textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes except for 00z Aviation discussion.

KEY MESSAGES

1. Hot and humid conditions with heat index values ranging from 100 to 106 degrees again Sunday afternoon. Slightly cooler temperatures return next week which should keep heat indices mostly below 105 degrees. 2. Greater than normal coverage of mainly diurnal showers and thunderstorms Sunday. A few severe storms again may occur Sunday, with damaging winds likely to be the main hazard. Mainly diurnal shower and thunderstorm chances linger through Tuesday, before a cold front brings potentially more severe weather on Wednesday.

DISCUSSION

Key message 1: Hot and humid conditions with heat index values ranging from 100 to 106 degrees again Sunday afternoon. Slightly cooler temperatures return next week which should keep heat indices mostly below 105 degrees.

Better convective coverage and associated cloud debris, along with lower thickness values, should allow for slightly cooler temperatures this weekend ranging from the low to mid 90s outside the mountains. However, dewpts will likely remain higher, ranging from the low to mid 70s. This will allow hot and humid conditions to linger thru the weekend with triple digit heat indices expected each afternoon outside of the mtns. Isolated locations could briefly see values of 105 though temperatures will be a tad cooler owing to more cloud cover, and mixing in most locations is expected to limit the extent of such values. Some consideration to a Heat Advisory will be given overnight, though forecast is leaning toward not needing one. Individuals should prepare for elevated heat thru the weekend. Stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

Key message 2: Greater than normal coverage of mainly diurnal showers and thunderstorms Sunday. A few severe storms again may occur Sunday, with damaging winds likely to be the main hazard. Mainly diurnal shower and thunderstorm chances linger through Tuesday, before a cold front brings potentially more severe weather on Wednesday.

An upper trof will dig into the Great Lakes region and the north- eastern CONUS thru Sunday as a cold front lays over the Carolinas from the north. Increased moisture advection ahead of the front and increasing low-level convergence will support above-normal convective coverage. With sfc-based CAPE likely reaching 2000 to 3000 J/kg during peak heating and deep layer shear increasing to 15 to 25 kts, convection could grow upscale into loosely organized clusters along outflow boundaries. Steep low-level lapse rates and high precip water values will create a threat for strong/damaging downbursts from individual cells. SPC Marginal Risk for most of the CWA again Sunday seems warranted; smaller area of Slight Risk in our east signifies the area with the best deep layer shear, which is also reasonable.

Diurnal convective chances linger thru Monday but confidence on the severe threat remains lower at this time. We should see a brief lull in coverage on Tuesday before a cold front brings better coverage back on Wednesday. Strong to severe storms will likely be possible on Wednesday, but confidence w.r.t. timing and extent this far out remains low.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Hard to be confident SHRA/TSRA won't redevelop near really any site for the remainder of the evening, excepting KAVL and KHKY since they were clearly worked over by storms prior to 00z. Lingering outflow boundaries could lead to at least isolated redevelopment, so VCSH is included at all the other terminals. Outflows also may lead to wind shifts this evening but in general sites should see mainly light, mainly SW winds (except NW at KAVL). The +RA at KAVL makes daybreak fog considerably more likely, so TEMPO'd in IFR for now. Otherwise, the daybreak concern is that low stratus could form over the lower Piedmont, but this is uncertain enough only to put FEW-SCT clouds at IFR level near daybreak for now. Diurnal cumulus may form at MVFR to low VFR level in the morning, before lifting. Similar coverage of showers/storms expected Sunday afternoon, and all sites get a PROB30 for diurnal SHRA/TSRA.

Outlook: Good coverage of afternoon/evening SHRA/TSRA continues thru Monday with less coverage expected on Tuesday before increasing again on Wednesday. Low stratus and/or fog will be possible each morning, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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