Area Forecast Discussion
Issued by NWS Greer, SC

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000 FXUS62 KGSP 260033 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 833 PM EDT Tue Jul 25 2017 .SYNOPSIS... High pressure moving by to the north is expected to provide cooler temperatures on Wednesday. Another front will move in from the northwest late in the week, with cooler and drier conditions arriving behind it for the weekend. && .NEAR TERM /THROUGH WEDNESDAY/... As of 8pm EDT Tuesday: A few remnants of convection are all that remain over the area which will continue to decline as we end a relatively quiet evening. The pattern of events on Wednesday may be fairly similar to today, with some widely scattered afternoon showers, but low chances for anything very strong. Not much change in the synoptic setup over the last 12 hours as an H5 trof ejects over the northeast CONUS, and a large anticyclone dominates westward across the plains. At the surface, a quasistationary frontal axis remains draped in the vicinity of the I85 corridor. Temperatures on Wednesday will be a bit cooler than today thanks to the aforementioned mid/late morning stratus potential, yet should still top out within 1-2 degrees of normal across the piedmont/fthills, and at normal levels across the higher terrain. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... As of 200 PM EDT Tuesday: Upper-level heights will begin falling from the Great Lakes to the Ohio River Valley Wednesday night through Thursday. At low levels, Light southerly upslope flow could permit isolated to scattered showers, with a thunderstorm or two, to persist into the nightttime hours early Thursday across the southern mountains. Otherwise, anticipate slightly better diurnal convective coverage across the NC mountains Thursday afternoon and evening ahead of the approaching upper support as surface-based instability increases a bit over previous days. Improving westerly steering flow will also likely bring scattered convection farther east of the Blue Ridge along the I-40 corrdor into the western NC foothills/piedmont into Thursday evening. Surface to 6 km bulk shear magnitude may rise to 25 to 30 kt across the northern tier by Thursday afternoon as these westerlies improve. Thus, anticipate a gradual change in the character of the convection to more multi-cell types by late Thursday. The upstream shortwave energy will cross the forecast area from the northwest Thursday night through Friday ahead of much stronger heights falls carving out a more prominent trough from the Great Lakes to the Appalachians. The best moisture and forcing will occur around the passing cold front, but the numerical models still exhibit quite a bit of spread on the timing. The faster NAM/ECM camps bring clouds and moisture into the region very early Friday and thus limit instability, while the GFS timing is much later in the day. Indeed, the slower GFS would keep precipitation going well into Friday night across the southeast half of the area. This will play havoc will instability around the fropa and also shear profiles, but an uptick in storm organization is certainly possible Friday afternoon and evening. For now, will blend the timing slightly toward the faster solutions which is preferred given the push from the rapidly falling upstream heights. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 200 PM EDT Tuesday: A trend toward drier and cooler conditions seen in the previous forecast was continued with this forecast package. By Saturday morning, a surface cold front should have moved through our area and settled to our south. The GFS/ECMWF remain in agreement on maintaining an amplified pattern and sweeping this front through towards the Gulf coast, with an upper longwave trough deepening over the eastern CONUS over the weekend and into early next week. There is also better agreement in the global models with respect to drier air arriving behind the front...and with basically all convection remaining suppressed Saturday and Sunday over our area in yet another guidance cycle, have lowered pops even more to below climo over the weekend. The Bermuda high reasserts itself a bit more over the southeast early next week, and gradual moistening of the column will lead to pops returning closer to average by Tuesday and Wednesday. With the above-mentioned upper trough expected to deepen dramatically over the eastern CONUS over the weekend and into early next week, maintained the downward trend in temperatures through the period. Large adjustments weren`t made with this package, but temperatures more than 5 degrees below climo and dew points in the mid to low 60s could make for some...dare I say it...rather pleasant conditions for late July. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... At KCLT and elsewhere: Relatively stable weather pattern will continue through Wednesday with some widely scattered afternoon convective showers and light to variable winds. Some patchy fog and possible low OVC in the morning could affect some sites, especial KAVL. Probability of getting convection at any give site is low enough to not be worth mention in the TAFS at this time. Some fog and stratus overnight are possible as boundary layer cools. How much is difficult to be precise about, but will be less likely at KCLT and KGSP which have slightly lower forecast relative humidity levels. Outlook: Scattered diurnal convection can be expected each day thru Friday across the region. Then drier air will filter in from the north behind a passing cold front this weekend. Chances for morning fog and stratus will also be possible each day in the mountain valleys. Confidence Table... 00-06Z 06-12Z 12-18Z 18-00Z KCLT High 100% High 98% High 80% High 95% KGSP High 100% High 99% High 88% High 100% KAVL High 97% Med 64% Med 79% High 100% KHKY High 100% High 81% High 89% High 85% KGMU High 100% High 100% High 96% High 100% KAND High 100% High 89% High 94% 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: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...Carroll NEAR TERM...CDG/WJM SHORT TERM...HG LONG TERM...Carroll AVIATION...WJM is the U.S. government's official web portal to all federal, state and local government web resources and services.