Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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298 FXUS62 KGSP 091912 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 212 PM EST Sat Nov 9 2024 .SYNOPSIS... Dry high pressure will persist today before a cold front brings rain and cooler temperatures back to the area Sunday afternoon into Monday. Dry high pressure will return Tuesday and Wednesday, before another cold front arrives toward the end of next week. && .NEAR TERM /THROUGH SUNDAY/... As of 204 PM Saturday: Fairly quiet across the region this afternoon, and that is expected to continue as sfc high pressure ridges down from the northeast in what is essentially a dry cold air damming wedge at this point. The lingering stratocu seen on satellite imagery over northeast GA and the Upstate belies the developing southerly flow across the region. Meanwhile, some thin cirrus was streaming in from the WNW. Should be dry into the evening. Temps were in good shape, so no changes are necessary at this time. Over the next 12 hours or so, a transition will take place toward a more productive hybrid cold air damming wedge as the weakening parent high gets pushed off the Mid-Atlantic coast by the progressive nrn stream ridge. The southerly flow will gradually increase tonight with isentropic lift commencing in the early morning hours, altho the moisture takes a few more hours to arrive. But, arrive it should, by daybreak or so with clouds and light precip developing first in the southerly upslope areas of the Blue Ridge Escarpment, and then expanding outward from there during the morning as the isentropic lift improves. The CAMs indicate more shower activity than previous model runs, so the precip chances were bumped up and expanded mainly east of the mountains into the afternoon. Still in the chance range, but trending upward, and suspect that more people will get some light rain than not. Meanwhile, the approach of a cold front from the west will increase the rain chances over the western side of the mtns in the afternoon. This fcst trend also supports more cloudiness, which is more likely to lock in the hybrid wedge, and keep temps below normal. Thus, the high temp was also nudged downward a bit for Sunday afternoon. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 1232 PM EDT Saturday: CAD should begin to erode on Monday. Model soundings depict a shallow wedge still in place early Monday morning, but by Monday afternoon/evening, deep mixing should start to erode the wedge from the bottom up. It`ll be a one-two punch, too, as potent, if short-lived, low-level CAA arrives with a cold front digging across the Tennessee Valley. This should effectively end CAD and allow high pressure to begin building in from the north on Tuesday. This will lead to a period of drying, though the center of the high will be migrated eastward quickly enough that by Tuesday evening, it`ll already be pushing out of the Ohio Valley and into the Adirondacks. So, this will play out as increasing shower activity through Monday morning , leading up to the arrival of the actual frontal circulation Monday afternoon. Rain chances will then diminish Monday night as the boundary pushes eastward. Given the depth of mixing, it`s still not out of the question that we could see a stray surface-based thunderstorm...but even the most aggressive models depict a weak residual cap, severely limiting the strength of any such cell. Drying is then expected through the remainder of the period, with mostly clear skies expected Tuesday. The front will do little to moderate temperatures, which will be in the low- to mid- 70s both afternoons. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 116 PM EDT Saturday: As surface high pressure continues to work its way east under a progressive upper pattern, we`ll gradually revert to a northeast-flow CAD-like pattern on Tuesday and Wednesday. Profiles look to remain dry enough, however, and isentropic ascent weak enough, to preclude the usual dreary weather associated with established cold-air damming. Instead, expect enough afternoon mixing for scattered cloud cover only. Temperatures will climb into the 70s on Tuesday, but by Wednesday, the intrusion of cooler air from the northeast will result in afternoon highs in the mid 60s. Wednesday night or early Thursday, a cold front is still expected to make tracks across the area. This will result in a brief period of showers from Wednesday night through the first half of the day Thursday. Synoptic forcing will be modest at best, and with a weak frontal circulation given how far removed the parent low will be. Behind the front, robust high pressure will build in from the central U.S. This will somewhat decrease temperatures, but the effect will be more noticeable at night - with Thursday and Friday night`s lows falling into the 40s or even upper 30s in some spots - than during the day, when solar heating and weak downslope flow could offset any CAA-induced cooling. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... At KCLT and elsewhere: Weak cold air damming will continue this afternoon and evening, but the air mass will remain dry, so other than some high-based stratocu, not much will be happening. Conditions should remain VFR, with a NE wind at the sfc, well into the evening. Toward daybreak, that will change as moisture arrives from the S and SE. Low ceilings and light precip will develop first along/near the Blue Ridge Escarpment after midnight, eventually expanding to encompass the Upstate terminals and KAVL. Restrictions will develop in those locations after daybreak, beginning mainly as MVFR ceilings. As the moist upglide flow from the south persists, the precip and clouds will expand across the region, bringing the entire forecast area under MVFR, and eventually IFR by the end of the period at KCLT. Outlook: A wedge regime will persist until a cold front passes Monday night or Tuesday. Periodic restrictions and precip are likely Sunday night and Monday. Dry and mostly VFR weather expected Tue-Wed. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...PM SHORT TERM...MPR LONG TERM...MPR AVIATION...PM