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FXUS62 KGSP 080544 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1244 AM EST Fri Dec 8 2023

SYNOPSIS
Dry high pressure will continue today before moving off the Carolina coast tonight, with warmer temperatures expected through the early weekend. Expect rain ahead of an approaching cold front from Saturday through Sunday, with thunderstorms more likely on Sunday.
As the rain ends Sunday night, colder air behind the front may produce some light snow in the North Carolina Mountains.

NEAR TERM /THROUGH TONIGHT/
As of 1230 am EST: The observed temperature fall early this morning is lagging behind forecast trends slightly, but still expect forecast mins to be achieved as winds continue to decouple in most areas, and with encroaching high cirrus being mostly thin.

Otherwise, cirrus will continue to spill into the region over a shallow southeastern ridge aloft today, perhaps becoming a bit thicker at times. At lower levels, southwesterly flow will permit maxes to gain one to two categories over observed Thursday values, running some 5 to 9 degrees above climo. Despite the southwest flow, some dewpoint drying is still expected with diurnal mixing, with very dry air near the top of the boundary layer. RH values should remain above critical thresholds for any fire weather concerns today despite the mixing.

Deep-layer southwesterly flow will increase tonight as heights fall from the Upper Midwest to the Plains states. Deeper moisture will begin arriving from the southwest after midnight across the southwest NC mountains. Upglide/upslope flow into the southwest mountains will require improving PoPs through the early morning hours Sunday, perhaps touching low-end likely values in Graham County by daybreak. This initial QPF will be very light.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
As of 115 PM EST Thursday...The upper pattern transitions from a ridge axis to increasing difl flow Sat. This will displace a sfc high off the Atl coast and allow for good moist adv off the Atl and the GOM by the afternoon. Expect enough moisture transport combining with mech lift to produce periods of rain showers across the sw/rn NC mtns and NE GA aft daybreak with little convec potential due the early timing and relatively cool sfc temps.

By Sat night, the atmos become quite dynamic to the west as an acute h5 trof develops across the MS Valley and initiates a stg wavy sfc front over middle TN. This front will be the main weather-maker Sun as it will be supported with high shear thru a deep layer and increasing upper divergence due to coupled jets crossing the area. A pre-frontal trof pushes into the NC mtns arnd 18z (good model consensus on timing) and the overall synoptic forcing will be high enuf to likely produce QLCS even with relatively low instability to work with.

The models continue to indicate arnd 100-250 J/kg of sbCAPE by mid- afternoon ahead of the sfc convg zone, thus a high-shear low-CAPE setup looks to be in store. Expect semi-organized lines of convect capable of producing bowing segments and possible broken-S tors in addition to stg/svr mixed-down straight line winds. The SPC has yet to include an outlook as the event is still Day 4, but the new Day 3 outlook shud have the fcst area in some sort of severe risk. Another issue will be high rainfall amts as the the alignment of strong and deeper cells may linger or train over the same areas while producing high rainfall rates. All in all, this is looking like an event to keep an eye on. Some storm variables will change as we near the event, but right now confidence is abv normal for a sigfnt event to take place.

During the overnight Sun, wrap around moisture will continue and as a colder cP airmass mixes in from the northwest. Expect the development of NW flow snow showers across the wrn NC mtns arnd 00z continuing toward daybreak Mon producing arnd 1-2 inches of accum across the higher elevations. A winter weather advisory may be needed. Highs on Sat will remain abt 5 degrees abv normal and similar highs Sun, except the mtns will see a non-diurnal drop off during the early afternoon behind the sfc front. Abv normal lows Sat night with all the cloudiness and s/ly flow, then a drop-off to the m20s mtn valleys and near freezing over the non/mtns Sun night post FROPA.

LONG TERM /MONDAY THROUGH THURSDAY/
As of 155 PM EST Thursday...A modified cP airmass continues to build across the area Mon and any lingering snow showers across the NC mtns will quickly come to an end due to llvl dry air advection and the orthogonal flow becoming disrupted. The pattern returns quiet over the extended, however, the NC mtn ridges could see black ice issues due to snowfall melting during the day Mon. Surface high pressure is reinforced by a very strong 1040 mb Canadian high diving south on Mon. Good insolation will be had each day, but with this colder airmass slow to modify, max temps will remain generally in the 50s and lows fall into the 20s and 30s each night. Wind chills should not be an issue, even across the higher terrain, as mixed- layered winds remain low end.

AVIATION /06Z FRIDAY THROUGH TUESDAY/
At KCLT and elsewhere: Expect mainly scattered to broken cirrus through the bulk of the current TAF period. Some VFR stratocumulus, with bases at 4 to 5 kft, will begin arriving from the southwest toward the end of the TAF period, with any lower restrictions generally west of the terminals through 06Z Saturday. Southwest winds will exhibit some low-end gusts from KGMU to KGSP to KCLT with mixing after 15Z-16Z today, with sustained winds generally SW to S at 10 kt or less otherwise. All sites will remain precipitation-free through the current cycle.

Outlook: Moisture will return from the SW on Saturday, with some ceiling restrictions becoming possible during the day. Additional restrictions and more widespread precipitation will move in Saturday night ahead of an approaching cold front, with the heaviest showers and embedded thunderstorms possible on Sunday nearer the front. Dry and VFR conditions will return for the early to middle part of next week.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.

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