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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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548 FXUS62 KGSP 072335 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 735 PM EDT Sun Jul 7 2024 .SYNOPSIS... A weak surface front will increase the chance for thunderstorm activity across the area this afternoon and evening. An active pattern of afternoon and evening showers and storms is expected to continue for the first half of this week. More typical mid-July weather is expected toward the end of the week. && .NEAR TERM /THROUGH MONDAY/... As of 530 PM Sunday: For the evening update, widespread showers and thunderstorms are currently moving off the mountains toward the SE. Increased PoPs (50%-70%) through the NC Piedmont, off the foothills as ongoing convection is continuing to develop. A few severe thunderstorm warnings were issued for Greenville, Spartanburg, and Polk Counties and quite a number of SPS`s. Conditions remain favorable for the next few hours to support heavy rainfall and strong gusty winds where these storms develop. Otherwise, the synoptic pattern remains relatively unchanged with broad longwave troughing draped across much of the country from the Northern Rockies to the Ohio Valley. Stout upper ridging remains centered over California along with another upper ridge over the Atlantic, the western flank of which nudges into the southeast states. An upper low associated with a tropical upper tropospheric trough also continues to spin off the Carolina coast, but will be of no impact through the near term period. At the surface, very moist southerly onshore flow continues with a previously stalled frontal boundary having lifted back north into the foothills north of the I- 40 corridor. The boundary is rather diffuse, however, and nebulous in surface observations with location being determined by a subtle moisture gradient and weak low-level surface convergence. Ample moisture and warming into the upper 80s to low 90s has resulted in moderate instability this afternoon with convection blossoming across the mountains and along the boundary across the I- 40 corridor. With time, convection over the mountains is expected to become loosely organized along composite cold pools with several linear structures moving out of the mountains and into the Upstate and foothills and eventually portions of the Piedmont. 2500-3000 J/kg of surface-based CAPE has been realized on area ACARS soundings, which will be sufficient for several stronger updrafts and the development of a mature cold pool. Instability profiles are very tall and skinny, however, with poor lapse rates and limited DCAPE. A modified 12z Peachtree City, GA sounding supported a microburst composite value of 3, which combined with aforementioned parameter space would be supportive of a few isolated severe thunderstorms with locally damaging winds. The main threat will be across the southern mountains, northeast Georgia and the Upstate with this area being placed in a marginal risk for severe storms from the Storm Prediction Center. Convection will push out of the area this evening with at least a few isolated to scattered showers lingering into the late evening hours. Thereafter, a widespread deck of low stratus clouds is expected to build in given a rather moist boundary layer with areas of fog also possible. Heading into tomorrow, extensive morning clouds will likely delay daytime heating and the atmosphere will also remain worked over from today`s storms. Thus, the CAMs are not overly enthused with the coverage of storms, especially outside of the mountains. Several storms appear likely over the southern mountains/escarpment with only isolated to scattered showers and storms elsewhere. Temperatures will be in the upper 80s to low 90s tomorrow, but could end up a degree or so cooler if morning clouds take longer to lift and scatter. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... As of 155 pm Sunday: A deep/weak SW flow will remain over the southern Appalachians and vicinity through the short term...between an anomalous trough across the central Conus...and a subtropical ridge nosing into the Southeast from the western Atlantic. Resultant quiescent, but very moist atmosphere will continue to support higher-than-normal coverage of diurnal convection...PoPs mainly 60-70% across the mtns and 50-60% across the Piedmont...through the period. Diurnal instability is forecast to be adequate for isolated pulse severe storms...perhaps more than adequate on Wed, when a consensus of short term guidance indicates sbCAPE will peak at around 3000 J/kg. One change that is expected is that storm motions should become a bit swifter, especially on Wed afternoon. This will be a consequence of the acceleration of the mid-level flow as the upper trough draws a bit closer...as the circulation associated with the remnants of T.C. Beryl is expected to become absorbed into the westerlies...and progresses the central Conus trough to the east. Nevertheless, the very moist conditions, locally poor antecedent conditions, and the potential for SW=>NE training cells will result in a continued low-end threat for excessive rainfall. Temps are forecast to be a couple of degrees above normal through the period. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 210 pm Sunday: The global models continue to trend (unfortunately) toward a drier extended period, as upper trough is expected to progress into the eastern states...albeit weakening and lifting north of our area over the subtropical ridge. It`s looking increasingly likely that the proximity of the trough will allow the deeper/subtropical moisture to shunt east of the CWA during the latter half of this week, resulting in dwindling chances for convection. Daily instability and moisture should still be adequate for diurnal showers and storms, but with coverage more typical for the time of year. Daily PoPs therefore trend closer to climatology for much of the period, with standard mid-July threats of a pulse severe storm or three and locally excessive rainfall. Temps are forecast at near-to-slightly-above normal through much of the period. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... At KCLT and elsewhere: Ongoing TSRA will start to taper off are all terminals through midnight, with lingering VCSH afterwards. All terminals had rain this evening and this will pose a higher confidence in VSBY/CIG restrictions during the overnight hours. Patchy BR is expected at all sites east of the mountains with FG possible at KAVL, with a TEMPO for 1sm VSBY from 09z-13z. Most other sites also have a TEMPO for a VSBY of 4sm and IFR CIGS during this time. Conditions should improve after daybreak, but will be slow given the deep amount of moisture in the area. Once VCSH/TSRA taper off, winds will become VRB or calm through the overnight hours, enhancing FG/BR potential. Winds should prevail more southerly once speeds start to pick up outside the mountain zones. There is a chance for another round of convection Monday evening, but coverage is not expected to be as widespread. PROB30 for this at all sites except KHKY, where confidence is the lowest. Outlook: An active summertime pattern continues for most of the upcoming week, leading to showers/thunderstorms and possible restrictions each afternoon/evening. Fog or low stratus may develop each morning, especially over areas that received rain the previous day. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JDL NEAR TERM...CP/TW SHORT TERM...JDL LONG TERM...JDL AVIATION...CP