textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion has been updated for the 12Z TAFs.

KEY MESSAGES

1. Temperatures warm closer to normal today, with afternoon showers and thunderstorms confined to far western areas. 2. Hot conditions will return to the area Thursday and continue into the weekend. Heat index values may return into the 100 to 105 degree range across the Piedmont Friday through Sunday. A cold front will approach from the north and bring higher rain chances over the weekend, and slightly cooler temperatures early next week.

DISCUSSION

Key message 1: Temperatures warm closer to normal today, with afternoon showers and thunderstorms confined to far western areas.

Weak inverted surface ridging will persist over the area today, as a ridge aloft builds more strongly over the Mid-Atlantic and the Carolinas. Relatively dry air associated with the surface ridge will remain nosed into the area today, resulting in a gradient of diurnal instability, such that moisture/buoyancy sufficient for deep convection is forecast to be confined to the western fringe of the CWA, and afternoon PoPs (mostly 20-40%) will be confined to these areas. Considerably less cloud cover and the loss of ENE flow will result in temperatures warming to normal across much of the area today.

Key message 2: Hot conditions will return to the area Thursday and continue into the weekend. Heat index values may return into the 100 to 105 degree range across the Piedmont Friday through Sunday. A cold front will approach from the north and bring higher rain chances over the weekend, and slightly cooler temperatures early next week.

An upper ridge axis will persist across the region through week's end, albeit steadily weakening with time, as a series of height falls overspread the northeast quadrant of the country. As heights rise and the air mass continues to modify, a return to hot/above normal temperatures begins Thursday and persists through at least Friday. Maximum Heat Index values are likely to exceed 100 across portions of the Piedmont, and Heat Advisory conditions are possible both afternoon, although confidence is low at this juncture. Diurnal convection is expected to be largely confined to the mountains Thu/Fri afternoon, where instability may be robust enough to allow for a few pulse severe storms.

Height falls are forecast to carve out a long wave trough over the East during the weekend, which will moderate temps back to around normal while also enhancing diurnal convective chances, especially on Saturday...when likely mountain PoPs w/ solid chances elsewhere are forecast. More typical diurnal convective chances return early next week, although it's possible that another area of height falls/weak frontal zone could again enhance chances circa Tuesday.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: LIFR fog/low stratus is widespread in the mountain valleys this morning, including KAVL. KAVL should improve to VFR by 14Z. VFR is forecast to persist at all other TAF sites through this forecast period. Any diurnal convection is forecast to remain west of the terminals this afternoon/evening. Fog/low stratus is likely to redevelop in the mountain valleys tonight, and IFR visby is introduced at KAVL beginning at 08Z. Other than a brief period of light SW winds in the late afternoon/early evening, winds will be calm or light/vrbl through the period.

Outlook: Diurnal convective coverage is expected to increase somewhat Thursday, but should remain confined to the mountains. Typical mid-July coverage of diurnal convection is expected to return Friday and continue thru the weekend. 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.