Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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767 FXUS62 KGSP 041733 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 133 PM EDT Tue Jun 4 2024 .SYNOPSIS... Scattered showers and thunderstorms are on tap with afternoon storms persisting into Thursday. Dry air will mix in Friday and persist into the weekend with a small chance of mainly mountain thunderstorms returning for Sunday afternoon. && .NEAR TERM /THROUGH TONIGHT/... As of 1002 AM EDT Tuesday: No major changes to the forecast this morning. What`s left of a weak band of showers is rapidly losing steam over the eastern SC Upstate, and will continue to do so over the coming hour or so. Patchy fog has largely scattered out, although intermittent low-vis obs are still being reported along the Savannah River Valley and some of the NC mountain valleys. With time, the upstream shortwave trough will lift into the Tennessee Valley by tonight. 850mb flow will also increase to 15- 25kts as a low-level jet over the Southern Plains also translates east. This will in turn advect a deep moisture plume from Georgia into the western Carolinas with PWATs surging to near 2". The 00z suite of CAMs is in good agreement that scattered to numerous showers and thunderstorms will be possible this afternoon within this very moist and moderately buoyant airmass. Afternoon insolation will support modest instability of 1500-2500 J/kg, although CAPE profiles in forecast soundings will remain tall/skinny. Lapse rates will also be poor with limited downdraft CAPE, which will ultimately hamper severe weather potential. However, as with any summer convection, a couple strong to isolated severe thunderstorms will be possible with wet microbursts being the main hazard. The greatest chance for an isolated severe storm will be with any clusters and/or loosely organized line segments that can organize along composite cold pools. Deep moisture profiles will also support efficient rainfall rates, but ~20kts of flow within the cloud layer should promote enough storm motion to limit a threat for flash flooding. Locally heavy rates could still result in ponding/minor flooding of flood prone areas, however. As has been the case the last several nights, scattered showers and an isolated thunderstorm or two will likely linger well past the diurnal maximum through the overnight hours. Coverage may be greater tonight given continued moisture flux/flow and the approach of the upper trough from the west. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 200 AM Tuesday...The atmos remains active thru the short range period. A full latitude trof will be working across the MS Valley early Wed, which will maintain well defined upper difl flow over the fcst area. Meanwhile, waves of vort energy will traverse the flow and begin to break down an upper ridge during the afternoon. This will combine with a destabilizing atmos to produce rounds of convec, some of which could form multicell outflow cells in a weakly sheared environment. With sbCAPE reaching arnd 1200 J/kg, strong updrafts will be capable of producing large hail and severe criteria outflows. Things become more dynamic on Thu as a supported cold front approaches and crosses east which looks to occur during max heating. Shear levels increase and soundings show a tilted longer-lived storm potential as the prefrontal environment becomes more unstable than Wed due to warmer sfc levels. Thus, expect more of a severe threat with isol supercells maintained along and ahead of a passing sfc convg zone. With increasing dCAPE, the threat of damaging downbursts will increase, however, low level helicity looks to decrease after sunrise. So an isolated tornado threat will be non-zero, but not great either. Highs Wed will reach right arnd normal levels. Warmer BL air Thu due to increased llvl WAA will allow for highs pushing near 90 F outside the mtns and the m80s across the mtn valleys. Above normal lows are expected Wed night and near normal levels Thu night behind the frontal zone. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 220 AM Tuesday...Upper heights begin to drop Fri as a large and strong h5 low is blocked and deepens across the Glakes region. The guidance is still in sigfnt disagreement with the evolution of this low thru the latter ext range. The GFS is the most dynamic and swings an active occluded frontal low into the FA Sun afternoon into Mon, while the other op models are more progressive with the upper flow and maintain a much drier pattern. Thus will keep PoPs at low-end chance during that timeframe for now with precip possibly maintained non-diurnally each night as well. Otherwise and beforehand, deep nw/ly flow will produce a dry column Fri and Sat with near normal temps, lower sfc dewpts, and less humidity each afternoon. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... At KCLT and elsewhere: A complex aviation forecast sets up for this afternoon and tonight as multiple rounds of convection hit the area. Already, scattered cells are popping up over the NC mountains near KAVL and surrounding sites. Most hi-res guidance agrees that scattered to numerous shower and thunderstorm coverage will expand across the entire terminal forecast area. Some guidance suggests a well-defined line will lift up out of Georgia late this evening...such that at least for the Upstate terminals, convection will last well past sundown. Overnight, areas which received ample rainfall can expect MVFR to IFR vis restrictions...as well as widespread IFR ceilings. More recent runs of the HRRR now support some additional predawn showers, mainly across the Upstate terminals and KAVL. Diurnal convection is expected once again on Wednesday, possibly a little delayed compared to today. Outlook: Coverage of diurnal convection is expected to increase Wednesday evening as a frontal boundary moves into the region. Morning low clouds and fog will also be possible Thursday morning. Drier air will filter into the area Thursday afternoon and Friday morning, reducing chances for convection and restrictions, with relatively dry conditions continuing into the weekend. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...SBK NEAR TERM...MPR/TW SHORT TERM...SBK LONG TERM...SBK AVIATION...MPR