textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes.

KEY MESSAGES

1. Hot and humid east of the mountains through Saturday before much cooler and possibly below normal highs for mid-July return Sunday into Tuesday as cold air damming develops behind a cold front. 2. Diurnal showers and thunderstorms will be mostly confined to western North Carolina again today before better coverage of diurnal activity returns Friday. A cold front brings even better shower and thunderstorm chances this weekend into Monday before drier conditions return Tuesday into Wednesday.

DISCUSSION

Key message 1: Hot and humid east of the mountains through Saturday before much cooler and possibly below normal highs for mid-July return Sunday into Tuesday as cold air damming develops behind a cold front.

Bermuda high keeps hot and humid conditions around east of the mountains through Saturday. Although highs east of the mountains will rebound into the low to mid 90s today and tomorrow, dewpoints should mix out enough each afternoon allowing heat indices to remain below Heat Advisory criteria (<105 degrees). Highs will be cooler Saturday as the Bermuda High gets nudged southward by a cold front approaching from the north. However, afternoon temps east of the mountains will still climb into the upper 80s to lower 90s, with heat indices ranging mostly from the lower to upper 90s.

A cold front will bring much needed relief from the heat starting Sunday. The front should push south of the GSP forecast area by daybreak Monday. Behind the front, cold air damming will gradually develop as surface high pressure centers itself over the Northeast. Cold air damming looks to be strongest on Monday and could linger through Tuesday. This will allow below normal highs to return late this weekend into early next week, with Monday potentially seeing highs drop down to 5-10 degrees below normal. Highs appear to mostly range from the lower to mid 80s east of the mountains each day.

Unfortunately the break from the summer heat will be brief, as highs east of the mountains on Wednesday and Thursday will climb back into the low to mid 90s as an upper ridge builds over the central and eastern US. By Thursday we should see highs return to around 5 degrees above normal for mid-July.

Key message 2: Diurnal showers and thunderstorms will be mostly confined to western North Carolina again today before better coverage of diurnal activity returns Friday. A cold front brings even better shower and thunderstorm chances this weekend into Monday before drier conditions return Tuesday into Wednesday.

Diurnal convection returns today, mainly across western North Carolina again. However, 00Z CAMs do show the potential for some isolated convection to develop across northeast Georgia and the South Carolina Upstate. The severe weather threat will remain very low today like we saw yesterday. However, a few strong, sub-severe storms are possible during peak heating hours. Convective coverage increases slightly on Friday and with CAMs showing the potential for more organized convection to develop, the severe threat will increase a bit compared to today. The main hazard with any severe storms that develop the next two days will be damaging wind gusts.

A cold front will approach out of the north Saturday into early Sunday before tracking across the forecast area late Sunday into early Monday morning. This front will bring even better coverage of showers and thunderstorms, especially Sunday into Monday. Confidence on any severe weather developing with this front remains low, especially Sunday into Monday with cold air damming expected to develop. With mainly diurnal convection likely to develop again Saturday (as the front remains well to the north), a low-end isolated severe threat will continue with damaging winds being the main hazard with any severe storms that manage to develop.

AVIATION /07Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Dry and VFR through most of the 06Z TAF period outside of the potential for morning mountain valley fog and stratus and scattered TSRA this afternoon/early evening. KAVL will have the potential to see LIFR cigs and IFR fog develop closer to daybreak so have a TEMPO from 09Z-12Z. The NC terminals will once again have the best potential to see TSRA develop this afternoon/early evening so went with PROB30s at KCLT, KAVL, and KHKY. Although 00Z high-res guidance shows the potential for a few isolated TSRA to develop across the SC terminals, confidence is too low on whether this activity would track directly over KGSP, KGMU, or KAND. Thus, maintained dry conditions at the SC terminals for now. Winds at KAVL will be mostly NW/WNW while east of the mountains will be mostly W/WSW through the period. Breezy winds will return again today, mainly east of the mountains, with gusts ranging from mostly 18-22 kts. Gusts will diminish around or just after 00Z Friday.

Outlook: Better coverage of SHRA/TSRA returns for all terminals Friday into Monday. Drier conditions should develop Tuesday into Wednesday. Low stratus and/or fog will be possible each morning in the mountain valleys and in locations that see appreciable rainfall the previous afternoon/evening.

GSP WATCHES/WARNINGS/ADVISORIES

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