textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 00Z TAFs.

KEY MESSAGES

1. Hot and humid conditions linger through the weekend 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 weekend. A few storms could become severe, especially over the weekend, with damaging winds being 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 the weekend 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 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. Due to slightly lower temperatures, the current forecast keeps heat indices just below Heat Advisory criteria (which starts at 105 degrees) through the weekend. Next week even cooler highs will develop, acting to keep heat indices mostly below advisory criteria.

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 weekend. A few storms could become severe, especially over the weekend, with damaging winds being 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 northeastern CONUS this weekend 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 convective this weekend. With 2,000-3,000+ J/kg of SBCAPE developing during peak heating and deep layer shear increasing slightly to 15-25 kts each day, convection should become more organized over the weekend. Thus, the SPC Day 2 Severe Weather Outlook showing a Marginal risk across the entire GSP CWA for Saturday and the Marginal to Slight risk across the GSP CWA for Sunday appears warranted. Any severe storms that develop will be capable of producing damaging wind gusts.

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 and the Day 6 Severe Weather outlook from SPC has areas along/near I-77 in a Slight risk. Confidence on the severe threat this far our remains low.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Scattered SHRA/TSRA lingers across mainly the SC Upstate this evening, with some isolated activity noted near KCLT. Activity will gradually wane through sunset, allowing dry conditions to return. Mountain valley fog and low stratus should develop across portions of the mountain valleys tonight into daybreak Saturday. Went have a TEMPO for MVFR cigs and SCT IFR stratus at KAVL from 09Z-12Z but confidence is low as the terminal did not see RA this afternoon/evening. Otherwise, dry and VFR outside of TSRA Saturday afternoon and evening. Have PROB30s across the terminals to account for TSRA and associated restrictions Saturday afternoon/evening. Winds will go calm to light and VRB this evening into tonight east of the mountains, although KCLT should see a light S/SW later this evening into tonight. Winds at KAVL should generally remain NW/WNW through the period but should go calm overnight into daybreak Saturday. Winds east of the mountains will pick up out of the SW/WSW Saturday morning with speeds gradually increasing. Some low-end gusts could develop Saturday afternoon and evening, especially at KCLT.

Outlook: Coverage of afternoon/evening SHRA/TSRA gradually increases this weekend with a few strong to severe storms possible each day during peak heating hours. Afternoon/evening SHRA/TSRA should linger through early next week but a brief lull in coverage may develop on Tuesday. Low stratus and/or fog will be possible each morning, mainly in the mountain valleys.

CLIMATE

RECORDS FOR 07-17

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 95 1980 72 1917 77 1887 54 1939 1891 KCLT 100 1986 74 1989 80 1881 62 2004 1887 1896 1903 1886 KGSP 103 1887 76 1930 76 1934 60 1886

GSP WATCHES/WARNINGS/ADVISORIES

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