textproduct: Greenville-Spartanburg

SYNOPSIS

High pressure over the area through tonight will result in mostly sunny skies and relatively low humidity. Seasonably hot and humid weather returns Thursday with numerous showers and storms each afternoon and evening through the weekend.

NEAR TERM /THROUGH TONIGHT/

As of 617 AM Wednesday: A smattering of fog observations have been noted across the area this morning, especially across the usual mountain valleys. Fog will continue for another hour or two before quickly mixing out. Otherwise, a large scale trough over New England will continue to lift northeast into the Canadian Maritimes today. Early morning surface observations and low-level ThetaE fields depicts an attendant cold front draped across the area with the boundary oozing southeast through the pre-dawn hours. Guidance is in generally good agreement that the boundary will slide just south of the area today with drier post-frontal air filtering across much of the region. Heights will also rise in the wake of the departing trough with increasing subsidence. The result will be a dry forecast for much of the area. The exception will be the potential for an isolated shower or thunderstorm across far southern and eastern reaches of the area in the vicinity of the stalled frontal boundary. Continued influence of surface high pressure will promote fairly efficient radiational cooling tonight, depending on influences from cloud cover, with seasonal lows falling into the low to upper 60s.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/

As of 130 AM Wed, key messages:

1. Subtropical air spreads back over the area Thursday as warm front activates and lifts northward. This should permit a return of scattered showers/storms, with isolated damaging wind and torrential rainfall both possible.

2. Continued moisture return should result in greater coverage of showers/storms Friday. Damaging wind threat may decrease somewhat, but heavy rain and localized flash flood threats remain similar if not increase.

3. Temperatures will be near normal with high humidity both days.

Upper low and surrounding shortwave will be centered over eastern TX/OK Thursday, drifting slowly northeast into MO Friday. Upper ridging associated with Bermuda High will persist over the Carolinas and Georgia. Warm front will shift north across the CWA, and temps will be slightly warmer than Wed, a tad above normal. The front should low-level dry air and make deep convection plausible once again, particularly over the southern half of the area and the south-facing Blue Ridge Escarpment, where PoPs rise to 50-60%. Forcing mainly will be diurnal instability aided by weak WAA near the surface. The speed of moisture return may be critical for severe weather potential. NAM, GDPS and the longer range CAMs maintain fairly dry profiles aloft, perhaps keeping convection a bit more sparse but also making for enough DCAPE and sfc-midlevel theta-e lapses to expect at least isolated damaging microbursts might develop, particularly given deep layer shear of 15 kt or less. GFS and ECMWF depict deeper saturation which would suggest better coverage and perhaps slightly less potential for damaging wind. As southerly flow persists Thu night and a few hundred joules of MUCAPE remain, isolated or widely scattered storms may redevelop much of the night, so PoPs decline slowly.

The moisture return will continue Friday; shortwave still is likely to be too far west of the area to have much of an effect. Enhanced diurnal pattern once again. LCLs look a little lower, with PWATs similar if not slightly higher. Accordingly PoPs tick 10-20% higher, ending up likely across the whole CWA and categorical over the SW NC mountains and near the Escarpment. Shear won't be any stronger. Wet microbursts producing locally heavy rain and in some cases marginally severe winds will be the main concern. Flash flood threat may be a little higher particularly where heavy rain develops for the second day in a row. PoPs decline slowly again Friday evening.

LONG TERM /SATURDAY THROUGH TUESDAY/

As of 200 AM Wed, key messages:

1. No significant change in the weather pattern through at least Saturday, and probably Sunday. PoPs mostly on a diurnal curve. Temps fall slightly below normal mostly as a result of increased cloud cover, but elevated dewpoints persist.

2. A weak shortwave may shift over the area Sunday or Monday, potentially further enhancing shower/storm coverage those days, but also possibly introducing drier air aloft by Tuesday.

3. Typical June threats of wet microbursts producing localized heavy rainfall and perhaps a few instances of damaging wind each day.

Since this time yesterday, models have come into a little better agreement that the upper low will rejoin the westerlies by around Saturday as an open shortwave, and slowly will progress toward our CWA thru Sunday. Saturday looks similar to Friday in that synoptic forcing will be weak, but southerly flow will continue to moisten the column and PWATs thus are likely to be slightly higher. Above-climo PoPs still are forecast, likely to categorical range. There does remain some spread in the position of the shortwave; faster solutions develop slightly more shear but flow overall will remain weak and generally unidirectional even if so. Regardless, heavy rain and isolated minor flooding are probably the main threats, but it's hard to rule out at least isolated severe winds given the expected coverage and the seasonably high instability. Cloud cover looks enough to bring temps down a degree or two from Friday.

The trough is even more likely to be to our west Sunday. Although it is not likely to provide an appreciable uptick in shear or necessarily even to focus convective development, its presence helps make up for the usual decline in confidence as range increases, so PoPs end up similar to Saturday with temps slightly cooler once again. The enhanced diurnal pattern is likely to continue Monday and Tuesday, but those days we will be increasingly likely to see the shortwave turn winds westerly aloft, which leads NBM temps warmer Monday with more members depicting downslope winds, and then PoPs finally trending lower Tuesday as drier air is likely to have reached the upper levels over our area.

AVIATION /10Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: A few isolated areas of patchy of and low stratus have been noted on area observations and satellite this morning. Any lingering restrictions until ~12z should quickly dissipate shortly thereafter, if not before the start of the TAF period. Otherwise, VFR conditions will prevail through the TAF period with light and variable winds shifting from out of the north to gradually out of the south. Variations in direction will be possible through the day given the weak magnitude of the winds and a building surface high pressure across the region.

Outlook: Mainly diurnal thunderstorms return Thursday and will persist each afternoon/evening into the weekend. There will be potential for late night and early morning fog and low stratus restrictions each day.

GSP WATCHES/WARNINGS/ADVISORIES

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