textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 00Z TAFs. Otherwise, no significant changes.

KEY MESSAGES

1. Afternoon/evening shower and thunderstorm chances return tomorrow and continue through the weekend, with isolated severe storms possible Saturday. 2. Hot weather is forecast to escalate during the new work week, with triple digit heat indices possible across most of our lower terrain by mid-week.

DISCUSSION

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

The air mass remains relatively dry for early summer across the forecast area this afternoon, resulting in weak-at-most instability and therefore little-to-no chance for diurnal convection. Seasonal temperatures are expected through Friday, with some fog/low stratus again expected to develop late tonight in the most favorable mountain valley locations. Low level S/SW flow will continue to become established over the region in response to upstream height falls, with moisture advection expected to ramp up late tonight into early Friday. This should allow for modest destabilization and diurnal convective development across the CWA Friday afternoon, with mostly 30-40 PoPs advertised.

Height falls/weak upper troughing are forecast to impact the East on Saturday, with an associated surface boundary expected to focus increased convective coverage during the afternoon. Saturday PoPs range from 50-70% across much of western NC, to 20-40% across the remainder of the CWA. Strong heating...max temps forecast to be a couple of degrees above climo...and elevated moisture is forecast to result in at least moderate instability. Wind fields will remain generally weak, but low level shear may prove adequate to promote some cell clustering along outflows. This along with better coverage and increased instability will promote the potential for a few isolated severe storms.

The flow aloft will become increasingly anticyclonic over the region late in the weekend, as heights rise strongly in association with a strengthening anticyclone centered over the lower Miss Valley. Nevertheless, forecast profiles again become favorable for deep convection Sunday afternoon, although coverage is expected to be less than on Saturday (mostly 30-40 PoPs) in light of the developing unfavorable upper air pattern. Temperatures will otherwise continue to climb under rising heights, with Sunday forecast maxes around 5 degrees above normal. This is expected to yield peak Heat Indices at or just above 100 across the southern fringe of the CWA.

Key message 2: Hot weather is forecast to escalate during the new work week, with triple digit heat indices possible across most of our lower terrain by mid-week.

An anticyclone will remain the most prominent feature impacting the Southeast and Mid-Atlantic during the new work week, resulting in increasingly hot conditions across our forecast area as the week progresses. Forecast temps begin the week around 5 degrees above normal...warming to almost 10 degrees above climo by Thursday...when some Piedmont locations could see ambient temperatures reach the century mark. Relatively dry air aloft and a subsident regime should promote some degree of surface dewpoint mixing during each afternoon...but maximum Heat Indices are forecast to reach around 100 across the Piedmont Wednesday. Next Thursday appears to be the most likely day for Heat Advisory criteria to be met...mainly across the Lakelands area as well as the I-77 corridor. Conditions will generally be unfavorable for deep convection, but we are now in the time of year in which it is difficult to not get at least a few afternoon showers to pop over the high terrain. PoPs are therefore primarily limited to the mountains each afternoon Monday-Thursday, and even those chances are capped at 20-30%.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: VFR conditions expected tonight, except for some mountain valley fog. Once again, it's expected to be in the valleys west and north of KAVL, but cannot be completely ruled out. S/SW winds will become calm or lgt/vrb this evening, then pick up again out of the SW again late Friday morning. As moisture increases out of the south late tonight thru Friday, there may be areas of VFR-level stratocu or mid clouds before daybreak, especially across the Upstate. Diurnal convection is expected to return across the area, mainly in the mountains and the piedmont roughly along and east of the Upstate TAF sites to KCLT. All sites will have a PROB30 for potential TSRA, except KHKY for now.

Outlook: Afternoon/evening shower and thunderstorm chances and associated restrictions continue through the weekend. Diurnal convective chances diminish a bit early in the new work week, as upper level high pressure strengthens over the region. Early morning fog/low stratus is possible each day, especially in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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