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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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502 FXUS62 KGSP 131338 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 938 AM EDT Tue Aug 13 2024 .SYNOPSIS... Dry high pressure gradually builds in from the north through Thursday, pushing a stalled front further south of the area. The high will drift east off the East Coast Friday, as a cold front approaches from the west over the weekend. The front will bring a return of better chances of shower and thunderstorms. && .NEAR TERM /THROUGH TONIGHT/... Key Messages... 1) Numerous Showers east of the Blue Ridge with Isolated Thunderstorms Possible this morning 2) Isolated Strong to Severe Storms Possible this Afternoon and Early Evening, mainly east of the mountains 3) Cooler Temperatures Expected Today As of 930 AM EDT Tuesday: Updated the precip probs over the Piedmont based on the ongoing numerous showers and embedded thunderstorms, mainly to raise into the likely range. So far, the activity has been relatively benign, but some of the precip rates have been on the order of 2 in/hr in the stuff that moved over Greenville, which resulted in some quick response on a few of the creeks. Fortunately, the convection is plodding along just fast enough to keep amounts in check. The precipitable water is relatively high, so the main concern will be duration, if the cell orientation leads to training over any particular area. Once this activity finally pushes off to the east, the CAMs are showing some redevelopment during the afternoon. That`s the stuff that could be a problem in terms of stronger storms. Otherwise, upper troughing will remain over the Carolinas through the near term while periodic shortwaves track over the region from the northwest. Meanwhile at the sfc, the southern periphery of surface high pressure centered over the Great Lakes region will extend into the Carolinas while a front stalls over the Southeast. This will lead to a more convectively active day compared to yesterday. Although deep layer shear will range from 35-45 kts, lapse rates look relatively poor and the sfc-based CAPE might make it to around 1500 J/kg during peak heating. The SPC Day 1 update kept the Marginal Risk over the eastern Piedmont of SC (south of CLT) today. Damaging wind gusts will be the main concern with any severe storms that develop. The excessive rainfall threat will remain isolated with higher shear values in place allowing for faster storm motion. However, flash flood guidance continues to be on the low side (mainly across the eastern two-thirds of the CWA) due to the rainfall from Debby last week and the recent rainfall over the weekend. Convection should gradually end from west to east this evening, with drier conditions moving in tonight. Temperatures this afternoon will be much cooler compared to yesterday. However, highs will remain a few degrees above climo across the Little TN Valley and the Upper Savannah River Valley. Highs elsewhere should end up a few to several degrees below climo thanks to higher cloud cover. Lows tonight will end up near climo to a few degrees above climo. Patchy fog may develop across the NC mountains and Foothills overnight into daybreak Wednesday. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 145 AM EDT Tuesday: The short term looks fairly quiet, as the axis of a deep upper trough will swing east off the East Coast, and upper ridging builds in from the Lower Mississippi Valley Wednesday thru Thursday. At the sfc, dry air will filter in from the north, limiting instability. A light easterly or southeasterly low-level flow may be enough to force a few isolated showers and perhaps a garden-variety tstm or two Wednesday and Thursday aftns in the mountains, but otherwise, it should be partly cloudy with temps slightly below normal. Highs in the mountain valleys and Piedmont will be mainly in the low to mid 80s and lows in the mid to upper 60s. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 230 AM Tuesday...The medium range guidance is in good agreement on a vigorous shortwave diving thru the western Great Lakes Friday, carving out a fairly deep upper trough across the Ohio Valley Saturday, then persisting as a long wave trough across the eastern CONUS into early next week. An associated low pressure system will bring a cold front into the Ohio Valley and possibly crossing the forecast area over the weekend. The front is expected to stall out roughly across the Midlands or Coastal Plain Sunday or Monday. Overall, the front will have limited moisture to work with, but should support scattered to numerous showers and thunderstorms in the NC mountains with help of NWLY upslope flow Friday and Saturday. Downsloping east of the mountains may limit coverage, but support a return of near-normal to slightly above-normal temps. Drier air filters in behind the front Sunday into Monday, lowering PoPs and bringing temps down a couple degrees. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... Key Messages... 1) Scattered Morning Showers with Isolated Thunderstorms Possible for TAF Sites East of the Mountains 2) Scattered Showers and Thunderstorms Return this Afternoon for All Terminals 3) Generally MVFR/VFR Conditions Expected for Most Terminals At KCLT and elsewhere: 12Z TAF period will remain fairly active at least through today. A broken line of showers has develop along and east of the western North Carolina mountains this morning and continues pushing east. Have TEMPOs for -SHRA for all terminals east of the mountains through the morning hours. KAVL will most likely stay dry through the morning hours but have a TEMPO for MVFR cigs and fog around daybreak. KHKY could see IFR cigs develop by mid- morning so have this accounted for in a TEMPO. Elsewhere generally MVFR to VFR cigs and vsbys are expected through the period. Scattered showers and thunderstorms are expected to develop this afternoon and evening so have TEMPOs for -TSRA at all terminals to account for this activity. Wind direction will remain N/NE east of the mountains through the TAF period. Winds at KAVL will be calm to light NW through daybreak before turning more E/NE. KAVL will likely see light and VRB winds tonight as well as the potential for patchy fog. Patchy fog may reach KHKY but confidence on this is low for now. Drier conditions will filter into the region from west to east later this afternoon into this evening, continuing into Wednesday morning. Outlook: Expect mostly diurnal isolated to scattered diurnal convection through Thursday. Coverage of convection increases Friday into Saturday as a cold front approaches out of the west. Patchy fog and low stratus will be possible each night 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...ARK NEAR TERM...AR/PM SHORT TERM...ARK LONG TERM...ARK AVIATION...AR