Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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112 FXUS62 KGSP 120237 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1037 PM EDT Thu Jul 11 2024 .SYNOPSIS... A weak tropical low will move inland over the eastern Carolinas on Friday then further north over the weekend. This will enhance rainfall for areas along and east of Interstate 77 mainly Friday and Friday night. Above normal temperatures and daily isolated to scattered afternoon and evening showers and storms are expected from Sunday through the middle of next week. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 10:15 PM EDT Thursday: A coastal baroclinic zone continues to slide westward late this evening as a sfc wave slides north along it. More dense cirrus already creeping in from the east will steadily thicken overnight. The increasing cloud cover will help keep temperatures warmer than last night, with lows expected to bottom-out slightly above climatology outside the mtns and slightly below climo over the mtns. Winds have gone light to calm at most sites and should remain that way into the morning. Otherwise, we will remain sandwiched between broad upper ridging to our east and to our west, while lower amplitude upper trofing lingers to our north over the Great Lakes. At the sfc, weak and poorly organized low pressure will linger over the SE Coast thru the day on Friday. It will eventually get absorbed in the broader SLY low-lvl flow courtesy of the much larger Bermuda High as the period ends early Saturday. This will result in deeper moisture spreading further westward and into our eastern zones overnight and Fri morning. Profiles should be moist enough that lower and thicker clouds develop over the I-77 corridor along with increasing rainfall chances by late morning. The latest CAM guidance continues to depict isolated to sct convection over the I-77 corridor during the afternoon hrs, however the better coverage and the more robust cells appear to remain just to our east and over RAH`s fcst area. Nonetheless, most of the latest model profiles still produce about 500 to 1000 J/kg of sfc-based CAPE over roughly the eastern third of our CWA for Friday aftn/evening. This CAPE does appear to be fairly "tall and skinny" which makes strong to severe thunderstorms less likely. As such, the svr potential still looks minimal across our CWA thru the period. With PWs of 2+" or higher over our eastern zones on Friday, the bigger potential threat may be locally heavy rainfall. Having said that, WPC`s Day 2 Slight Risk for excessive rainfall remains to our east. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... As of 211 PM Thursday...The short term forecast period starts off tomorrow night with a sharp upper shortwave trough over the eastern Great Lakes and stout upper ridging over the Atlantic. A weak surface low is also progged to have moved inland over southeast Georgia with a subtle inverted trough extending across the Coastal Plain. Persistent onshore flow will have pushed the previously stalled frontal boundary west back into the I-77 corridor. Afternoon showers and thunderstorms on the moist side of the boundary may linger into the early evening hours, but will dissipate shortly after sunset with loss of daytime heating. Heading into Saturday, the surface pattern becomes more nebulous as the upper trough axis passes by to the north. This will in turn allow low-level flow to shift to out of the west/northwest with the boundary sliding back east again. This will shunt the deeper moisture plume back east as well with PWATs falling to around 1.5" or less. A lack of deep moisture will greatly preclude coverage of diurnal convection through the weekend with any cumulus/weak updrafts struggling to deepen in the face of substantial dry air entrainment. A couple isolated showers and storms cannot be discounted, but this will be the exception and not the rule. Temperatures will continue to warm through the period with highs climbing into the mid to upper 90s. Deep mixing within the drier airmass will mix out dewpoints, thus while several readings with heat indices in the low 100s are possible, heat advisory criteria (105 degrees) isn`t expected to be reached through the weekend. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 237 PM Thursday...Unfortunately, next week doesn`t start off with any good news. A perturbed belt of westerlies will extend from the Great Lakes into New England. The Southern Appalachians will be situated south of the base of broad troughing with upper ridging building into the region from the Southern Plains. Heights will rise through the beginning of the week with warming low-level temperatures. Low to upper 90s will be common on Monday with a couple readings touching the century mark. Tuesday appears to be the hottest day of the period with widespread mid to upper 90s and numerous low 100s possible. The good news, however, is that dewpoints should mix out into the low to upper 60s each afternoon which will keep heat indices in check. Low 100s to near 105 will still be possible though and heat advisories may ultimately be needed. Subsidence and a lack of moisture will limit diurnal convection with below average PoPs and only isolated coverage expected. A pattern change will be on the horizon by mid week as a potent longwave trough becomes established from the Hudson Bay into the Ohio Valley. An attendant surface cold front will be dropping across the Midwest on Wednesday and encroaching on the Appalachians by late week. Ridging will also slide to the east which will allow for return flow off the Gulf and Atlantic to advect rich moisture back into the region. The net result will be a noticeable uptick in PoPs Wednesday through Friday, especially as the front stalls just west of the area. One more day of heat and humidity may continue into Wednesday, but will be conditional on timing and coverage of showers and thunderstorms. Should this wetter pattern change hold, most of the area should hopefully see some much needed rainfall mid to late next week. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: Expect VFR conditions to continue at all taf sites thru the 00z period. The only exceptions will be at KCLT where there is a decent chance that MVFR cigs will spread over the terminal late tomorrow (Friday) morning. Expect the lower cigs to lift to low-end VFR by the early afternoon. In addition, a weak coastal low will spread showers and thunder- storms westward tomorrow with KCLT the most likely to see pre- cip from this system. For the time being, I have a combination of VCSH and a PROB30 for TSRA for KCLT and KHKY. The other ter- minals are less likely to see showers and/or thunderstorms so I just have VCSH and VCTS for them. Otherwise, thickening cirrus will persist over the area well into the overnight hrs as winds become light and most sites. Outside the mtns, winds will remain N to NELY thru tomorrow aftn and veer to more ELY by tomorrow evening. At KAVL, winds will go light and vrb later tonight and remain light thru the rest of the period, generally favoring an ELY to NELY direction thru the day tomorrow. Outlook: Rain and possible restrictions will linger into early Saturday. Sct diurnal showers and thunderstorms will be possible over the weekend and into the first part of next week. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...JPT SHORT TERM...TW LONG TERM...TW AVIATION...JPT