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FXUS62 KGSP 110546 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1246 AM EST Mon Dec 11 2023

SYNOPSIS
Northwest flow moisture into the North Carolina mountains will dry up through the morning hours. Dry high pressure will build in from the west today and linger over the area through Tuesday. A dry backdoor cold front will arrive from the north on Wednesday, with reinforcing high pressure returning through late week.

NEAR TERM /THROUGH TONIGHT/
As of 1240 am EST Monday: Regional radars show the back edge of the precipitation shield gradually moving east of the I-77 corridor early this morning. Clearing has been slowed somewhat by the increasingly negative tilt of the passing upper trough. Fortunately, instability aloft and associated precipitation rates are not territory impressive (even though the radar rates look impressive given the bright banding effects from the melting layer.) Still cannot rule out a brief mixover to light snow showers in the northwest NC Piedmont right before the precipitation ends early this morning. The main precipitation issue going forward will be continued scattered snow showers in the northwest upslope flow into the NC mountains. There appears to be a lull presently in this activity, but some resurgence is possible through daybreak- as suggested by upstream IR enhanced cloud top temperatures of minus 10 to minus 12 degrees C. The current Winter Weather Advisory has this well covered, and any locations outside of the advisory in and near the high terrain will keep an SPS mention of black ice and slippery roads this morning. The NW flow moisture should become very shallow through the late morning hours, with any snow showers quickly diminishing to flurries.

The pressure gradient has maximized this morning and will steadily relax through the afternoon hours, with a surface high pressure center building over the southern Appalachians by tonight. Some NW flow gusts of 30 to 40 mph will linger in the mountains this morning before diminishing. Cyclonic curvature persists in the upper flow pattern through the period, with some channeled vorticity moving through the area but producing little more than passing cirrus.
Max/min temperatures for today and tonight should run about 5 to 10 degrees below climatology.

SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
As of 145 pm EST Sunday: An already-low amplitude long wave trough will steadily flatten over our area through the short term.
Sprawling surface high pressure associated with confluent flow aloft covering much of the eastern half of the country will otherwise dominate our weather through the period. Below normal temperatures and dry conditions are therefore expected from Mon night through Tue...before conditions moderate to slightly-above-normal conditions for Wed.

LONG TERM /WEDNESDAY THROUGH SUNDAY/
As of 155 pm Sunday: A rather high-amplitude upper air pattern will be in place at the start of the extended...with a trough centered just off the East Coast, a ridge across the Canadian Rockies, and a cut-off low undercutting the ridge across the Four Corners region. A cold front associated with a short wave trough digging across New England will reinforce sprawling surface high pressure and dry/relatively cool air early in the period. Temperatures are in fact forecast to be below normal Wed night through Friday night.

Forecast uncertainty escalates for next weekend, as global models aren't quite sure what to do with the Four Corners upper low. They do agree that this feature will kick out over Texas by the end of week, as a kicker short wave trough rides through the long wave ridge across the northern Rockies. However, how things evolve from there is where the controversy arises. The GFS phases the kicker wave into the upper low over the Southeast...producing a rather blockbuster coastal cyclone next weekend. The ECMWF and Canadian maintain more of a split flow, with the kicker wave traversing the northern Conus, and the upper low wobbling into the Gulf of Mexico.
The GFS solution would bring another round of precip to the forecast area, while the latter two solutions would keep any precip suppressed to our south. If anything, there may be a slight trend in the global guidance toward the GFS scenario (which has been quite consistent from run-to-run). As such, token chance PoPs appear warranted Saturday through Sunday. Temperatures are forecast to near-climo through the latter half of the period.

AVIATION /06Z MONDAY THROUGH FRIDAY/
At KCLT and elsewhere: Lingering showers at KCLT will diminish quickly by 07Z as the final rand band of the system moves east. All terminals will be dry going forward, with NW flow moisture unlikely to produce anything more than MVFR cigs at KAVL. Gusts above 30 kt will be common at KAVL this morning, and gusts to near 20 kt will be possible at times east of the mountains until the gradient begins to relax later this afternoon. Anticipate little more than FEW to SCT cirrus aloft the remainder of the period once the early morning precipitation moves east of KCLT and the NW flow moisture diminishes at KAVL. Winds will turn more northerly through tonight as high pressure builds across the Appalachians.

Outlook: Dry high pressure will persist through Friday.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...Winter Weather Advisory until noon EST today for NCZ033-049- 050.
SC...None.

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