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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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606 FXUS62 KGSP 120609 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 209 AM EDT Fri Jul 12 2024 .SYNOPSIS... A weak tropical low will move inland over the eastern Carolinas on Friday, increasing rainfall chances for areas along and east of Interstate 77. Dry weather returns for the weekend and into the beginning of next week, with a pattern change mid week possible. Above normal temperatures through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 200 am Friday: A weak surface wave near the Carolina Coast is expected to wobble slowly westward through the morning. Associated cirrus will continue creeping in from the east and steadily thicken this morning. 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. 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. The weak surface wave will eventually become 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 through this 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 of our CWA. 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 this 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 later today, the bigger 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 NIGHT/... As of 155 AM Friday: Continuing the summertime pattern with more heat and less rain. Synoptically, The majority of the CONUS remains under high pressure, including the southeast. The Bermuda high off the east coast churns and amplifies into Sunday as does the persistent anti-cyclone over the southwest. Essentially, the CWA is caught in the middle of two dominating areas of high pressure, keeping the area relatively dry and hot. Saturday, a swath of 2 inch plus PWATS remains centered just to the east of the CWA. Guidance from the GFS signals around 1.5 inch PWATS on the eastern fringe, upticking the moisture and heat index in this area. QPF response, however, is dry. Modeled soundings indicate a strong mid-level inversion and dry layer, hindering any notable rainfall. Even if something could form, the boundary layer is also relatively dry given the stout inverted-V shape. Sunday is a similar story, but with less of a mid-level inversion present. This is driven by higher moisture content east of the mountains due to the SW surface flow. Modeled soundings also indicate better mid-level CAPE and a return, but again, rain chances are minimal as QPF response is non-existent. As for any heat index concerns, moisture return is slow and helps to keep values around the low 100s for a few areas south of I-85 and east of the I-77 corridor. Overall, hot and dry for the short term. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 200 AM Friday: The extended term starts off similar to how the short term ended, with a pattern change possible by mid week. Monday and Tuesday, high pressure continues to dominate the lower CONUS and keeps the area dry for the most part. Long term guidance shows little to no QPF response Monday and a small signal over the mountains on Tuesday afternoon. Again, both days have similar modeled soundings with abundant mid-level dry air and an inverted-V in the boundary layer. Confidence for any rain during the beginning of the week is very low. However, a pattern swing by mid-week could be in the works. Long range guidance from the GFS/EURO signal a developing upper low and trough across Canada, north of the Great LAkes. This amplification could lead to height falls across the eastern portion of the CONUS, and spilling into the CWA starting Wednesday. At the surface, amplifying high pressure off the east coast should setup a persistent SW flow and moisture advection into the area. This could start the unsettled pattern with an increase in PoPs, especially over the mountains, through the end of the period. At this time, Thursday and Friday could be the wetter days, but will likely change as the forecast nears. As for temperatures, Tuesday looks to be the hottest day with actual temps reaching triple digits across most of the CWA east of the mountains. Heat index could be a concern, but with dewpoints mixing out during the day, confidence on high heat indices over 105 is low at this time. After Tuesday, temps look to decrease given the height falls aloft, which should provide some heat relief to much of the area. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: VFR conditions are forecast at most sites through the period. The only exception will be at KCLT, as sub- tropical moisture is expected to surge into the area later this morning in association with a developing disturbance near the coast. While low VFR cigs are expected to develop as a consequence, periods of MVFR are possible throughout the day, with those chances increasing later tonight into early Sat. Shower and thunderstorm chances will also increase in the KCLT area from late morning through the afternoon. Tempos for TSRA may be warranted eventually, but for now, confidence in timing and convective coverage is such that VCSH and Prob30s for TSRA will suffice for now. Showers and storm chances droop off sharply west of KCLT...a Prob30 for -TSRA is carried at KHKY during the afternoon, but coverage near KAVL and the upstate SC terminals is expected to be more isolated. Winds will generally favor light NE through the period. Outlook: Convection and possible restrictions will linger into early Saturday in eastern areas. Isolated/widely scattered diurnal showers and thunderstorms are expected Sat through at least the first half of next week...mainly over the mtns. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...CP NEAR TERM...JDL/JPT SHORT TERM...CP LONG TERM...CP AVIATION...JDL