textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Minor tweaks to Key Message 1 to reflect current conditions. Also updated the aviation discussion to reflect the recent 00z TAF issuance.

KEY MESSAGES

1. Areas of rainfall and/or drizzle expected at times through Sunday, with a risk of isolated flash flooding. 2. Below-normal temperatures and dry conditions expected for most of next week, with little chance for precipitation.

DISCUSSION

Key message 1: Areas of rainfall and/or drizzle expected at times through Sunday, with a risk of isolated flash flooding.

Showers persist over portions of the area this evening as backdoor cold front continues to push SW, now having passed most of the NC Piedmont and entering the Upstate and S Blue Ridge Escarpment areas as of 8 PM. Incipient SW mid- to low-level flow aloft will interact with developing NE surface flow to produce potential for slow storm motion and training, such that some areas may receive multiple rounds of rainfall, or be affected by a protracted period of heavy rain. As a result, hi-res models are in good agreement on an axis of 1-1.5" of mainly convectively-driven rainfall through tonight. Not seeing the greatest consensus from our slate of hi-res models, and continue to note some run to run variability in the HRRR. However, the latest runs still mostly depict an axis of higher rainfall likely associated with the wedge boundary despite not agreeing well on where that would set up; radar mosaic does suggest such an axis is forming from Henderson County across the northern Upstate to the SC Catawba region. This is currently the area most likely to see excessive rain or flash flooding on a local scale. As the backdoor front settles farther south the axis of best rain rates should gradually shift south as well. Overnight as remaining elevated instability is exhausted we expect rain to taper off to areas of drizzle perhaps with a few embedded lighter showers

The pattern will change dramatically into Sunday, as the cold front settles to our south and cold-air damming becomes established across the area. The 12Z suite of CAMs continues to feature a pronounced lull in rainfall from Sunday morning through at least early afternoon, as CAD puts the damper on any lingering convection. That'll be short-lived, however, with a second and somewhat more pronounced shortwave arriving in the central Ohio Valley by afternoon...accompanied by a sharpening upper jet. These features should be well-aligned enough to produce a slug of better synoptic forcing, which should reincite low-level moist upglide during the afternoon, then drive the stalled cold front to our west across the area at last Sunday night into Monday. QPF for this latter portion of the event continues to trend downward...with the operational guidance generally supporting less than an additional inch of rainfall past 12Z Sunday, except for portions of the Upstate south of I-85, which could still be under the gun for training along the wedge boundary, depending on where it sets up. At any rate, it increasingly looks like the areas hit hardest on Sunday will not be the same areas hit hardest today, so if nothing else this should help to curtail the threat of longer-term cumulative hydro issues.

Key message 2: Below-normal temperatures and dry conditions expected for most of next week, with little chance for precipitation.

Not much change to the long-range forecast this afternoon. Still expect the upper pattern to relax beginning Monday afternoon as the remnant shortwave axis and its surface reflection push off to our east, ushering in a drier cP air mass beneath broad and flat flow aloft. CAMs hint at additional sprinkles continuing into the morning Monday as residual moisture is swept out of the area, but even the latest REFS guidance, which seems anecdotally to tend on the aggressive side, depicts only isolated showers past 12Z...plus some lingering NW flow showers along the NC-TN border (but not cold enough for any snowflakes, sorry!) through the evening. It looks therefore like Monday should be a mostly-dry day.

The core of surface high pressure should migrate across the Ohio Valley and off the Mid-Atlantic coast through Wednesday, maintaining below-normal temperatures and mostly clear skies through at least the middle of the week. All the operational guidance and the vast majority of the recent long-range ensembles feature a lingering "pool" of high pressure settling over the Southeast and modifying through the end of the week, resulting in a steady warming trend toward back near normal by Friday. The jury remains out for next weekend, with significant divergence in ensemble solutions past Friday.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Backdoor cold front still in the progress of crossing the terminal area. It does appear to have passed KCLT/KHKY, where winds have turned steadily NE and IFR cigs have developed, under cold-air damming regime. This regime should develop farther SW through Upstate SC overnight. KAVL as usual will be a bit trickier due to its mountain valley position. SCT SHRA are expected to persist at least through this evening, with heavier SHRA causing IFR vsby in some cases, and possibly accelerating onset of IFR cigs, where not already in place. Some variability in cigs should be expected near any SHRA with potential for temporary improvement. An isolated TS is not out of the question though chance too low to warrant inclusion in TAFs. Winds will turn from SE toward NE overnight at the SC sites, while KAVL remains mainly SE if not going light/VRB. Precip should transition to primarily -DZ or steady -RA for a time overnight and most areas will see cigs go down to LIFR. Areas of fog expected to develop though confidence low on it causing worse restrictions than the cigs. A lull in precip activity in the early daytime hours, combined with relatively weak flow aloft, suggests the LIFR cigs may scatter/lift in the morning, but still felt confident enough to maintain IFR. SHRA may redevelop during the afternoon, which could help re-establish lower cigs and/or vsby; otherwise as CAD erosion begins late in the day or evening IFR cigs should persist and IFR vsby return after sunset, and there will be some potential for both to sink back to LIFR and last until Monday daybreak.

Outlook: Improvement to VFR is expected by late Monday. Dry VFR conditions are then expected to persist through the rest of the week.

GSP WATCHES/WARNINGS/ADVISORIES

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