Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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502 FXUS62 KGSP 251729 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 129 PM EDT Tue Jun 25 2024 .SYNOPSIS... High temperatures will peak on Wednesday ahead of a cold front. Shower and thunderstorm chances increase Wednesday into Thursday as the front moves across the area. Behind the front, afternoon shower and thunderstorm chances will persist through Saturday. Hot and humid conditions are expected on Sunday with numerous showers and thunderstorms possible as another cold front enters the area. Typical summer weather is expected behind the front to start the next work week. && .NEAR TERM /THROUGH TONIGHT/... 1000 AM Update...Low clouds are lingering across the nrn NC foothills and expect these to dissipate over the next couple hours as LCLs rise into drier air. Updated the sky grids to reflect this change, otherwise made little adj/s to the going fcst. Otherwise, sfc high pressure will continue to build in from the north and will remain over the western Carolinas and northeast Georgia through tonight leading to continued dry weather. Although humidity will remain low again today, with minimum RH values dropping down to 30%-35% across much of the area this afternoon, hot temperatures will return once again. Highs will climb into the low 90s in the mountain valleys and the low to mid 90s east of the mountains. Lows tonight will be warmer (and ~5-8 degrees above climo) thanks to 850 mb winds turning S/SW`ly. This will also allow humidity to increase again tonight east of the mountains. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 130 AM Tue: Shortwave crossing the Great Lakes Tue night will promote height falls Wed afternoon and evening over our region; sfc front should reach the Ohio River before sunset. With midlevel ridge to the west, we will mix up into dry air again for part of the day, although 850-700mb flow will become southerly in advance of the trough during the afternoon. Thus, despite diurnal instability model QPF response is low during the day, and PoPs appear warranted only over the mountains. Convection will develop ahead of the front in KY/TN but with the front itself not reaching the mountains until overnight, the convection is expected to ash out before it gets to our border. Under exceptionally high thicknesses, temps Wed may be the hottest of the year so far, with upper 90s across the Piedmont and low 90s for the mountain valleys. As noted however dewpoints will mix out enough that heat index should peak "only" around 100 in the lower Piedmont. Models differ as to how quickly the front settles through our area, and it becomes rather diffuse as it is. It looks mainly to serve as a source of weak convergence and promote moisture pooling, thus a focus for diurnal convection. Confidence remains best for mountain and northwest NC Piedmont PoPs during the day Thursday, 50 to 60% in those areas. The front should reach the southern half of the CWA by the end of the day and our southern zones still get at least 40% PoP. Shear will remain seasonably weak but lapse rates not strong enough through a deep layer to produce especially high CAPE, although a damaging microburst or two can`t be ruled out. Dewpoints don`t look to mix out as much but temps will be slightly cooler and heat index again peaks around 100 at worst. Thursday night into Friday morning, the major models depict a weak low partially or completely shearing off from the base of the trough near the Gulf Coast, and that will have the effect of stalling the front and perhaps reactivating it. Accordingly some PoP will linger in the Piedmont Thursday night after diurnal convection diminishes. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 305 AM Tue: Sfc high on the cool side of the front will migrate across the Northeast Friday into early Saturday. The influence of this high will keep temps relatively mild Friday but still actually a degree or two above normal. Low-level flow will turn easterly and then southeasterly; remnant of the front or weak low mentioned in the late short-term period should exit to the east as heights rise. The onshore flow will bring dewpoints a bit higher and suggests diurnal PoPs around climo, with some chances lingering overnight into early Saturday. This general evolution continues through Saturday, with temps and dewpoints ticking upward via airmass modification. PoPs also rise slightly. The real feature of interest for the period will be another trough passing the Midwest and carrying another front south and east. Global models/ensembles really agree fairly well on this occurrence, just varying in the timing thereof. The GFS is fastest, followed by the GDPS and then ECMWF, sometime between midday Sunday and late Monday morning. GFS is also the most bullish with precip coverage. Peak temperatures and PoPs are depicted Sunday, with slightly cooler and lower values Monday, but still above climo in both regards. Although dewpoint mixing will not be as effective within this pattern, a slight afternoon dip is likely. Values may edge above 100 each afternoon in the Piedmont, but Sunday would be the day of most concern with most areas outside the mountains rising to 100-104, with a few isolated spots perhaps exceeding 105. Any thunderstorms in the period, even near the fropa, likely will remain of the pulse or loosely clustered variety. PWAT values upwards of 150% of normal can be expected and a localized heavy rain threat is a reasonable bet, although dry soils may initially mitigate flood concerns. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... At KCLT and elsewhere: No good chance of flight restrictions across all TAF sites thru the period. The atmos will remain quite dry and only allow for Ci and some afternoon Cu today and Tue. A cold front will approach the wrn Carolinas late in the period, but any pre- frontal precip or lowering clouds will not affect KAVL or KHKY by 18z. Northeasterly to se/ly winds will remain light this evening with little to no gust potential, before going calm overnight. Winds pick up out of the southwest Wednesday ahead of the cold front and remain rather light, except for more moderate flow developing at KCLT by the late period. Outlook: A cold front will track over the terminals Wednesday night into Thursday before stalling south of the area on Friday, keeping SHRA/TSRA chances around the region. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...AR NEAR TERM...AR/SBK SHORT TERM...Wimberley LONG TERM...Wimberley AVIATION...SBK