textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Aviation discussion updated for 00Z TAF issuance.

KEY MESSAGES

1. Rain chances remain elevated through tonight as the remnants of Arthur track across the region. The main hazards with this system are heavy rainfall capable of producing isolated flash flooding and isolated severe storms capable of producing damaging wind gusts. However, there will also be an isolated tornado threat, mainly along and south of I-85. 2. Increased Fire Danger through 6 PM this evening across the North Carolina Piedmont. 3. Following a stint of dry and pleasant weather on Saturday and the first half of Sunday, we'll settle back into a typical summertime pattern, with warm, muggy conditions. Showers and thunderstorms are expected each afternoon from Monday onward.

DISCUSSION

Key message 1: Rain chances remain elevated through tonight as the remnants of Arthur track across the region. The main hazards with this system are heavy rainfall capable of producing isolated flash flooding and isolated severe storms capable of producing damaging wind gusts. However, there will also be an isolated tornado threat, mainly along and south of I-85.

The remnants of Arthur will steadily lift northeast across the Deep South this evening as a cold front approaches out of the northwest. The remnants of Arthur will track across the western Carolinas and northeast Georgia late this evening into early Friday morning before the cold front pushes across the area behind the remnants on Friday. Convection has become widespread across the area this evening, and this is expected to continue into the overnight. This storm system will be capable of producing isolated severe storms as well as isolated flash flooding.

The main hazard with any severe storms that develop is damaging wind gusts. However, there will also be a low-end and conditional isolated tornado threat. Timing for severe storms still appears to be from now through around 2 AM Friday. The severe risk was upgraded to a Slight risk across the North Carolina Piedmont and along and south of I-85 in South Carolina and northeast Georgia. A tornado risk was also added, mainly along and south of I-85, where a small area of storm relative helicity of 200+ J/kg is expected to develop in the vicinity of a meso-low developing in association with Arthur's remnant core. A Marginal risk remains in place elsewhere. The tornado threat will be highly conditional and dependent on the exact timing and location of the 850 mb LLJ as well as how much instability remains in the wake of ongoing convection.

As for the isolated flash flood threat with the remnants of Arthur, 1.5-2"+ PWATs are in place thanks to low-level southwesterly flow pulling in rich moisture from the Gulf. This will allow moderate to heavy downpours to develop at times this evening into early Friday morning. NBM trended up with QPF through Friday morning but it still appears too low compared to the 12Z high-res guidance. Thus, blended in 20% of the NBM 90th percentile QPF for this evening and tonight to better match up with the latest high-res trends. Ended up with 1.5-2.5" across the southern Blue Ridge Escarpment, northeast Georgia, and the South Carolina Upstate with lower amounts still expected along and north of I-40. 12Z high-res guidance is still split on where exactly the axis of heavy rainfall will occur. For now, it appears that anywhere from the southern Blue Ridge Escarpment down to northeast Georgia and the South Carolina Upstate will have the best chance to see locally higher rainfall totals of 3- 4"+. The 12Z CAMs are still split on whether the axis of heaviest rain will fall along and just north of I-85 or along and just south of I-85. So, confidence is low regarding the exact location of the axis of heavy rainfall, thus a Flood Watch will not be issued at this time. Although most of the ensemble guidance show low probabilities of >3" of rainfall through early Friday morning, we cannot rule out the potential for scattered flooding issues, mainly along/near I-85 but confidence remains low and will depend heavily on where the axis of heavy rain sets up.

Due to the low confidence on where exactly the flash flooding threat will occur, as well as whether the tornado threat will materialize, stay weather aware and make sure you have multiple ways to receive warnings, especially with the flash flood and tornado threat linger through late tonight.

Key message 2: Increased Fire Danger through 6 PM this evening across the North Carolina Piedmont.

In coordination with WFO RAH and the North Carolina Forest Service, a Special Weather Statement for Increased Fire Danger remains in effect across the North Carolina Piedmont through 6 PM this evening despite relative humidity values remaining above critical thresholds (>30%). The main concern with fire weather this afternoon and early evening will be the combination of ongoing drought, dry fuels, and gusty southwest winds (25-35 mph) working together to lead to an increased risk of fire ignition and adverse fire behavior.

Key message 3: Following a stint of dry and pleasant weather on Saturday and the first half of Sunday, we'll settle back into a typical summertime pattern, with warm, muggy conditions. Showers and thunderstorms are expected each afternoon from Monday onward.

By Saturday, a weakening frontal zone will be located just to our south. A few of 12Z CAMs depict some showers, perhaps even a rumble of thunder, south of I-85 Saturday afternoon, but generally think the influence of building high pressure across the Mid-Atlantic will keep convective threat limited...and severe threat virtually nil. Highs on Saturday will top out around or perhaps a degree or two below normal. By all accounts, a pleasant day!

On Sunday and Monday, a series of de-amplifying z500 shortwaves will dig out of the central Great Plains. Synoptic guidance is in good agreement that these waves will generally track across the central to upper Ohio Valley, remaining embedded within the stronger upper flow to our north through the first half of the week. As a result, there's no real impetus for any severe risk Sunday, Monday, and Tuesday, with only typical summertime diurnal convection anticipated.

By Wednesday and beyond, the upper pattern will become more amplified, as troughing deepens over the Midwest and heights fall across the Carolinas in response. There's not much ensemble consistency in depicting any specific impulses on Wednesday thru Friday...but the pattern will be such that a shortwave or two may eject out of the Ozarks and cross the area late in the week...possibly resulting in an uptick in convection and severe chances. Confidence remains low, however, on anything more than typical summertime afternoon showers and thunderstorms.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Convection has become widespread across the Terminal Forecast Area this evening, with at least tempos for TSRA warranted at all sites except KHKY until late evening. Although TS are expected to become less common during the overnight, periods of moderate-to-heavy SHRA are expected through the pre-dawn hours, as the remnants of Tropical Storm Arthur pass over the South Carolina Piedmont. IFR visby will accompany bursts of heavier rainfall, while cigs are expected to gradually lower to IFR at most sites overnight. However, convective activity could result in highly variable cigs from late evening into the early part of the overnight. Cigs are expected to improve quickly around sunrise, as flow turns NW/downslope in the wake of surface low pressure. VFR is expected for much of the daylight hours. A few showers or a storm is possible during the afternoon, mainly across upstate SC.

Winds remain gusty from the SW this evening...enhanced by convective outflow. Gusts should relent by late evening, with winds turning toward the E or SE in advance of the surface low later this evening, then turning toward the W and NW in the wake of the low late tonight. Winds remain NW through the day Thursday, with some afternoon gusts to around 20 kts possible at KAVL

Outlook: A cold front may trigger shower and thunderstorms Friday afternoon and evening, mainly along and south of I-85. Dry and relatively inactive weather returns Friday night into Saturday night. Afternoon and evening showers and thunderstorms should return each day Sunday into early next week.

GSP WATCHES/WARNINGS/ADVISORIES

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