textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Severe Thunderstorm Watch was issued for western North Carolina and is in effect through 8 PM this evening.

KEY MESSAGES

1. Severe weather is expected this afternoon and evening ahead of a cold front with the main hazards being damaging winds and large hail, but there will also be an isolated tornado threat. Make sure you have multiple ways to receive warnings. 2. Heat and humidity peak today. A Heat Advisory remains in effect until 8 PM for portions of northeast Georgia and portions of the western South Carolina Upstate. Stay hydrated, limit time outdoors and spend as much time in air conditioning as possible. Never leave people or pets alone in a closed car. Look before you lock! 3. Less humid, drier, and cooler behind the front Wednesday through Friday. Even cooler conditions expected over the weekend into early next week with shower and thunderstorm chances returning.

DISCUSSION

Key message 1: Severe weather is expected this afternoon and evening ahead of a cold front with the main hazards being damaging winds and large hail, but there will also be an isolated tornado threat. Make sure you have multiple ways to receive warnings.

A Severe Thunderstorm Watch was issued and is in effect for western North Carolina until 8 PM this evening. The watch may need to be expanded southward later this afternoon or early this evening but this will depend on how storms evolve over the next several hours. The Day 1 Severe Weather Outlook continues to highlight a Slight Risk for much of the GSP CWA with damaging winds and large hail expected to be the main hazards, although there will also be an isolated tornado threat, especially across western North Carolina. A very favorable environment will be in place for late July with 30-40 kts of deep layer shear, 2,000-3,000+ J/kg of SBCAPE, and 2,000- 2,500 J/kg of MLCAPE, so any storms that develop will have the potential to become severe. Any discrete supercells that develop initially will have the potential to produce large hail but the hail threat should gradually lower as cells attempt to converge more into a line as storms push southward, per the 12Z CAMs. The tornado threat and damaging wind threat will linger throughout the duration of the event as both discrete supercells and storms eventually trying to organize into more of a line will keep these hazards around. With low-level 0-1 km shear ranging from mostly 10-20 kts this afternoon and early evening, per 12Z high-res model soundings, and with ~100-200 J/kg of 0-1 SRH expected, the tornado threat should remain low and isolated. Storms should clear the GSP CWA by around 9-10 PM.

Key message 2: Heat and humidity peak today. A Heat Advisory remains in effect until 8 PM for portions of northeast Georgia and portions of the western South Carolina Upstate. Stay hydrated, limit time outdoors and spend as much time in air conditioning as possible. Never leave people or pets alone in a closed car. Look before you lock!

Increased SW'ly flow will allow highs to end up around 4-8 degrees above normal this afternoon. Afternoon temperatures will climb into the lower to mid 90s east of the mountains and the upper 80s to lower 90s across the typically warmer mountain valleys. Heat indices east of the mountains will climb into the upper 90s to lower 100s. The Heat Advisory remains in effect through 8 PM for Elbert, Hart, Franklin, and Stephens counties in NE GA and for Greenwood, Abbeville, Anderson, and Oconee (non-mountains) counties in SC as these locations will see heat indices range from 105-108 degrees. Breezy W/SW winds ahead of the cold front will help provide a bit of relief from the heat and humidity this afternoon and early evening.

Key message 3: Less humid, drier, and cooler behind the front Wednesday through Friday. Even cooler conditions expected over the weekend into early next week with shower and thunderstorm chances returning.

The front will stall across the Deep South/Southeast during the rest of the workweek as surface high pressure builds into the region from the north. As a result, dry and cooler conditions will return Wednesday into Friday night. The front will slowly lift back northward this weekend into early next week allowing shower and thunderstorm chances to return. Even cooler temperatures are expected this weekend into Monday, with highs ending up just below normal to start August.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Strong to severe TSRA will develop ahead of a cold front this afternoon and evening. The main hazards are damaging wind gusts and large hail but there will also be a isolated and low- end tornado threat. Went with TEMPOs across the NC terminals as confidence is highest that these areas will see TSRA and associated restrictions. Maintained PROB30s across the SC terminals as confidence on TSRA and associated restrictions is lower. VFR conditions will prevail outside of TSRA this afternoon/evening but KAVL could see MVFR stratus develop around daybreak. Winds will generally be SW/W east of the mountains ahead of the front, turning WNW/NW behind the front overnight. Winds at KAVL will start out W/WNW ahead of the front, turning NW behind the front early this evening. Low-end gusts from 18-22 kts can be expected this afternoon and evening across the terminals, with higher gusts expected within any TSRA that tracks directly over a terminal. Gusts will gradually diminish by late this evening east of the mountains but will linger at KAVL through the 18Z TAF period. Dry conditions return behind the front late this evening and will linger through Wednesday.

Outlook: Dry and mostly VFR through Friday, with shower and thunderstorm chances and associated restrictions returning this weekend into early next week. Low stratus and/or fog will be possible each morning, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory until 8 PM EDT this evening for GAZ018-026-028- 029. NC...None. SC...Heat Advisory until 8 PM EDT this evening for SCZ010-011-019- 104.