Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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180 FXUS62 KGSP 221810 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 210 PM EDT Sun Sep 22 2024 .SYNOPSIS... High pressure will linger across the region the remainder of the weekend, keeping hot temperatures across the board. A more moist airmass will spread over the area on Monday and linger through at least mid-week. && .NEAR TERM /THROUGH MONDAY/... As of 205 PM EDT: An upper ridge axis to our west will become centered over the Appalachians by the end of the period. However, short wave energy is able to top the ridge and move into the area. A dampening short wave overnight and a stronger one Monday. CAMs continue to highlight the area along and west of the I-26 corridor for mainly isolated convection this afternoon and evening. The northern mountains and I-40 corridor are highlighted for isolated convection with the wave overnight. Expect low clouds to spread into the area from the NE toward daybreak. This should limit patchy fog except for the usual mountain valley fog. Lows Ohio Valley could wander toward the southern Appalachians toward daybreak Monday. Lows will be 5-10 degrees above normal. Expect scattered mainly diurnal convection to develop along and north of the I-85 corridor with numerous coverage possible across the mountains. While severe storm chances will be better of TN, instability, shear, and DCAPE values will be high enough for a storm or two to produce damaging wind gusts. Highs will be around 5 degrees above normal. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... As of 129 PM EDT Sunday: Potent subtropical ridging will be in place over the Gulf of Mexico Monday evening, while a longwave trough will deepen over the Great Plains as multiple embedded vort lobes phase together as they move east. This`ll have the effect of driving ridging over the Carolinas eastward on Tuesday, and exposing us to increasingly potent moisture ahead of the advancing trough. Between cloud cover and diminishing thicknesses, temperatures will fall on Tuesday, with highs only climbing into the low- to mid-80s...and scattered showers can be expected across the forecast area. A surprising 1200+ J/kg sbCAPE will develop east of the mountains, permitting some embedded thunder as well. Wednesday, an upper low will cutoff from the main trough and settle over the Ozarks. Meanwhile, a broad baroclinic zone will settle into the central Ohio Valley, apparently stalling somewhere west of the NC-TN border. Based on the latest 12z suite of operational guidance, it should remain far enough displaced from our region that it won`t contribute to significantly high rain chances on Wednesday compared to Tuesday...but we`ll still be locked into a moist air mass, with another round of respectable afternoon instability...so at least widely scattered showers and thunder appear likely. Highs on Wednesday will be similar to Tuesday`s with most locations cooling only a degree or two. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 140 PM EDT Sunday: By Wednesday evening, the bulk of guidance is in agreement on a developing tropical low over the Gulf of Mexico, somewhere west of Cuba. On Thursday and Friday, this system is expected to lift north. The exact configuration of the upper pattern when the system begins to move inland will have a large impact on what impacts are realized here in the Carolinas. Ensemble members with a weaker Ozark low and stronger ridge over the Eastern Seaboard depict the post-tropical system tracking well west of the Carolinas, while members with stronger Ozark lows and weaker east coast ridging depict a more eastward track, which would bring more moisture into the Carolinas. The second solution is the dominant one among the latest LREF cycle, but not by much - there`s still significant support for a more westward track. Having said all this...either solution would bring some moisture into the Carolinas by Friday and Saturday...it`s just a question of how much. With that in mind...spectulating on possible rainfall totals is still a losing game. It`s likely to be rainy Friday and Saturday, but QPF remains low-confidence. Otherwise...the remainder of the forecast is murky, with the evolution of the atmosphere past Friday and Saturday completely dependent on how the tropical system affects our area. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... At KCLT and elsewhere: VFR cumulus this afternoon with isolated convection generally along and west of I-26. Chance still too low for TAF mention. MVFR then IFR stratocu moves SW across the area late this evening and overnight. Have it for the NC sites, where fog may also develop at KAVL and KHKY. There is a chance the cloud deck makes it to KGSP/KGMU, but that is more uncertain so put FEW MVFR for now. Vsby should improve quickly after daybreak, but cigs will take longer to go VFR. Scattered convection expected during the afternoon, so have PROB30 at KAVL where it starts sooner and KCLT wit the longer TAF period. Light N to NE wind becomes through the overnight becomes light S on Monday. Outlook: A weak cold front will slowly approach from the west this week before tracking over the area on Thursday. Chances for diurnal showers and thunderstorms will increase Monday and remain elevated through at least Thursday. A tropical cyclone may move into the SE late in the week. Mountain valley fog/low stratus may develop each morning around daybreak. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...RWH SHORT TERM...MPR LONG TERM...MPR AVIATION...RWH