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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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752 FXUS62 KGSP 161016 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 616 AM EDT Tue Jul 16 2024 .SYNOPSIS... Hot high pressure lingers above the region through Wednesday. A pattern change begins to evolve later Wednesday, as a cold front will approach from the northwest then become stationary across our region for several days. This will keep shower and thunderstorms chances elevated through at least the end of the week. && .NEAR TERM /THROUGH TONIGHT/... As of 545 AM Tuesday: Not much change for the morning update as the CWA is clear of any showers and temperatures remain on track as forecasted. Satellite shows a swath of stratus forming across the Upstate and into the NC Piedmont. Current sky trends should dissipate after sunrise. Otherwise, hot temperatures and high pressure continues in the near term. Flow aloft remains weak Tuesday with a continuation of moisture advection from the SW sfc winds. Not expecting too many clouds overnight, outside of some low-level stratus over areas that received rainfall yesterday. Instability increases throughout the day with ample heating at the surface. Guidance from modeled soundings show a more modest inverted-V in the BL and around 1000- 2000 J/kg of sbCAPE. CAMs once again are having trouble depicting afternoon convection, but scattered showers and thunderstorms are possible, with the highest chances over the mountains (60%-74%). Though the risk for severe weather is low, cannot rule an isolated severe storm or two. Aside from storm chances, heat is the bigger story for Tuesday. There is less dry air aloft to mix down during the daytime, which suggests hot temps and hotter heat index values likely. There is a catch though. if showers can get going, this could reduce heat index values in a few of the areas and provide some relief. But, considering the impacts, a Heat Advisory will be in effect from noon through 8 PM for Cabarrus, Mecklenburg, and Union (NC) counties. By Tuesday night, PoPs ramp down quickly and humidity remains high, keeping overnight temps in the mid 70s. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 245 am Tuesday: Heights will steadily fall across the eastern half of the country during the short term, with a long wave trough expected to be centered from the western Gulf of Mexico through the northeast Conus by the end of the period. The leading edge of an associated baroclinic zone is expected to sag across the TN Valley during the day Wednesday. Hot and muggy conditions are again expected across our area in advance of this front...although heating and instability may be somewhat tempered by increasing clouds. This makes one more day of Heat Advisory conditions possible...but hardly a slam dunk in the Charlotte metro area. Moderate instability and continued elevated precipitable water values of around 2" should allow for good coverage of diurnal convection...while widespread, pre-frontal convection may roll into western areas by the end of the day. Likely PoPs are therefore advertised across the Piedmont/ foothills, with around 80% chances expected across the mountains. Instability should be sufficient to support a handful of pulse severe storms, while the primary threat may prove to be locally excessive rainfall in light of the high moisture content. With the front likely making a push into the CWA overnight Wed/early Thu, Wed night should remain convectively active to some extent, with continued potential for locally excessive rainfall. The frontal zone is expected to sag southeast across the CWA on Thursday, although how fast this occurs is the subject of some controversy...making for a somewhat problematic convective forecast, as some short term guidance sources indicate sufficiently low theta-E air will advect into the mountains/perhaps the northern zones to preclude much in the way of a threat. There`s a good enough signal to advertise a 70 PoP across much of the area, but this will likely need some refinement in the near future. The expectation of more extensive cloud cover Thu may further constrain the severe storm potential. However, virtually boundary-parallel storm motions/ increased potential for cell training, and continued very high moisture content may increase the excessive rainfall threat. The consensus in guidance is strong enough to anticipate the front sagging south of the area Thu night...resulting in diminishing chances for convection. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 310 am Tuesday: A portion of the upper trough (mentioned above) is expected to separate from the main branch of the subtropical jet...possibly evolving into a closed low over the lower Miss Valley and vicinity early in the period. This will allow the old frontal boundary to persist in or near our CWA through much of the period, while deep SW flow will support continued high precipitable water values. The upshot for our forecast area will be cooler (near-to-a-little below normal temperatures) and convectively quite active weather, with at least likely PoPs in the forecast each day. While there will certainly be a diurnal trend to convective activity, the pattern will be such that the overnight/early morning hours could remain at least somewhat active. The main hazard concern will be locally excessive rainfall, especially as hydrologic conditions steadily deteriorate...at least on a localized basis. && .AVIATION /10Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: VFR conditions prevail for most sites through the end of the TAF period. A swath of mid level stratus should dissipate after sunrise and lead to SCT or even SKC. Another afternoon chance for showers and TSRA at all terminals, therefore a PROB30 during the afternoon and into early evening hours. Moderate confidence for the KAVL site so went ahead and gave a TEMPO for TSRA from 17z-21z. As for winds, speeds should remain relatively light and prevail SW. During the afternoon, winds could become VRB should any TSRA develop with a brief period of gusty winds near these storms. Any showers or TSRA looks to be out of the area after 00z with sites continuing VFR conditions. There is a possibility for vsby restrictions for BR at mountain sites, but confidence is low at this time. Outlook: An uptick in showers and thunderstorms Wednesday onward as a cold front approaches and stalls near the region. Morning fog/low stratus possible each morning, especially across the mountain valleys and for areas that received heavy rainfall the day prior. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...Heat Advisory from noon today to 8 PM EDT this evening for NCZ071-072-082. SC...None. && $$ SYNOPSIS...JDL NEAR TERM...CP SHORT TERM...JDL LONG TERM...JDL AVIATION...CP