textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Rain chances trending higher Thursday into Saturday, with rainfall amounts trending higher, especially on Thursday.

Trending cooler for Friday.

KEY MESSAGES

1. A summer-like pattern will be in place through mid-week, with above normal temperatures, increasing humidity, and spotty diurnal convection expected. 2. A cold front brings better rain chances mid to late week but with rainfall amounts expected to remain light, any drought relief will be limited. Well above normal highs linger through Thursday before cold air damming leads to the return of below normal highs Friday into Saturday.

DISCUSSION

Key message 1: A summer-like pattern will be in place through mid-week, with above normal temperatures, increasing humidity, and spotty diurnal convection expected.

A Bermuda high will persist and gradually expand/intensify across the western Atlantic through mid-week as an upper ridge builds strongly along the East Coast. Resultant low-level trajectories off the eastern Gulf will support steadily increasing moisture across our forecast area through Sunday, with surface dewpoints in the upper 50s/lower 60s expected during the afternoon. Meanwhile, an expansive elevated mixed layer will continue to cover much of the eastern half of the country through Sunday, with mid-level lapse rates of around 8 C/km forecast across the Southeast. That being the case, strong insolation (max temps 6-9 degrees above climo; about 5 degrees warmer than today) is resulting in forecast soundings depicting surface-based CAPE of around 2000 J/kg despite the somewhat modest dewpoints Sunday afternoon. On the other hand, there is a decent capping inversion at the top of the relatively moist boundary layer. In light of any organized areas of upward vertical motion, initiation of deep convection will therefore be a bit of a tall order across the CWA Sunday afternoon, but will be most likely across the far west. Additionally, convection could initiate upstream across central GA...where the cap is forecast to be weaker...and wander into the western zones by late afternoon/early evening. 20-30 PoPs will be carried across ~the western third of the area during this time frame. Wind shear will be practically non- existent, but a few strong updrafts pulses can't be ruled out given the degree of buoyancy.

Mid-level lapse rates will begin to steadily modify Sunday night into Monday, as temps warm aloft in association with the building upper ridge. Nevertheless, with dewpoints continuing to steadily increase, forecast soundings suggest sufficient instability to warrant small PoPs across the far western mountains during the afternoon. As time progresses toward mid-week, low level trajectories are expected to become more oriented off the western Atlantic as the Bermuda high expands...such that lower theta-E air originating from the subsident region within the anticyclone will advect into the area...lowering surface dewpoints/increasing stability as the mid-levels continue to warm. Diurnal convection therefore is not expected Tuesday. Temperatures will otherwise remain steady at 6-9 degrees above normal through Tue night.

Key message 2: A cold front brings better rain chances mid to late week but with rainfall amounts expected to remain light, any drought relief will be limited. Well above normal highs linger through Thursday before cold air damming leads to the return of below normal highs Friday into Saturday.

The bermuda high remains in control of the pattern on Wednesday ahead of an approaching cold front. This will act to keep hot and well above normal temperatures around, especially east of the mountains, as well as keeping around diurnal shower and thunderstorm activity. The front tracks across the forecast area Thursday before stalling over the Deep South and coastal Carolinas Friday into Saturday, bringing better coverage of showers and thunderstorms. Although NBM PoPs and QPF are trending a bit higher compared to the previous forecast, rainfall amounts still look to remain below an inch across most locations Thursday through Saturday. A few lucky locations could see rainfall amounts greater than 1" but this should be localized. Will continue to monitor QPF trends closely in the coming days but for now it appears there will be limited relief from the drought with this front. Cold air damming develops behind the front as high pressure builds in from the north Thursday night into Friday, with the wedge expected to linger through at least Saturday. CAD will act to limit the severe potential as well as allow for the return of below normal high temperatures. The NBM has trended much lower compared to this time yesterday regarding Friday's highs so expect this trend to continue in the next several forecast cycles, with this trend also possible for Saturday as the wedge remains locked in place.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

At KCLT and elsewhere: VFR is forecast to persist across the Terminal Forecast Area through the period, with mainly increasing high clouds anticipated through tonight. Having said that, guidance sources are signaling some potential for low clouds to drift into the Piedmont from the south and southwest toward daybreak Sunday. Confidence in this remains very low at this juncture, and low clouds will not be reflected in the forecast. SW winds of 6-10 kts this afternoon will become light this evening...increasing from the SW at 4-7 kts by early Sunday afternoon.

Outlook: VFR conditions expected to persist through mid-week, except in mountain valleys, where there will be some potential for morning fog/low stratus, especially early in the week. Isolated diurnal convection is possible Sunday and Monday afternoons, primarily across the mountains, and perhaps near KAND. An active cold front may bring restrictions associated with convective precip by late week.

GSP WATCHES/WARNINGS/ADVISORIES

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