textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Shower and thunderstorm chances have increased slightly for the mountains over the weekend.

KEY MESSAGES

1. Afternoon/evening shower and thunderstorm chances return through the weekend, with isolated severe storms possible. 2. Elevated heat risk by mid-week, with triple digit heat indices possible across most locations east of the mountains.

DISCUSSION

Key message 1: Afternoon/evening shower and thunderstorm chances return through the weekend, with isolated severe storms possible.

Kicking off the weekend with a mostly zonal flow aloft and a shortwave passing through. Moisture advection from the south/southwest, helps to increase shower and thunderstorm activity chances through this evening. Guidance doesn't favor much in the way of activity as an environment with weak flow through the mid-levels and a well mixed boundary layer, isn't conducive for severe thunderstorms. However, modeled soundings show a stout inverted-V with 800-1000 J/kg of DCAPE, indicating that any storm that does emerge, could produce strong winds. A few pop-up showers or thunderstorms over the mountains and isolated locations east of the mountains are possible through the evening.

For the weekend, a similar pattern emerges, but with one caveat. A developing ridge across the central CONUS begins to build, leaving the southeast and portions of the Mid-Atlantic in the path of potential downstream convection. Depending on how quickly this ridge develops and where the axis sets up, will have a direct impact on what, if any, severe thunderstorms could occur. Current guidance has a series of shortwaves moving through the Carolinas through Sunday, enhancing the chances for showers and thunderstorms. The mountains have the highest chances (50-70%), with only a slight chance elsewhere. Either way, it's summertime. Expect a few storms to pop up, especially near the mountains.

Key message 2: Elevated heat risk by mid-week, with triple digit heat indices possible across most locations east of the mountains.

As the ridge out west continues to amplify and move eastward, the probability of triple digit heat indices increases. This stout area of high pressure builds in hot summer heat through the weekend and continues to rise into next week. At this time, guidance has a 70- 80% probability of temperatures east of the mountains reaching 95 degrees or higher from Wednesday onward. Given the increase in moisture resulting in elevated dewpoints, this raises concerns for multiple days of heat indices of 100+. The one caveat, especially for the weekend, is any location that has a shower or thunderstorm could cool isolated areas. But, regardless, the signals are there in the guidance for a multi-day heat event, leading up to the 4th of July weekend. For this, it's important to plan for staying cool. Those who are outdoors should hydrate frequently and take breaks if working outside.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR conditions prevail through the TAF period. A few scattered showers and TSRA from now through 00z. KAVL is more likely to have a TSRA but confidence still remains low, so a PROB30 remains. Given the RA through KCLT earlier, a PROB30 should suffice for now as confidence is also low. There could be a brief period through 23z of low-end gusts of 15-20kts at KCLT as well. Otherwise, VCTS elsewhere and 5-10kt winds out of the SW. Overnight, a few terminals may become VRB before picking back up from the SW Saturday morning.

Outlook: Afternoon/evening shower and thunderstorm chances and associated restrictions continue through the weekend. Early morning fog/low stratus is possible each day, especially in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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