textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Heat Advisory issued for Union County NC.

KEY MESSAGES

1. Hot and humid conditions linger through Sunday with heat index values ranging from 100 to 105 degrees each afternoon. Slightly cooler temperatures return next week which should keep heat indices mostly below 105 degrees. 2. Coverage of mainly diurnal showers and thunderstorms increases through Sunday. A few storms could become severe both days with damaging winds the main hazard. Mainly diurnal shower and thunderstorm chances linger through Monday with a brief lull in activity on Tuesday before a cold front brings the potential for another round of severe weather on Wednesday.

DISCUSSION

Key message 1: Hot and humid conditions linger through Sunday with heat index values ranging from 100 to 105 degrees each 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, will allow for slightly cooler temperatures this weekend ranging from the low to mid 90s. However, dewpoints will be more elevated, ranging from the low to mid 70s. This will allow hot and humid conditions to linger through the weekend with triple digit heat indices expected each afternoon east of the mountains. Union County NC looks to be the only location with significant coverage of 105 heat index values today. Isolated locations elsewhere could briefly see 105. Therefore, have issued a Heat Advisory only for Union NC for now. Sunday will be a few degrees cooler which should keep any 105 heat index values limited to isolated locations.

Individuals should prepare for elevated heat through 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: Coverage of mainly diurnal showers and thunderstorms increases through Sunday. A few storms could become severe both days with damaging winds the main hazard. Mainly diurnal shower and thunderstorm chances linger through Monday with a brief lull in activity on Tuesday before a cold front brings the potential for another round of severe weather on Wednesday.

An upper trough will dig into the Great Lakes region and the northeastern CONUS through Sunday as a cold front approaches the area. Better moisture advection ahead of the front and increasing low-level convergence will support an uptick in coverage of convection both days. With sbCAPE reaching the 2,000-3,000 J/kg range during peak heating and deep layer shear increasing slightly to 15-25 kts each day, convection should become more organized. Steep low level lapse rates and high PW values will create a threat for damaging downbursts. Thus, the SPC Outlooks showing a Marginal and Slight risk across the GSP CWA for both days appear warranted.

Convective chances linger through Monday but confidence on the severe threat is low at this time. Should see a brief lull in coverage on Tuesday before a cold front brings better convective chances back Wednesday. Strong to severe storms are possible ahead of the front on Wednesday, but confidence on the severe threat this far out remains low.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Spotty convection near the TAF sites should dissipate by 08Z. Should then see VFR outside of mountain valley fog and low stratus. Chance at KAVL remains low, but high enough to keep the TEMPO for MVFR vsby and SCT IFR. Winds become light and variable early this morning. Lower VFR Cu develops during the day with a better chance of convection across the board. Have retained the PROB30s for all locations. SW winds pick up during the day with low end gusts, NNW at KAVL. Convection diminishes during the evening with VFR and light winds. Another round of mountain valley fog/stratus expected overnight.

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

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Heat Advisory from noon today to 8 PM EDT this evening for NCZ082. SC...None.