textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

PoPs have trended lower Monday thru Wednesday.

Updated the aviation discussion for the 06z TAFs.

KEY MESSAGES

1. Isolated to widely scattered showers and thunderstorms today, then greater coverage of storms across the area Sunday. A few storms may be severe on Sunday, with damaging wind gusts being the primary threat. 2. Hot and humid conditions continue through the weekend, followed by drier and slightly below-normal temperatures Monday and early next week.

DISCUSSION

Key message 1: Isolated to widely scattered showers and thunderstorms today, then greater coverage of storms across the area Sunday. A few storms may be severe on Sunday, with damaging wind gusts being the primary threat.

An area of relatively drier air will work in from the west, as the forecast area will be in between two shortwaves within a broad upper trough. At the sfc, a weak front will stall out along or just south of the CWFA border. Dewpts are expected to mix out slightly into the upper 60s across the Piedmont in the wake of this front, which will limit instability. Therefore, the convective potential today will be limited to mainly diurnal mountain-top-initiated activity. Cannot rule out a strong to severe storm with the strongest cells, as DCAPE should be fairly high, given mid-level dry air. Shear will be weak, leading to a pulse storm mode. The 00z CAMs are not impressed thru 00z, except for the usually hot HiRes-Window FV3, but do show an uptick in mainly showers forming near the stalled front, as it may reactivate ahead of another shortwave. Confidence remains low on how much typical diurnal convection will fire and what may be able to develop this evening.

A more active day is expected Sunday, as another shortwave tracks thru the broader longwave trough and brings more pronounced height falls across the region. The shortwave will be accompanied by a sfc cold front, which will push in from the west during peak heating and cross the CWFA thru the evening hours. An uptick in 0-6 km bulk shear of 25-30 kt along with better forcing could lead to a few severe storms. The storm mode looks to be a few linear multi-cell clusters tracking along/ahead of the front. So, damaging wind gusts will be the main threat. The NBM PoPs may be a little too low east of the mountains, but there is some potential that convection may struggle to cross the mountains. The new Day 2 Convective Outlook from SPC has our area in a Marginal Risk, which looks good. Convection should exit the area to the east by late evening.

Key message 2: Hot and humid conditions continue through the weekend, followed by drier and slightly below-normal temperatures Monday and early next week.

Despite a weak front pushing thru the area this morning from the north, temps will remain above normal today. Dewpts are expected to mix out into the upper 60s across most of the Piedmont, but with temps still in the mid 90s, heat indices will likely be in the upper 90s to around 103 across the Piedmont this aftn. It should be noted that the experimental HeatRisk is highlighting major heat impacts across most of the area along and southeast of I-85 today. This is likely due to it being early in the summer with temps a few deg above normal. Even though heat indices are expected to stay below advisory criteria, please be sure to take proper heat precautions. Dewpts and temperatures may creep upward slightly on Sunday. If convection manages to trend slightly slower, some areas may push Heat Advisory criteria along our far southern and eastern zones.

A nice reprieve from the heat should arrive Monday, as a cold front brings a noticeable drop in dewpts across the area along with temps down to near normal. The dry air may push far enough in to make for a basically dry day, although the NBM still has slight chc to low-end chc PoPs across the mainly the Piedmont Monday evening. An upper trough continues to dig across the Ohio Valley to the Southeast and helps shunt moisture to our south and brings slightly below normal temps for Tuesday. From there, the flow remains fairly flat, which should result in a slow warm up to slightly above normal temps by the end of the week. Guidance is not in great agreement on timing of next front to push in from the north late in the week. The latest NBM has the highest rain chances on Thursday, but the 00z GFS and ECMWF have pushed the higher chances back to Friday.

AVIATION /07Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Other than potential fog at KAVL between about 9-12z due to rainfall yesterday, VFR conditions expected thru the period. Only isolated to widely scattered convection expected today, mainly in the mountains. Chances are marginal at KAVL, but keep a PROB30 from 19-23z. Chances too low elsewhere. Convective Cu field still expected to form by early aftn, then dissipate after sunset. Winds will be light, mainly out of the SW this aftn, and otherwise quite VRB thru the period.

Outlook: Greater coverage of diurnal convection and associated restrictions expected on Sunday. Then relatively quiet thru midweek. Valley fog and low stratus is possible each morning, primarily in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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