textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 06Z TAFs.

KEY MESSAGES

1. Shower and thunderstorm chances linger through the weekend. Isolated severe storms capable of producing damaging wind gusts are possible this afternoon/evening. 2. Heat risk will increase through at least midweek, with heat indices potentially exceeding 100 degrees across much of the Piedmont and foothills.

DISCUSSION

Key message 1: Shower and thunderstorm chances linger through the weekend. Isolated severe storms capable of producing damaging wind gusts are possible this afternoon/evening.

Mostly zonal flow aloft with a surface boundary draped to the north will allow for a moist and unstable environment to get underway as a weak shortwave shifts across the CWFA during the daytime period. Dewpoints in the low 70s will lead to good destabilization (1500-2500 J/kg SBCAPE) with scattered to numerous showers and thunderstorms expected to the develop. A few storms are likely to become strong to severe as steep low-level lapse rates and very modest low-level shear will aid in the development of storm clustering capable of damaging winds. CAMs have been fixated on western NC, but this threat will extend into northeast GA and Upstate SC with less convective coverage expected compared to NC. Overall timing is expected between 2 PM and midnight tonight, with multiple rounds of severe weather being possible throughout that time period. The severe threat should wane after midnight with the loss of instability, but lingering showers and thunderstorms can't be ruled out during the overnight period. Afternoon highs are expected to be at or slightly above normal.

Another round of convection is possible on Sunday as a deepening upper/mid-level anticyclone forms over the lower/mid-MS Valley. This will place the area in the "Ring of Fire" with northwesterly flow aloft becoming established as convection moves downstream from the top of the ridge axis. Timing and locations being impacted have been variable via CAMs and deterministic models, but lingering convective debris and the potential for the atmosphere to be overturned from Saturday's convection should limit the overall severe threat. In this type of setup, the typical diurnal time line doesn't play a role for when potential decaying MCSs move across portions of the CWFA, but can determine the severity if a cluster of storms moves into the area during peak heating. Will be something to monitor, especially after today's expected severe threat. Afternoon highs will also be variable on Sunday as convective debris and daybreak stratus could keep temperatures from reaching the current forecasted max temperatures.

Key message 2: Heat risk will increase through at least midweek, with heat indices potentially exceeding 100 degrees across much of the Piedmont and foothills.

Deepening upper/mid-level anticyclone will set up shop over the lower/mid-MS Valley this weekend into early next week, while propagating eastward through mid-week. Most of the guidance places the closed upper ridge over the eastern CONUS by mid-week, which will allow afternoon highs to uptick into the mid 90s by Wednesday, with some locations possibly getting into the upper 90s. Drier air aloft and low-level subsidence should help dewpoints mix out during peak heating each afternoon, but may not be enough to forgo Heat products as the concern for multiple days of heat indices of 100+ degrees becomes realized by mid to late week. This synoptic setup will also help to suppress convective initiation as any afternoon/evening convection will likely remain over the higher terrain. Guidance keeps the ridge intact through at least D7, meaning the multi-day heat event could linger into the Independence Day Holiday weekend as there isn't a strong signal for relief from the heat.

Those with outdoor plans, including holiday and recreation, should prepare for several days of elevated heat risk. Stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Mostly VFR conditions expected through the forecast period. Lingering VFR cloud cover sticks around through the overnight period as light south to southwesterly winds continue. Mountain valley fog/low stratus is possible by daybreak, mainly over the Little TN Valley. Scattered showers and thunderstorms are likely this afternoon and evening and timed this out using a PROB30 at all TAF sites for TSRA and associated restrictions. Confidence is slightly higher for KAVL and placed a TEMPO mention to indicate the higher chances. Low-end gusts out of the south to southwest are expected during the afternoon at 15-20 kts. Guidance has hinted at possible overnight stratus with MVFR potential, but confidence is low at this time. However, put a SCT MVFR mention at KAVL to hint at this potential. There is also some indication of showers and thunderstorms continuing into the overnight period. Didn't make a TAF mention for it at this time, but something that will need to be monitored throughout the daytime period.

Outlook: Daily chances for showers and thunderstorms, as well as associated restrictions, will linger through early next week. Mountain valley fog/low stratus will possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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