Scientific Forecaster Discussion

000 fxus62 kgsp 180532 afdgsp Area forecast discussion National Weather Service Greenville-Spartanburg SC 132 am EDT Tue Jun 18 2019 Synopsis... seasonal temperatures and humid conditions will persist over the next few days while unsettled weather returns ahead of a front drifting down from the Great Lakes. Drier weather is expected at the end of the week, but it might be short lived. && Near term /through today/... 130 am update...made some adjs to pops and the wx grids based on the ongoing evolution of convective activity. Surface temps and TD/S are remaining a little abv the fcst curve and dropping slowly steady state as layered moisture remains quite high across most locales. Expect some NC mtn valley fg/stcu developing over the next few hrs...possibly across the non/mtns as well nearer daybreak. As of 1015 pm: deep convection blossomed along the leading edge of a deeper moisture plume, characterized by about 1.8" of precipitable water per the 00z kffc soundings. This activity is also focusing along the southern Escarpment, where short term guidance indicated strengthening low-level southerly flow in response to gradually tightening gradient, as well as along an outflow boundary emanating from convection across far northwest NC. While a pulse severe storm or two cannot be ruled out...especially in association with cell mergers, the main threat from this activity is expected to be localized flash flooding, especially along the southern/near the southern Escarpment, where training and anchoring of cells has been observed, and may well continue, resulting in potential hourly rainfall rates of up to 3 inches. Convection should gradually diminish in coverage and intensity overnight, but may never completely go away. As a mid-level synoptic wave currently over the Mississippi Valley continues to move eastward, thunderstorm chances will be greater on Tuesday. While wave weakens quite a bit over the next 24 hours, there is plenty of moisture available and limited capping, so that increasingly widespread thunder showers will be likely on Tuesday as main positive vorticity advection of the wave crosses over the region. Wind shear remains weak, with convective instability moderate, giving some chance for severe weather, primarily in the form of short-lived severe winds from storm outflows. Precip totals today and tomorrow are highly variable from place-to-place, depending on which areas directly receive thunderstorms. Areal averages run around a quarter inch today and a half inch tomorrow over the mountains, with lower amounts elsewhere. Low-level features change little over the next 36 hours as broad high out in the Atlantic edges slowly eastward, with light southwesterly surface winds that will keep humidity elevated and temperatures a little above normal, with little change in day-to-day temperatures. && Short term /tonight through Thursday night/... as of 150 PM EDT monday: the short-term forecast picks up at 00z on Wednesday with a weakening upper shortwave moving over the fcst area from the west. What's left of the feature will move off the coast by late Wed. On thurs, another upper shortwave will amplify to our west and begin to move over the County warning forecast area as the period ends late Thursday. At the sfc, warm and moist southerly flow will be in place as the period begins. A weak cold front will move thru the fcst area on Wednesday and move offshore by Wed evening. The profiles behind the front are marginally drier, but the change is modest at best. With a lingering Lee trof over the area on Wednesday, sfc winds may become more westerly behind the front briefly, but they will revert back to a more southwesterly direction by Wed evening. On thurs, a substantially stronger and deeper low will develop south of the Great Lakes and lift NE towards New England. This low will bring a more robust cold front to our doorstep early thurs and move it through the County warning forecast area late thurs. In its wake, cooler and drier high pressure will spread over the region to end the period. As for severe potential, the Thursday fropa appears to be more of a threat. It's expected to move thru the area during the peak heating window or just after it. In addition, there will likely be more low to mid-lvl shear/helicity with this front and drier air aloft. Thus, we will need to keep a close eye on the fcst going forward. Temps will remain a few degrees above normal. && Long term /Friday through Monday/... as of 120 PM EDT monday: starting at 12z Friday with the strong shortwave moving out over the Atlantic and a ridge building in from the Mississippi Valley. Friday will be a dry day for almost everybody under weak high pressure. The dry weather lasts at least a few hours longer in the European model (ecmwf) into Saturday. A series of small, mesoscale convective systems (mcs) are shown on the GFS model to affect at least the mountains over the next several days. The ec is more oriented to shortwave movement and the Saturday through Monday night period is shown to be a buildup in activity leading to the arrival of the shortwave Tuesday mainly over Kentucky and Tennessee. If the activity is mcss, those would be forming over the plains states then move towards US as they weaken. The highest cape values will remain to the west of our region but 1500 to 2500 cape is forecast each afternoon and early evening from the mountains to the upper Savannah River valley. Temperatures slightly above normal with Sunday being the warmest day. && Aviation /06z Tuesday through Saturday/... at kclt and elsewhere: the taf period will see continued vicinity tstms across the NC zones thru 10z or so. With plenty of llvl residual moisture and most sites receiving precip...expect low ceilings and visibility into the MVFR/IFR range developing before daybreak and persisting thru mid-morning. Another convectively active afternoon is in store with a frontal zone crossing thru mid day. The better thunder chances will be at kavl as the bndry pushes into the NC mtns early...while prob30 thunderstorms and rain will time the best ts chances as the line moves east later this afternoon and evening. Expect more ceiling/visibility flight restrictions aft 00z thru the overnight across all taf sites. Outlook: continued afternoon convection with possible flight restrictions, mainly across the higher terrain, along with increasing chances for morning valley fog/low stratus are expected thru the week. Confidence table... 05-11z 11-17z 17-23z 23-00z kclt high 100% high 100% high 100% high 100% kgsp high 100% high 100% high 100% high 100% kavl high 100% high 91% 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. && $$

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