textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation forecast was updated to reflect the impending 12Z TAFs.

KEY MESSAGES

1. A relative lull in rainfall is expected the rest of tonight through most of Sunday, before the next round of rainfall arrives Sunday night. Dense fog will also be an issue through Sunday morning. An SPS for Dense Fog is in place for the entire forecast area through daybreak. 2. Unsettled weather continues for the foreseeable future, as the synoptic pattern remains stagnant and the Carolinas remain trapped within a moist air mass.

DISCUSSION

Key message 1: A relative lull in rainfall is expected the rest of tonight through most of Sunday, before the next round of rainfall arrives Sunday night. Dense fog will also be an issue through Sunday morning. An SPS for Dense Fog is in place for the entire forecast area through daybreak.

Conditions are still mostly quiet this morning, but low stratus and fog as thick as pea soup has enveloped most of the region. The bulk of the forecast area remains socked into in situ cold air damming, with patchy dense fog and visibility ranging from less than a mile to 1 miles in most locations. Showers have been few and far between, though intermittent light drizzle has persisted most of the night. An SPS for Patchy Dense Fog remains in place through 9 AM this morning, by which time visibilities should mostly improve.

Mostly quiet conditions will persist through the bulk of today, with frequent drizzle and a few isolated showers expected the first part of the day. Can't rule out a few afternoon thunderstorms, though these would *most likely* be elevated in nature as the wedge will persist for much of the day. The big question for Sunday will indeed be: how much will the wedge erode, and how quickly? There's little remaining synoptic support, and guidance doesn't really depict any upper features that'd prompt any periods of better upglide throughout the day. Without much rainfall to support diabatic cooling, the only reason to think it'll remain in place is that there's no discernible mechanism to scour it out. Referring back to the "pea soup" analogy above, however, the most likely scenario seems to be that some shallow afternoon mixing will help to somewhat improve fog and cloud cover conditions again today, but not enough to break the wedge-top inversion at most locations, and therefore not enough to expose us to any good surface-based instability.

Tonight, a weak shortwave embedded within SWly z500 flow will slide across the Appalachians, reinvigorating low-level upglide. Hi-res guidance variously depicts a loosely-organized band of convection making tracks across Georgia late Sunday and arriving in our southwestern zones after sunset, then pushing across the area through the first half of Sunday night. QPF response looks limited - generally less than inch for most zones, and perhaps up to 1.5 inches in parts of the upper Savannah River Valley, per the 00Z HREF - but even without heavier precipitation or widespread convective rain rates, it should help rejuvenate whatever is left of the wedge by this point, and another night of widespread low stratus and patchy dense fog is looking increasingly likely.

Key message 2: Unsettled weather continues for the foreseeable future, as the synoptic pattern remains stagnant and the Carolinas remain trapped within a moist air mass.

Long-range models are coming into increasing good agreement that a more potent shortwave will arrive on Monday night and spur another round of heavier rainfall, perhaps with some elevated convective rates developing within it. Can't begin to express more than moderate confidence until we start getting hi-res ensemble guidance that extends past 00Z Tuesday, but the guidance we do have pretty consistently depicts the ingredients needed for our next wave of rainfall. To wit, the operational models tend to depict anywhere from 0.5 to 1.5 inches of rain falling across the area on Monday night, with corridors of closer to 2.5 inches possible mainly in the SC Upstate. Long-range ensembles mostly agree here, and the most recent LREF cycle doesn't really depict ANY scenarios where we don't get at least a healthy half inch plus.

Otherwise...there's no end in sight, as the synoptic pattern shows no sign of quieting. By mid-week, a weak upper low initially centered near the Gulf Coast should lift into the central Mississippi Valley and begin to weaken. This signal suggests a possible downtick in these successive shortwaves that keep bringing us round after round of rainfall, but as stubborn subtropical ridging and a stagnant Bermuda High remain in place off the Southeast US coast...moisture will continue to advect into the Carolinas, and the potential for more rain will continue.

AVIATION /10Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Widespread LIFR ceilings this morning, with mainly IFR visibility in place, as in situ cold air damming lingers across the region. Shower coverage is virtually nil, though intermittent light drizzle continues all over the place. After daybreak, the thinking remains that the wedge will at least partially erode through the day, permitting slow but steady improvement to MVFR during the afternoon hours...perhaps even very brief, intermittent, low VFR. Isolated to widely scattered showers, maybe even a thunderstorm or two, will be possible during the latter half of the afternoon into the evening. This'll further assist in raising ceilings, though any areas of heavier rain would reduce visibility there. Wherever the wedge erodes and conditions improve, there's potential for winds to become more ESE instead of NE...but they'll remain light 3-6kts through the day.

Conditions should crash again this evening. Most hi-res guidance depicts a band of heavier SHRA with embedded TSRA arriving in the Upstate by 03Z or, then pushing northeast across the area through 07Z. In its wake, widespread LIFR ceilings and reduced visibility will once again develop at all the TAF sites.

Outlook: The pattern will remain unsettled and murky for the foreseeable future, with widespread diurnal convection, often persisting into the overnight hours, and lowered visibility and ceilings each night.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.