textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Severe Thunderstorm Watch in effect for Upstate SC and some adjoining counties of GA and NC until 9 PM EDT.

KEY MESSAGES

1. Scattered showers with heavy downpours may redevelop overnight and could cause isolated flash flooding, especially over the mountains. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans. 2. Rain chances linger Monday before drier conditions return Monday night, persisting through mid-week. A cold front will bring rain chances back towards the end of the week.

DISCUSSION

Key message 1: Scattered showers with heavy downpours may redevelop overnight and could cause isolated flash flooding, especially over the mountains. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans.

Instability will wane nocturnally this evening, though lapse rates remain favorable for some degree of elevated convection. As the front sags farther south and high pressure builds from the Great Lakes into the mid-Atlantic, low-level flow turns more easterly; overall slow storm motion will continue, but flow aloft remains westerly and this suggests remaining convection may "anchor" along east-facing terrain. PWATs will trend downward slowly from north to south following the advance of the high pressure, though not fast enough to preclude a threat of isolated flash flooding, particularly due to the anchoring or where the overnight precip amounts to a second round of heavy rain, following storms this afternoon. WPC also features a Slight Risk for an area east of the Blue Ridge Escarpment and nearest the overnight position of the front as a result.

Key message 2: Rain chances linger Monday before drier conditions return Monday night, persisting through mid-week. A cold front will bring rain chances back towards the end of the week.

Easterly low-level flow continues Monday as the front settles to our south and we come under the influence of a somewhat wedge-like surface high nosing south into the region. Areas of fog and low stratus may linger well into the morning though clouds are expected to scatter over much of the Piedmont for the afternoon. A few showers may linger though with lower PWATs and far less instability, the threat of heavy rain is much lower. Temperatures will trend 10- 15 degrees cooler, with maxes in the mid-70s to lower 80s. We remain fairly humid through this period. PoPs fall to 10% or less for most of the area Monday night and remain low through Wednesday night. Temperatures do moderate as heights rise aloft and the sfc high sets up offshore, nearly back to normal Tuesday and then slightly above normal Wednesday.

Subtle upper height falls do begin over the Appalachians again Wednesday night as a mature cyclone moves across central Canada, pulling the next front into the mid-MS and OH valleys. Slight return flow develops in advance of that feature, warranting chance PoPs returning for the mountains on Thursday. Some of the global models, especially the Canadian GDPS, show the surrounding broad trough inducing a wave along the stalled front, generally near south Georgia, with small PoPs also being warranted for the lower Piedmont on Thursday as a nod to that possibility. 40-60% PoPs expand to the whole area Friday near the Ohio Valley cold front. The orientation of the front is not especially conducive to a strongly forced severe weather event, and destabilization appears limited ahead of it. Quasi-zonal upper flow persists into next weekend so the front could stall near the region and maintain unsettled weather. Seasonably warm and muggy conditions should continue.

AVIATION /00Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Lingering VCSH and SHRA through 06z is possible at most terminals, 07z at KCLT. After 06z, cig restrictions across most terminals (not KCLT) with IFR restrictions through mid morning. Confidence in BR is highest at KAVL so a TEMPO from 10z-14z for 3/4SM vsby. Stratus should clear out as winds pick up after 14z. Winds remain NE through the period with gusts of 15-20 kts during Monday afternoon and tapering by the end of the forecast period.

Outlook: Drier conditions return by Monday night, lingering through mid-week. This should allow VFR to return outside of morning mountain valley fog and low stratus.

GSP WATCHES/WARNINGS/ADVISORIES

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