Area Forecast Discussion
Issued by NWS Greer, SC
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031FXUS62 KGSP 171032AFDGSPArea Forecast DiscussionNational Weather Service Greenville-Spartanburg SC632 AM EDT Sat Aug 17 2024.SYNOPSIS...A cold front will approach the area today and push east throughtomorrow, bringing scattered showers and thunderstorms bothafternoons. Drier conditions will return next week with low rainchances and below normal temperatures through at least Thursday.&&.NEAR TERM /THROUGH TONIGHT/...-- Changed Discussion --
As of 620 am: Spotty convection continues across the CWA...barelywarranting a 20 PoP this morning. Otherwise, areas of fog/lowstratus will continue across the area until late morning, primarilyin locations that received significant rainfall Fri evening. Somelocally dense fog remains possible, esp in mountain valleys.Heights will fall across the region throughout the period, as anupper low wobbles southeast across the Great Lakes region, and aseries of short wave troughs pass south of the low center across theOhio Valley and vicinity. A lee/pre-frontal surface trough isforecast to take shape across the forecast area today, and alongwith typical terrain/differential heating effects will provide theprimary source of lift for diurnal convective development thisafternoon into the evening. PoPs primarily in the 20-40% range areadvertised for much of the area, with the highest chances focusednear the Blue Ridge. Strong insolation and dewpoints of around 70will support robust destabilization, with sbCAPE of around 2500 J/kglikely by late afternoon. Taller updrafts will be capable ofproducing severe weather, primarily in the form of damagingdownbursts. However, accelerating mid-level flow will support deeplayer shear values of around 30 kts...so some updrafts could exhibitmodest mid-level rotation and perhaps pose an additional threat ofmarginally large hail.Convective coverage and intensity will likely peak during earlyevening. However, additional activity originating from a frontalzone to our west could wander into western areas well into theovernight...warranting maintenance of chance PoPs near the TN/NCborder through the night. Temps are expected to be a couple ofdegrees above climo through the period.-- End Changed Discussion --
&&.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...As of 152 AM EDT Saturday: The latter half of the weekend remainsa question mark as a cold front slides east of the forecast areathrough Sunday evening beneath the a deep z500 trough extendingsouth from Quebec. Guidance still indicates that while the greaterconvective threat on Sunday will be to the east of the forecastarea, there`ll still be some initiation beneath a lobe of deep DPVArounding the base of the trough...likely over the I-77 corridor,where operational models depict surface-based instability to thetune of 1500 J/kg by late afternoon overlapping some 25-30kts of0-6km shear within a 500mb speed max. Although there remains somevariability in the ensembles, the overall spread of the convectiveparameter phase space is tightened significantly compared tolast night, so confidence is improving that SPC`s Marginal Riskfor Severe Weather over the eastern zones will be realized.Otherwise, high temperatures Sunday will be within a category ofnormal everywhere except the Upper Savannah River Valley, where thelack of convective coverage paired with low-level WAA early in theday will support temperatures as much as a category above normal.Sunday night and Monday, more pronounced drying will resultfrom the cold front`s passage east, and even without accountingfor afternoon mixing, dewpoints will be 5-8 degrees lower Mondayafternoon compared to the previous afternoon. In the NW flow regimewhich develops Monday, breezy conditions can be expected. Only themountains can expect some isolated to scattered ridgetop convection;other zones will be weakly forced or even slightly suppressed bythe postfrontal air...and so should remain dry through the day.Temperatures will be a category or so cooler across the area onMonday, only climbing into the mid 80s in most locations.&&.LONG TERM /TUESDAY THROUGH FRIDAY/...As of 215 AM EDT Saturday: Continental high pressure will meanderacross the Ohio Valley through at least the first half of theworkweek, maintaining dry conditions on Tuesday, Wednesday, andThursday. Some ensemble solutions bring at least diurnal ridgetopconvection back into the forecast by Thursday afternoon, but othershold off until Friday or beyond. Operational guidance is in prettygood agreement that NE low-level flow will be maintained throughthe end of the period...which should maintain less-than-favorableconditions for convection through the end of the period.Still expect well-below-normal temperatures through the week.&&.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...-- Changed Discussion --
At KCLT and elsewhere: Isolated convection is ongoing across theTerminal Forecast Area this morning. Other than a VCSH here andthere, chances for a direct hit on a TAF site are too low to includea mention at this time. Otherwise, VLIFR cigs will continue at KHKYand KAVL through 13 or 14Z. Can`t rule out a brief restriction atone of the other sites, but it`s looking increasingly unlikely atthis point. SW winds will increase to 6-8 kts by afternoon, withscattered diurnal convection expected to develop by late afternoon.Prob30s for TSRA are warranted at all sites beginning at 21Z, withVCTS or VCSH warranted at KAVL/KHKY/KGSP/KGMU beginning duringmid-afternoon. While convection is expected to decrease in coverageand intensity this evening...similar to this morning, isolated-to-widely scattered convection will remain possible through theovernight.Outlook: A cold front will track over the forecast area Sunday withconvection expected possibly into Monday. Drier conditions returnbehind the front by Tuesday. Patchy fog and low stratus will bepossible each morning in the mountain valleys and in any locationsthat received heavy rainfall the day prior.-- End Changed Discussion --
&&.GSP WATCHES/WARNINGS/ADVISORIES...GA...None.NC...None.SC...None.&&$$SYNOPSIS...MPRNEAR TERM...JDLSHORT TERM...MPRLONG TERM...MPRAVIATION...JDL
