textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Precip chances have been increased to 20-30% across much of the western quarter of the area for Sunday and Monday afternoon/evening.

KEY MESSAGES

1. A summer-like pattern will gradually evolve through early next week, with hot/above-normal temperatures and steadily increasing moisture resulting in slowly increasing chances for diurnal convection. 2. Mainly diurnal showers and thunderstorms are expected Tuesday and Wednesday before a cold front brings better rain chances Thursday into Friday. Well above normal temperatures stick around ahead of the front before cooler and near normal temperatures return behind the front on Friday.

DISCUSSION

Key message 1: A summer-like pattern will gradually evolve through early next week, with hot/above-normal temperatures and steadily increasing moisture resulting in slowly increasing chances for diurnal convection.

Heights will rise along the East Coast and across the western Atlantic through the weekend, supporting establishment of a summer-like Bermuda high pattern by the end of the weekend. As a result, after another relatively cool night under strong radiational cooling conditions tonight, temperatures will warm quite quickly over the weekend, with Saturday highs forecast at around 5 degrees above climo...further warming to almost 10 degrees above normal Sunday/Monday. Low level moisture will also increase, albeit slower than the heat. Nevertheless, enough moisture may be in place by Sunday afternoon to support development of isolated, diurnal deep convection in western areas, primarily across the mountains, with another round of isolated activity possible Monday afternoon.

Forecast soundings suggest a remnant elevated mixed layer will be in place across the Southeast...as mid-level lapse rates of 7.5-8 C/km are forecast during the Sunday/Monday time frame. Therefore, low level moisture will not need to be too rich to yield significant instability, and around 1500 J/kg of sbCAPE appears likely both afternoons. Upper flow and therefore shear parameters are forecast to be rather weak, but a few strong pulse-type updrafts are possible each afternoon.

Key message 2: Mainly diurnal showers and thunderstorms are expected Tuesday and Wednesday before a cold front brings better rain chances Thursday into Friday. Well above normal temperatures stick around ahead of the front before cooler and near normal temperatures return behind the front on Friday.

Upper ridging remains centered offshore the Southeast coast while gradually breaking down as an upper trough approaches out of the west Tuesday through Thursday. The trough should track over the forecast area Thursday, dragging a surface cold front across the region with it, before pushing east Friday. Mainly diurnal convection is expected ahead of the front Tuesday into Wednesday before better rain chances return ahead of the front on Thursday. Shower and thunderstorm activity appears to remain confined to the mountains on Tuesday, possibly spreading east of the mountains on Wednesday as the front inches closer. Global models show the potential for convection to linger through Friday but this will depend on the speed of the cold front. For now, NBM PoPs look appropriate through the period. Unfortunately, with only light rainfall amounts expected ahead of and along the front, not expecting much if any relief from the ongoing drought. Well above normal temperatures will linger across the region ahead of the front before cooler and near normal temperatures return behind the front on Friday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Moisture will very slowly increase through this forecast period, but the air mass will nevertheless remain relatively dry, resulting in continued VFR/mostly SKC conditions through bat least Saturday morning. SSW winds of 4-7 kts will develop by mid-afternoon, becoming light/variable or calm by late evening. SW winds will increase again to 5-8 kts by late Sat morning.

Outlook: Mostly VFR conditions are expected to continue into early next week, although the potential for mainly mountain valley morning fog will steadily increase. Isolated diurnal convection is possible early in the week, primarily across the mountains, with chances steadily increasing while expanding into the lower elevations as the week progresses.

GSP WATCHES/WARNINGS/ADVISORIES

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