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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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750 FXUS62 KGSP 171018 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 618 AM EDT Wed Jul 17 2024 .SYNOPSIS... Hot high pressure will weaken over the region today. A pattern change begins to evolve by Thursday, as a cold front approaches from the northwest, then becomes stationary across our region for several days. This will keep shower and thunderstorm chances elevated through at least early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 545 AM Wednesday: No major changes for the morning update as the forecast is on track. There is some low level stratus and fog that has formed across portions of the western NC mtns. This should diminish after daybreak. Otherwise, forecast is on the downward trend for heat and a pattern change emerges. Hot temperatures and high pressure stick around a tad longer in the near term, with weak flow aloft. A steady stream of moisture advection from the SW sfc winds persist and prime the area for a more active pattern later in the week. Outside of some low-level stratus over areas that received rainfall yesterday, not expecting too much in the way of overnight cloud cover. By Wednesday morning, daytime heating increases instability throughout the day. Guidance from modeled soundings show around 1500 J/kg of sbCAPE with steep sfc based lapse rates. CAMs hint at another round of scattered showers and thunderstorms possible, with the highest chances over the mountains (70%-85%) and elsewhere (45%-70%). Storm chances could also contribute to heat relief as well. Wednesday highs are still on track for the mid 90s and heat index values hover around 100. A few showers linger into Wednesday night as well. Overnight temps will remain elevated in the low to mid 70s and be muggy. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 250 am Wednesday: A full-latitude upper trough will extend from east Texas through the Great Lakes at the start of the period. The leading edge of an associated baroclinic zone will sag into the CWA on Thursday and provide a focus for increased coverage of showers and thunderstorms during the afternoon and evening. Instability should be sufficient to support a small threat for isolated pulse severe storms. However, the main threat should be locally excessive rainfall, as precipitable water values will meet or exceed 2", while boundary-parallel flow will support the potential for training cells. The boundary could push south of the area Thursday evening. However, a split flow regime will evolve during the latter half of the short term, as the northern portion of the upper trough passes north of our region, and a southern piece becomes separated from the main branch of the subtropical jet and persists across east TX/the lower Miss Valley into the extended period. The pattern will result in the surface boundary becoming quasi-stationary in or near the forecast area, while deep SW flow will support continued high moisture levels across at least the southern half of our area. Scattered to numerous, mainly diurnal convection is again expected on Friday, warranting 50-70 PoPs across much of the CWA. Increased cloud cover...along with advection of lower theta-E air into northern portions of the area, will result in a significant cooling trend... with max temps forecast to be almost 5 degrees below climo. Cooler conditions/limited instability will temper the pulse severe storm risk, but there may be an uptick in the excessive rainfall threat, with the potential for training cells continuing in the vicinity of the boundary. While convection will have a diurnal tendency, the pattern will be such that some degree of activity...and attendant excessive rainfall threat...will continue into Fri night. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 325 am Wednesday: Only gradual changes in the upper pattern are expected during the medium range...as a trough over the lower Miss Valley slowly retrogrades, while an intensifying subtropical ridge builds into the Southeast from the western Atlantic. For at least the first half of the period, a weak baroclinic zone will persist over the Southeast, while deep SW flow will support a continued supply of Gulf of Mexico moisture. As a result, the weekend will remain very active convectively...primarily diurnal in nature, but with some activity lingering well beyond the afternoon maximum. Convective activity could begin to taper down early next week as the ridge attempts to assert influence. However, a consensus of guidance suggests above-climo PoPs for diurnal convection are in order through Day 7. Slightly-below normal temps are forecast through the period. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... At KCLT and elsewhere: Prevailing VFR conditions for the TAF period. KAVL and KHKY had BR overnight and should start to see improvements after 12z. Calm and quiet weather for the morning hours until the afternoon. Another round of convection is slated during peak heating once again. Confidence is moderate for showers and TSRA, so a PROB30 at most sites, with TEMPOs for TSRA at KAVL, KCLT, and KHKY where confidence is higher. G30 at KCLT is a possibility if any storms form near the terminal, which is also accounted for in the TEMPO. Winds should prevail SW outside KAVL, which will toggle N/S, but all sites will have light winds outside any areas of TSRA. Overnight, expect patchy BR/FG in areas that received rain today. Vsby restrictions at KAVL are likely to dip down to LIFR again. Outlook: Morning fog/low stratus possible each morning, especially across the mountain valleys and for areas that received heavy rainfall the day prior. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JDL NEAR TERM...CP SHORT TERM...JDL LONG TERM...JDL AVIATION...CP