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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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608 FXUS62 KGSP 161430 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1030 AM EDT Fri Aug 16 2024 .SYNOPSIS... High pressure will drift off the coast today, before a cold front will arrive over the weekend, bringing widespread showers and thunderstorms. Drier conditions will return next week alongside seasonable temperatures through at least Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1025 AM EDT Friday: Low stratus and fog have dissipated with some MVFR to VFR stratocu crossing the area. Convection, all but a lone shower moving into the NW Piedmont, has been much slower to start than previously expected. Expect good heating as the stratocu scatters out and cumulus develops keeping most areas mostly sunny for the bulk of the day. A short wave ridge will move east of the forecast area by the end of the day, with large scale height falls expected to impact much of the area along and west of the Appalachians by the end of the period. Within this pattern, increasing cyclonic flow aloft will provide for a more favorable scenario for convective development. Indeed, the bulk of short term guidance depicts scattered/numerous convective cells moving into and/or developing over the mountains this afternoon, and likely PoPs appear to be a good bet across much of this area. Things become a little more complex east of the mountains, as guidance generally agrees that instability will diminish from NW->SE across the foothills and Piedmont. The latest CAMs show scattered convection moving out of the mountains and across the NC Foothills and Piedmont late afternoon into the evening, but little over the Upstate or NE GA. Have kept the rather sharp PoP gradient will be advertise in the official forecast, such that chances are only 10-20% across out southern tier of counties. There will be a small risk of severe storms over the mountains, especially if any loosely organized convection is able to make a run for the CWA from the TN Valley. Max temps should be a little warmer than in previous days...placing them pretty close to...maybe slightly above normal. Convective coverage and intensity will diminish this evening, with very little in the way of coverage anticipated after ~mid-evening. However, with flow aloft becoming increasingly NW, can`t rule out some activity wandering into the NC mountains late tonight, and token small PoPs are carried there to account for that. Min temps are expected to be a degree or two above normal. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 148 AM EDT Friday: A robust longwave trough will deepen over the Eastern Seaboard over the weekend, producing multiple lobes of z500 vort energy through the period. By Saturday afternoon, a prefrontal trough will develop over the western Carolinas ahead of a strong cold front advancing across the Ohio Valley. Within this air mass, operational guidance depicts a tongue of 1200-2000 J/kg sbCAPE and some 30kts of 0-6km shear. Shear vectors will be oriented more or less perpendicular to the boundary...and a weak dry layer aloft will support marginal DCAPE values of 800-1000 J/kg...both of which support a severe threat over heavy rainfall threat despite PWs exceeding 1.75". Still, some localized heavy rain issues could present if storms train over the same areas. Temperatures should climb to no more than a category above normal Saturday afternoon. On Sunday, the 00z suite of deterministic guidance is beginning to align on a solution in which the frontal boundary has not yet made a complete passage across the region...and therefore can provide a point for convective initiation, at least across the eastern zones. These areas are now forecast to attain diurnal instability max in excess of 1000 J/kg, once again with non-trivial deep layer shear. No run-to-run consistency yet, and the broader envelope of ensemble guidance still depicts scenarios where the severe risk doesn`t pan out, but the dominant signal is now for a possible outside severe threat. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 205 AM EDT Friday: Long-range ensembles remain in decent agreement that the large scale pattern will only slowly shift next week, with upper troughing staying strong through Tuesday and then slowly deteriorating through the end of D7. Monday will feature a round of diurnal convection as postfrontal air manages to destabilize over much of the forecast area...although it`s unclear how much synoptic forcing will be available, so coverage remains in question. As NW flow drives ever-drier air into the region on Tuesday and beyond, and weak low-level CAA upsets already-waning lapse rates, we can expect drier conditions from Tuesday onward. Temperatures will be near or slightly below normal through the end of D7. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: Convection is expected to form (or move into) the NC mountains and foothills during the afternoon...with a tempo for TSRA warranted at KAVL, and a Prob30 for such at KHKY. Instability is forecast to weaken toward the Piedmont, so confidence wanes in terms of convection reaching the rest of the terminals, but there`s enough of a signal to add a Prob30 for SHRA at the upstate SC sites and at KCLT. Light/variable or calm winds will become SW at 5-7 kts late this morning/early this afternoon, generally continuing through the period. Outlook: A cold front will track over the forecast area this weekend keeping convection around. Drier conditions return behind the front early next week. Patchy fog and low stratus will be possible each morning in the mountain valleys and in any locations that received heavy rainfall the day prior. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...JDL/RWH SHORT TERM...MPR LONG TERM...MPR AVIATION...JDL/RWH