textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion.

KEY MESSAGES

1. Mainly diurnal convection into the weekend. 2. Hot and humid conditions develop today and continue into the weekend.

DISCUSSION

Key message 1: Mainly diurnal convection into the weekend.

Mountain valley fog, and patchy fog elsewhere, dissipates after daybreak leaving mostly sunny skies. An upper ridge slowly builds into the area today with a shortwave dropping down the east side of the ridge across the mountains and northern tier. The air mass will be very unstable and the wave should help initiate convection over the mountains and I-40 corridor. Outside of the mountains, high LFC's and a lack of forcing will limit initiation and actually help dissipate convection as it moves out of the mountains, the I-40 corridor being the exception. Shear is light but high dCAPE and sfc delta theta-e values will lead to a severe downburst threat for storms that become strong enough. The heavy rain threat is limited due to the overall drier airmass.

The upper ridge reasserts itself on Friday creating even higher LFC's. However, a shortwave barrels into the ridge and an old MCS boundary moves into the mountains during the afternoon. CAM guidance shows convection initiating along this boundary with good coverage over the mountains. Even with the poor conditions outside of the mountains, forcing will be enough to overcome that over the NC foothills and Piedmont bringing scattered late afternoon and early evening convection there. The forcing weakens to the west with only an isolated chance over the western Upstate and NE GA. The atmosphere is again very unstable with light shear. High dCAPE and sfc delta theta-e values continue as well. Severe storm chances will be better given the semi-organized nature of the convection. This has prompted SPC to introduce a Slight chance of severe over the NC mountains, foothills, and I-40 corridor with a Marginal chance south of there to the I-85 corridor. The semi-organization will lead to a better chance of locally heavy rainfall, especially over the mountains.

Convective chances diminish on Saturday with warmer mid-level temps limiting instability and lapse rates.

A series of shortwaves knock down the ridge and cross the area bringing zonal flow early next week and a trough by mid week. This brings weak frontal systems into the area and increasing chances of convection.

Key message 2: Hot and humid conditions develop today and continue into the weekend.

The upper ridge building over the area will lead to increasing heat into the weekend. Highs in the lower 90s will be common outside of the mountains today with mid 90s on Friday. Even the warmer mountain valleys will see highs around 90 on Friday. Highs drop a few degrees for the weekend, but lower 90s will again be common outside of the mountains. Confidence is increasing on these hot temps; however, confidence remains low on the dewpoints which will be what determines the resultant heat index. Right now, we have the heat index approaching 100 south of I-85 today, but they may very well remain below 100 if dewpoints mix out more than expected. Friday is the hottest day with the potential for for heat index values to eclipse 100 over the I-77 and I-85 corridors. Right now, it appears the heat index will be less than 105, but if temps or dewpoints end up a little higher, than a Heat Advisory would be needed. Heat index values will be near 100 again on Saturday and Sunday with the slightly cooler temps.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Mountain valley fog hasn't reached KAVL and may not before dissipating. The same with lake fog at KAND. KHKY has VLIFR fog which should dissipate before 14Z. Otherwise, low VFR stratocu lifts to high based Cu by afternoon. Guidance shows diurnal convection should be limited to the mountains and foothills, so PROB30s at KAVL and KHKY. Mountain valley fog expected again overnight. Light SW or light and variable wind this morning picks up from the SW, N at KAVL, during the day, going back light overnight.

Outlook: Diurnal convection and associated restrictions are expected into early next week. Mtn valley fog and low stratus will be possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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