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FXUS62 KGSP 060254 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 954 PM EST Tue Dec 5 2023

SYNOPSIS
Another reinforcing cold front will cross our region early tonight with a brief increase in moisture through early Wednesday morning over the North Carolina mountains, permitting some light rain or snow near the Tennessee border. Dry high pressure will then allow temperatures to warm up through late in the week, before active weather returns for the weekend as a cold front approaches from the northwest.

NEAR TERM /THROUGH WEDNESDAY/
As of 950 PM: Had a little excitement with the showers moving across the Triad with sleet, graupel, and even some small hail. There were some enhanced echoes over the NW Piedmont, so we may have seen some there too, although didn't see any lightning like across the Triad.
Either way, those will move out soon with elevation dependent snow showers moving into the mountains at this time. Wet bulbs are below freezing across the higher elevations, where the Winter Weather Advisory is in place, with warmer temps in the valleys. Expect the precip to ramp up across the mountains in the next few hours with accumulating snow at the higher elevations. Can't rule out another round of sprinkles or flurries moving out across the NW Piedmont overnight. Winds have been up and down across the mountains but those should pick up and become more steady in the next few hours as well. Only minor adjustments to the snow totals and low temps.

Water-vapor imagery shows a broad upper trough digging into the Ohio Valley, associated with low pressure now moving into Indiana. A channeled vort max can be seen embedded within the trough. Ahead of that feature, an area of altostratus will cross our northern zones this afternoon; a few sprinkles or flurries could result but no accum is expected thru sunset. Sfc flow remains southwesterly over the southern Appalachians, although winds will gradually come around to the west in the wake of the initial vort max. The synoptic cold front, now near the Mississippi River, should push into western NC this evening inducing a further wind shift and setting up northwest flow from a more favorable direction, which will continue thru Wednesday.

The shortwave will dig toward the south Atlantic coast thru tonight. The best overall slug of forcing still is expected with the passage of the synoptic scale axis. Altogether the NW winds will remain fairly mild thru the night. Deep moisture becomes sufficient for good ice nucleation this evening in the Smokies, although there will be a dry mixed layer that might keep more of the moisture aloft. In our mountains northeast of the French Broad, the moisture is paltry in the evening but looks better late in the night, when the DPVA will be a factor. Lower elevation accums should be limited by the dry air at the surface but also the mixing keeping temps relatively warm thru the event. The moisture will diminish from the top down after midnight, from west to east, so the better rates will taper off earlier in the Smokies than in the northern mountains. Overall, accumulation is similar to the previous fcst cycle and no change is being made to the extent of the Winter Wx Advisory. One change from previous forecast cycles is the addition of a flurry or sprinkle mention in the NC Piedmont, also dependent on sfc wet-bulb temp, at times tonight. This too looks most warranted in the predawn hours when dynamic lift and high-altitude moisture peak. Lapse rates are not strong enough over a sufficiently deep layer to expect a threat of accumulation, so any flurries east of the mountains should only be a novelty.

Winds will peak below advisory criteria, with mountain areas seeing gusts of 25 to 35 mph at times, compared to 20 to 25 mph in the Piedmont. Shallow moisture will remain in the upslope areas thru most of the day, so we anticipate a cloudy and cold day with high temps near freezing up there. In the Piedmont, skies will trend clearer from late morning onward but with the continuing wind, temps will be several degrees cooler than those Tuesday.

SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/
As of 200 PM EST Tuesday: Dry sfc high pressure will gradually build in from the west Wednesday evening into Thursday morning, allowing any lingering wind gusts to gradually taper off. Clear skies will lead to great radiational cooling conditions Wednesday night, allowing temperatures to drop below freezing across the majority of the forecast area. Thus, if any snow manages to melt Wednesday afternoon across the higher elevations of the NC mountains, black ice may be a concern Wednesday night into Thursday morning. High pressure will be centered over the Southeast by mid-morning Thursday before the center pushes offshore Thursday evening, leading to continued dry weather. Highs will climb into the mid 50s across the lower elevations on Thursday, with highs in the mid 40s to lower 50s across the higher elevations. Cloud cover will gradually increase from west to east Thursday night. With cloud cover expected to limit radiational cooling, lows will be near or above freezing for most locations Thursday night.

The center of the sfc high will remain offshore Friday into Friday night, but the SW periphery of the sfc high will continue to extend into the Southeast. This will allow winds to turn SW'ly, allowing temps to become 5-8 degrees above climo Friday afternoon and Friday night. Despite increasing cloud cover on Friday, highs should climb into the upper 50s and lower 60s across the lower elevations, and the lower to mid 50s across the higher elevations. Lows Friday night will be above freezing nearly everywhere, with the exception of the highest ridgetops. Moisture will gradually increase out of the west ahead of an approaching cold front Friday night, but precip chances look to remain well to our west through the short term.

LONG TERM /SATURDAY THROUGH TUESDAY/
As of 230 PM EST Tuesday: An upper trough will progress east out of the central US this weekend, developing a negative tilt as it approaches the western Carolinas Sunday evening into Sunday night.
This will drive a cold front across the forecast area sometime Sunday, allowing shower and thunderstorm chances to increase. Rain chances look to maximize Saturday night into Sunday afternoon per the latest global model guidance, thus have likely to categorical PoPs during this timeframe. Depending on the timing of the cold front, severe weather could become a concern Sunday afternoon and early evening. The 12Z GFS shows the front pushing east of the area by Sunday afternoon, while the 12Z ECMWF does not have the front pushing through until Sunday evening. If the ECMWF were to pan out, this would increase the severe wx potential. If the GFS were to pan out, this would decrease the severe wx potential. Needless to say, confidence is low regarding the severe potential on Sunday with global models not in agreement on the timing of the cold front. Rain may transition to snow across the western NC mountains behind the FROPA as temps drop below freezing late Sunday into early Monday morning. Elsewhere, temps will remain above freezing allowing for all liquid precip. Precip chances will gradually taper off Sunday night into early Monday morning as the cold front pushes east of the western Carolinas. Sfc high pressure will build in behind the departing front early next week leading to drier conditions. Temps will remain well above climo Saturday into Sunday, with highs in the low to mid 60s expected east of the mountains. Temps drop to near climo values Sunday night into early next week behind the FROPA.
Thus, highs should drop back down into the low to mid 50s east of the mountains early next week.

AVIATION /03Z WEDNESDAY THROUGH SUNDAY/
At KCLT and elsewhere: VFR except at KAVL. Winds are still SW for KCLT and the SC sites with wind shift in the 02Z to 03Z range. Winds will be WNW at KHKY soon with KAVL already NNW with low end gusts.
VFR stratocu is spreading across the area with cigs at KAVL developing this evening and off and on at KHKY. May see a few VFR stratocu from time to time across the rest of the area. Cigs fall to MVFR overnight at KAVL until 15Z or so when they lift to VFR and scatter out. Can't rule out some sprinkles or flurries at KAVL or even KHKY as well. Gusts may pick up at KAVL overnight but more likely near daybreak. Gusts develop after daybreak across the rest of the area. Skies clear through the day with gusts tapering off for all but KAVL by late afternoon.

Outlook: VFR should prevail through the rest of the week. The next chance for restrictions and precip will be this weekend as low pressure develops and passes NW of the region.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...Winter Weather Advisory until 4 PM EST Wednesday for NCZ033- 048>052-058.
SC...None.

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