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FXUS62 KGSP 030836 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 336 AM EST Sun Dec 3 2023

SYNOPSIS
Light showers will continue into this morning, before drier air arrives with a cold frontal passage late tonight. Reinforcing cold fronts will cross the region late Monday and then again Tuesday night, with a brief increase in moisture along the spine of the southern Appalachians early Wednesday. Dry high pressure will then allow temperatures to return to near normal by Thursday and rise to 5 to 10 degrees above normal through next Saturday. Next system that may bring significant precipitation arrives Saturday-Sunday.

NEAR TERM /THROUGH TONIGHT/
As of 309 AM EST Sunday: Light shower activity continues across the forecast area in advance of a cold front now entering the Appalachian mountains. Widespread low visibilities have demonstrated a measure of improvement over the last hour or so as shallow prefrontal mixing has set in. A Dense Fog Advisory will nonetheless remain in effect through 8 AM mainly for Blue Ridge Escarpment zones. Elsewhere, visibility problems will be patchier and may improve significantly as the front approaches.
Already, a scraggly line of showers is visible along the boundary pressing eastward toward the forecast area.

The thinking on that line hasn't changed all that much. As the base of a 500mb speed max translates northeast along the Appalachians, bulk shear values will surge to 60+ kts west of I-26. However, HRRR membership is in decent agreement that we'll struggle to produce any surface-based CAPE, likely owing to low-level cooling incited by the rain showers ongoing across the region...and so it'll be difficult to realize all that shear. Instead, convection will be elevated and muCAPE will only reach ~250 J/kg, so convective columns will struggle to make much of an environment which, under different circumstances, would be dynamically favorable for severe weather.
The new HRRR has actually come in with even less sbCAPE in the far western Upstate than prior runs showed...which wasn't much to begin with. So, it's likely that the southwest NC mountains and the Savannah River Valley will hear a few rumbles of thunder between now and daybreak...but the severe risk looks minimal given profiles.
SPC's Day 1 Outlook, which includes mention of only general thunder risk west of I-77, seems reasonable at this time.

The cold front will push east through today, inciting a slow top- down drying trend across the area and passing east of the region by this evening. Fog and low stratus will be slow to clear out this morning...although if present trends continue, there may be less fog to clear out than expected. Breezy WNW winds will set in behind the front. Despite a slug of decent CAA, winds will have enough of a downslope component to basically offset this...allowing highs to creep some 11-14 degrees above normal. Drying will continue into the evening and overnight hours amid increasingly weak W winds, and although a fairly thick cirrus deck should remain in place through tonight...no further rain is expected through daybreak Monday.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
As of 3am EST Sunday: Fairly decent upper shortwave digs into the SE CONUS on Monday, but with limited moisture at low-levels, system is only expected to give limited rain/snow amounts over the mountains. With main forcing of this system passing through Monday afternoon, temps will be warm enough to keep things mostly rain, with only a few hundredths of an inch of that over the mountain peaks. Pretty strong surface low with this system will track eastward north of the Carolinas. This will give elevated surface winds of 10 to 20kts on Monday from the west and southwest. This advection will continue the dry push into the region with dewpoints dropping from the mid 30s on Monday to the low 30s on Tuesday.
Temperatures will be on a cooling trend following the Sunday warmth, but still above normal on Monday and near normal on Tuesday.

Upper flow flattens on Tuesday with next system moving down from the north Tuesday night, again bringing some rain/snow over the mountains, with higher amounts and a larger areal coverage of showers. The Tuesday night system is much more vigorous than that on Monday, but low-levels continue dry with dewpoints continuing to fall into Wednesday and Thursday. Consequently, coverage of precipitation Tuesday night will be limited to non-existent in the foothills and piedmont. Higher elevations, though, could see a tenth or so of liquid equivalent, with possibly an inch of snow up on the mountains.

LONG TERM /WEDNESDAY THROUGH SATURDAY/
As of 3:15am EST Sunday: Major cold front behind system giving some rain/snow to mountains Tuesday night, will cool things down under dry high pressure Thursday and Friday, with temperatures around 5 degrees below normal for the lows and near normal for the highs.
Thursday and Friday will continue dry weather wise, but moisture may finally begin a return on Saturday in advance of what both the GFS and EC models show as a strong synoptic system. Moisture advance ahead of this system, while not extreme, is at least existent. QPF this far out is pure guess work, with the GFS model much lower then the inch or so of rain Saturday and Sunday in the EC model. Both models, at least, have similar timing with a major FROPA Saturday or Sunday. Along with the moisture advection and higher dewpoints Saturday and Sunday, lows temps will also be warmer, and the bulk of precip should be rain (if it happens), with some lighter snow late in the possible event in northwesterly flow behind the front over the mountains and TN state line area.

AVIATION /09Z SUNDAY THROUGH THURSDAY/
At KCLT and elsewhere: Not much change to the aviation forecast early this morning...as widespread low cigs pair with dense fog along the Blue Ridge Escarpment. KCLT currently under the gun for some light showers and associated flight restrictions for the next few hours, with guidance generally not supportive of anything worse than IFR through daybreak. Other terminals, however, can expect LIFR vis and cig restrictions persisting through daybreak, especially KHKY, which will likely hit periods of VLIFR as it did last night. Conditions will generally improve after daybreak as a cold front slides east of the mountains and instigates some drying. Depicted slightly quicker improvement than what much of the guidance is suggesting as it's hard to believe based on forecast soundings that we'll still have solid IFR at noon. Rather, improved things slowly to VFR by noon. Depending on how things evolve over the next 6 hours...this will be re-evaluated with the 12z TAFs.
Anyway, winds will take on a W component tomorrow - first SW, then eventually WNW by mid/late afternoon. Can't rule out some low-end gusts, but nothing out of left field. SCT/BKN high clouds progged to stick around even into tomorrow night.

Outlook: Dry conditions will persis tinto early next week as high pressure builds back into the Carolinas. The next system won't arrive until Wednesday, and very well may not produce active aviation weather outside the mountains.

GSP WATCHES/WARNINGS/ADVISORIES
GA...Dense Fog Advisory until 8 AM EST this morning for GAZ010-017- 018.
NC...Dense Fog Advisory until 8 AM EST this morning for NCZ035>037- 056-057-064-065-068-069-502-504-506>510.
SC...Dense Fog Advisory until 8 AM EST this morning for SCZ101>106.

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