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FXUS62 KGSP 300243 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 943 PM EST Wed Nov 29 2023

SYNOPSIS
High pressure will linger over the region leading to continued dry weather into Thursday night. Moisture will return from the west beginning early Friday, with rain chances off and on through the weekend as low pressure systems move across the Eastern states.

NEAR TERM /THROUGH THURSDAY/
As of 940 PM EST Wednesday: Temperatures on track with the current forecast as conditions support decent radiational cooling.
Nighttime Microphysics Imagery continues to pick up on areas of high clouds moving into the area in association with an upper-level disturbance over the Four Corners region and Southern Plains. Winds will go mostly light and variable overnight. Expect another cold night across the CFWA. The forecast remains on track with tweaks to temperatures, dewpoints, sky cover, and wind based on current observations and the latest model trends.

Otherwise, height rises continue across the area as a strong area of high pressure off the east coast churns over the Atlantic. Aloft, an area of low pressure develops in the lee of the southern Rockies and swings NE. This will help to set up the next round of precip for the weekend, but remains well out of the area through the end of this near term forecast. For the remainder of the day and into the evening, winds should remain mostly SW, with occasional gusts across the higher elevations. Overnight, winds quickly diminish as become near calm. Thursday, expect a similar story with the winds, light and mostly southerly. Guidance keeps moisture profiles dry and doesn't start increasing until Thursday night. Therefore, no mentionable PoPs during this period. Temperatures will remain cool today across most of the area with highs struggling to reach the 50s. Thursday, expect highs to increase 5-10 more degrees and flirt with the upper 50s and low 60s. Another blustery night ahead with the entire CWA dipping below freezing.

SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/
As of 218 PM EST Wednesday: A compact shortwave trough will be swinging out of the Southern Plains and lifting into the Lower Mississippi Valley by tomorrow night. In advance of this feature, a dry antecedent airmass will be entrenched across the Southern Appalachians with surface high pressure centered off the Carolina coast. Weak southerly return flow on the western flank of the high will help to slowly nudge a warm front north from the coastal plain through the midlands and into the I-85 corridor by daybreak Friday morning. A slug of deep moisture emanating from the Gulf of Mexico will nudge into the region from the southwest as the upper shortwave rapidly lifts into the Ohio Valley. The synoptic pattern will become increasingly disjointed, however, as the upper wave deamplifies and becomes disconnected from an attendant trailing cold front.
Furthermore, the surface low will be filling as it translates beneath upper-level confluence. In fact, heights will actually be rising across the region Friday as sub-tropical ridging amplifies over Cuba into south Florida and the Bahamas. The result of all this will be for the highest rain chances on Friday to remain confined to the southwest mountains and western Upstate, although scattered showers cannot be ruled out at any given location. Onset of precipitation has been pushed back as initial moisture intrusion tomorrow night will be spent saturating the column before any hydrometeors can survive and make it to the surface. Despite weak southerly flow, an in-situ cold air damming airmass will likely get locked in across the foothills and portions of the Piedmont on Friday as the column becomes saturated. Temperatures will be warm enough for all liquid precipitation, but a few instances of sleet will be possible across the mountains on the nose of the surging moisture before profiles warm above freezing.

Heading into Saturday, a rather wet pattern will take shape as the region becomes sandwiched between the previously mentioned ridge over Cuba and a longwave trough axis extending through the Great Plains. This will set up a period of moist southwest flow extending from the Gulf of Mexico into the Mid-Atlantic on the warm side of a stalled cold front draped from western Tennessee through western Kentucky. Persistent warm and moist advection will eventually lead to the demise of the weak in-situ cold air damming airmass, especially without a source of sustained cold/dry air. Embedded shortwave perturbations in the southwest flow regime in concert with favorable upper jet dynamics and 1.25-1.75" PWATs will help blossom an expansive area of precipitation Friday night into Saturday.
Guidance varies as to how far north this activity will spread with the greatest rain chances across northeast Georgia and the Upstate.
50-150 J/kg of elevated MUCAPE may also prove sufficient for a few isolated lightning strikes with any deeper convective cores.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
As of 241 PM EST Wednesday: A perturbed southwest flow regime will continue to foster a wet pattern across much of the region Saturday night through the day Sunday and into Sunday night. Additional rounds of showers will continue to stream across the area, but rainfall amounts will generally remain light. The pattern finally begins to break down Sunday night as a potent shortwave trough dives out of the Northern Plains and into the Mississippi Valley. This will finally help progress the stagnant pattern and kick the trough axis through the area by Monday. Deep moisture will get shunted east of the area with a cooler and drier airmass filtering in behind the cold frontal passage. Global model guidance is in good agreement that another potent wave will drop out of the Northern Plains early next week, but with a lack of deep moisture this system will likely be moisture starved for much of the area. Depending on the track of the low, a period of northwest flow rain/snow showers may grace the mountains. The GFS solution depicts a deep closed upper-low with a favorable setup for a solid northwest flow snow event, but the ECMWF solution is noticeably drier less amplified with the wave. Will advertise a chance for rain/snow showers along the Tennessee border for now until guidance comes into better agreement.

AVIATION /03Z THURSDAY THROUGH MONDAY/
At KCLT and elsewhere: VFR conditions will be in store through the forecast period. High pressure will remain in control as it settles over the Carolinas. Winds are becoming more light and variable this evening, with a few sites still showing a southwesterly component.
Most sites will go light and variable overnight. Some high clouds moving in from the southwest has allowed for prevailing FEW/SCT 250 in the 00Z TAF update. Winds will gradually increase out of the south during the daytime period Thursday, with small potential for low-end gusts during peak heating. High clouds should remain in place through much of the TAF period, with cigs slowly lowering by Thursday night, ahead of the next storm system.

Outlook: VFR conditions prevail as dry high pressure continues into Thursday night. Moisture and associated restrictions will return starting on Friday and lasting through the weekend.

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

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