textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Severe Thunderstorm Watch has been issued for the mountains and foothills of North Carolinas and northeast Georgia through 10 PM this evening.

The aviation forecast was updated to for 18Z TAF issuance.

KEY MESSAGES

1. Another Heat Advisory is in effect through this afternoon for the SC Upstate, northeast GA, and the Charlotte Metro. Hot and humid conditions persist most of this week, with little relief until this weekend. 2. Slight Risk for Severe Weather across western North Carolina this evening. More seasonally-typical diurnal convection continues for most of the week.

DISCUSSION

Key message 1: Another Heat Advisory is in effect through this afternoon for the SC Upstate, northeast GA, and the Charlotte Metro. Hot and humid conditions persist most of this week, with little relief until this weekend.

Hot and muggy conditions currently ongoing with temperatures getting well into the mid and upper 90s this afternoon with dewpoints in the upper 60s and low 70s. The Heat Advisory remains in effect for much of the Piedmont zones south of I-40. Starting to see dewpoints mix out as the boundary layer continues to deepen during peak heating, with a few locations still reach a Heat Index of 105 degrees. Decided to not do a Heat Advisory for Tuesday as temperatures and dewpoints will be slightly lower compared to the past few days.

Broad subtropical ridge will meander over the southern CONUS over the next few days before the center of the ridge retrogrades to the southwest CONUS and subtle height falls move in from the northwest over the CWA. A deep closed low will move across the central Canadian Providences and set up shop over the Hudson Bay and northern Quebec by Tuesday and Wednesday, which will send multiple rounds of shortwave troughs across the region starting around Thursday once this feature becomes more established. This will help bring small relief to the region later this week before an actual cold front makes its way into the region by this weekend into early next week, helping to potentially knock temperatures back down a few ticks below normal as a result.

Key message 2: Slight Risk for Severe Weather across western North Carolina this evening. More seasonally-typical diurnal convection continues for most of the week.

Convective initiation will be a little later than the typical start time during peak heating as a very weak frontal boundary advances across Tennessee this afternoon and moves into the region overnight tonight. The environment through the evening timeframe will be primed for severe weather potential ahead of the front with 20-25 kts of deep layer shear, 2500-3500 J/kg of SBCAPE, 1000+ J/kg DCAPE, and decent dry layer in the mid-levels to go along with steep level lapse rates. CAMs vary as far as how to handle the coverage for convection as most initiate scattered storms over east Tennessee and push across the border over the North Carolina mountains some time after 21Z. With just enough shear, some of the convection can become loosely organized and would be the mostly likely culprit for damaging wind gusts. The question will be how far east can this activity be maintained once it slips off the terrain into the Piedmont zones later in the evening, likely after 8 pm. In this case, the environment will lose some of its steam, but some of the CAMs are killing the activity a little sooner than we should anticipate as the dewpoints are mixing out more than what's actually happening in real time. The main area of concerns will be across the North Carolina mountains, foothills, and Piedmont (mainly west of I-77) from 4pm-8pm. Still can't rule out severe weather across northeast Georgia and Upstate South Carolina after 6pm, but the conditional threat is lower as coverage will be more isolated in these regions.

After today, the atmosphere becomes more suppressed as the cold front shifts south of the area and any feature that can provide forcing for ascent will be absent Tuesday and Wednesday, leading to mostly just some ridgetop convection across the mountains. Conditions become more favorable for an uptick in convection by Thursday into the weekend with shortwave troughs traversing across the southeastern CONUS, but specific details are in question this far out.

AVIATION /18Z MONDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions will prevail outside of showers and thunderstorms later this afternoon and evening, mainly for KCLT/KHKY/KAVL. Kept the PROB30 for TSRA and associated restrictions for these terminals, ahead of a cold front as confidence wasn't high enough for a TEMPO at this time. WNW to WSW winds are expected through the remainder of this afternoon and evening before turning out of the northwest on Tuesday once the cold front pushes across the area by around 12Z or so. Can't rule out some level of restrictions along the Tennessee/North Carolina border with MVFR/IFR cloud cover. Depending on the extent of the cloud cover, mountain valleys that escape the cloud cover overnight could induce some form of mountain valley fog/low stratus, which may impact KAVL around daybreak Tuesday. Not expecting showers or thunderstorms on Tuesday, with only some daytime cu and high clouds.

Outlook: More isolated coverage of showers and thunderstorms will be possible Tuesday and Wednesday, mainly over the mountains. Better chances for showers and thunderstorms Thursday into the upcoming weekend. Low stratus and fog will be possible each morning, especially in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory until 8 PM EDT this evening for GAZ018-026-028- 029. NC...Heat Advisory until 8 PM EDT this evening for NCZ070>072-082. SC...Heat Advisory until 8 PM EDT this evening for SCZ008>014-019- 104>109.