will bring the potential for showers and thunderstorms towards the end of the week, with flight restrictions possible. Confidence table... 23-05z 05-11z 11-17z 17-18z kclt high 100% high 100% high 100% high 100% kgsp high 100% high 100% high 100% high 100% kavl high 100% high 100% 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: Www.Weather.Gov/gsp/aviation && Gsp watches/warnings/advisories... Georgia...none. NC...none. SC...none. && $$ Synopsis...deo

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