textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 12Z TAFs.

KEY MESSAGES

1. Hot and humid conditions remain in place, mainly east of the mountains through Saturday before cooler and less humid conditions return Sunday into early next week. Those with outdoor plans should stay hydrated and take frequent breaks in air- conditioned or shaded areas. Never leave children or pets in unattended vehicles. 2. Diurnal Convection becomes mostly confined to western North Carolina the rest of the workweek before a cold front potentially brings convective chances back to all areas this weekend. A few severe storms are possible during peak heating each day, with the main hazard being damaging wind gusts. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans.

DISCUSSION

Key message 1: Hot and humid conditions remain in place, mainly east of the mountains through Saturday before cooler and less humid conditions return Sunday into early next week. Those with outdoor plans should stay hydrated and take frequent breaks in air- conditioned or shaded areas. Never leave children or pets in unattended vehicles.

Bermuda High lingers over the western Atlantic through Saturday keeping hot and humid conditions around, mainly east of the mountains. Temperatures will end up around 4-7 degrees above normal area-wide through Saturday. Highs will rebound into the lower to mid 90s each afternoon east of the mountains, with heat indices ranging from the mid 90s to lower 100s. Most locations should remain below Heat Advisory criteria (<105 degrees) so no Heat Advisories are anticipated at this time. A cold front will track across the forecast area late Saturday, pushing south and east of the GSP CWA by daybreak Sunday. This departing front combined with the Bermuda High retreating will allow cooler and less humid conditions to return Sunday into early next week. Temperatures expected drop to near normal to just above normal area-wide. Highs east of the mountains should only reach into the upper 80s to lower 90s east of the mountains on Sunday and Monday.

Key message 2: Diurnal Convection becomes mostly confined to western North Carolina the rest of the workweek before a cold front potentially brings convective chances back to all areas this weekend. A few severe storms are possible during peak heating each day, with the main hazard being damaging wind gusts. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans.

Upper ridge centered in the western Atlantic near Florida will build northward into the Carolinas through tomorrow. This will help shunt most of the diurnal convection into western North Carolina today and tomorrow. Cannot entirely rule out some convection making it as far south as I-85, especially today, but confidence is low. The upper ridge then gets shunted southward a bit by weak upper troughing tracking over the Carolinas on Thursday. Embedded shortwaves within the trough could lead to better convective chances across mainly western North Carolina and especially along the NC/TN border on Thursday. Some activity could spill east of the mountains on Thursday but confidence is low, especially since the longer range CAMs currently only go out through 12Z Thursday. Hopefully once the 06Z CAMs trickle in later this morning, we will get a better picture of where convection will be focused on Thursday. Upper flow turns more zonal Friday into Saturday ahead of an approaching cold front. Convection should still be mainly confined to western North Carolina again on Friday before chances return for all areas over the weekend ahead of and along the front. Convection may linger behind the front on Monday but confidence is low at this time with this being towards the end of the forecast period. With deep layer shear expected to range from 15-20 kts and at least 1,500-2,500 J/kg of SBCAPE developing during peat heating today and tomorrow, a few strong to severe storms will be possible. Thus, the Marginal Risks for both Day 1 (today) and Day 2 (tomorrow) appear warranted. Any severe storms that develop will be capable of producing damaging wind gusts. Confidence on the severe threat Thursday onward is low at this time (despite 15-20 kts of deep layer shear remaining in place) as global model guidance sources, along with the NBM, generally depict lower instability during peak heating Thursday into early next week.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Mostly dry and mostly VFR through the 12Z TAF period outside of morning fog/stratus and afternoon/evening TSRA. Any fog/stratus that developed overnight will lift around or shortly after sunrise. Another round of TSRA is expected this afternoon, mainly at KHKY and KAVL, so maintained TEMPOs at these terminals. Maintained PROB30s at KGSP, KGMU, and KCLT for TSRA as confidence is lower on whether activity will make it that far south/east. KAND should remain dry through the period. Winds will be SW east of the mountains and NW at KAVL today. Wind speeds should remain fairly light at KAVL but will range from 5-10 kts east of the mountains. Winds will once again go calm to light and VRB late this evening into tonight. Mountain valley fog and low stratus should develop again overnight into daybreak Wednesday, with KHKY possibly seeing fog develop as well.

Outlook: The North Carolina terminals will have the best potential to see TSRA chances return each afternoon and evening Wednesday through Friday. TSRA chances return for all terminals this weekend. 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.