Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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924 FXUS62 KGSP 040516 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 116 AM EDT Tue Jun 4 2024 .SYNOPSIS... Scattered afternoon showers and thunderstorms are expected again on Tuesday with temperatures warming back into the mid to upper 80s. Showers and thunderstorms will increase in coverage Wednesday into Thursday morning as a cold front crosses our area. Drier weather is expected to return by the end of the week and persist into the weekend, although a few isolated mountain showers will remain possible. && .NEAR TERM /THROUGH TODAY/... As of 113 AM Tuesday: Scattered showers and a few isolated lightning strikes continue to fester across the Upstate mainly along and north of I-85. This activity is expected to persist through much of the overnight within a moist environment. Patchy fog has also already developed across the mountains with widespread fog, some possibly dense, across the favorable valleys. The ongoing forecast captures this well and only a few minor adjustments were needed. Otherwise, a weak short wave ridge will progress steadily across the forecast area over the next 18-24 hours. Meanwhile, persistent SW low level flow is supporting quite moist conditions, with 12Z regional Raobs indicating precipitable water values at around the 75th percentile in terms of climatology. Strong insolation has resulted in moderate destabilization across the forecast area this afternoon, with sbCAPE of 1500-2000 J/kg analyzed across much of the CWA. Isolated convection is developing in the favored high terrain locations this afternoon, and coverage is expected to expand to at least widely scattered territory across the mtns, with more like isolated activity elsewhere, as the presence of the upper ridge should act to somewhat limit the overall coverage. Locally heavy rainfall will be the main threat, but mean cloud-bearing winds of around 15 kts should result in relatively progressive cell movement, keeping the excessive rainfall threat muted. Absence of robust instability will also limit the severe storm threat, but can`t rule out a stray pulse storm producing a microburst. While activity will diminish in coverage this evening, weak height falls and continued enhanced moisture is expected to result in some degree of coverage persisting across western areas into the overnight, with a continued threat of locally heavy rainfall. Min temps should be 2-4 degrees above climo. The upper ridge is forecast to have pushed east of the CWA by Tue afternoon, with the upper flow becoming increasingly cyclonic/open to passing vorticity lobes downstream of an upper low over the western Ohio Valley. If anything, moisture is forecast to increase further, while a consensus of guidance indicates another afternoon of moderate destabilization. These factors should support scattered to numerous coverage of diurnal convection...with PoPs ranging from 40-60% across much of the CWA. Although shear parameters will remain meager and cell movement rather progressive, the increase in "targets of opportunity" should yield an uptick in the threat for a couple of pulse severe storms and isolated excessive rainfall. Max temps will be a degree or two warmer than today. && .SHORT TERM /TONIGHT THROUGH THURSDAY/... As of 1245 PM Monday: The coverage of diurnally enhanced deep convection has the potential to remain numerous, especially acrs the mountains, into the evening hours on Tuesday, as synoptic scale forcing, in the form of subtle s/wv energy. lifts into the Tenn Valley. Regionally, the potential for strong tstms Tuesday night is mainly west of the mtns, within the zone of better flow and instability. The mean flow atop the cwfa through Wednesday is progged to be moderately fast with a subtle cyclonic curvature. Within a plume of developing instability and PWAT values nearing 2 inches, diurnally enhanced tstms should become widespread within this favorable pattern. Since there is the potential for storms to be blossoming and/or ongoing during the morning hours, it remains to be seen on just how unstable the atmosphere becomes. Select 12z short range model solutions depict moderate destabilization and given the progged shear, clusters of severe tstms are possible. A less than common June cool frontal passage is slated for Thursday. Sensible wx could wind up being limited to just morning showers along the front itself in the mountains, and then within the veered llvl flow and falling dwpts, deep convective redevelopment could hold off until the bndry translates to the coastal plain, we`ll see. Fcst sndgs continue to advertise developing deep mixing coincident and in the wake of the frontal passage, along with downslope warming. We will have to monitor for the possibility of max temps nearing 90 in parts of the piedmont. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 130 PM Monday: The SE CONUS is progged to be under the broad cyclonic flow within the southern periphery of closed upper low rotating toward the mid-atlantic at the start of the period. A dry continental airmass is progged to be in place, maintained by moderately deep mixing. Seasonably warm conditions are on tap for Friday, but accompanied by much lower than climo sfc dwpts. Closed upper low will wobble into the NE CONUS and eventually offshore over the weekend maintaining the seasonably warm and mostly dry conditions acrs the southern Appalachians within the NW and cyclonically curved flow limiting any daily small shower chances to just the nc mtns thanks to wrap around moisture or upslope. && .AVIATION /05Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: A busy TAF period is expected with restrictions expected at all terminals. Scattered showers and an isolated thunderstorm continue to fester early this morning with SHRA possible across the Upstate at KAND, KGMU and KGSP through the remainder of the overnight. Elsewhere, fog and low stratus has already developed at KAVL and will be possible at any given terminal through sunrise. Temporary visiblity and ceiling restrictions as low as LIFR will be possible. Fog will mix out after sunrise with any low stratus also scattering and lifting. VFR conditions will return area wide by mid morning, if not sooner. Thereafter, attention shifts to what is forecast to be a busy convective day with numerous afternoon showers and thunderstorms across the area. Temporary restrictions will once again be possible with any of this activity followed by another night of patchy fog and low stratus. Outlook: Coverage of diurnal convection is expected to increase Wednesday as a frontal boundary moves into the region. Morning low clouds and fog will also be possible Wednesday morning and Thursday mornings. Drier air will filter into the area Thursday afternoon and Friday morning, reducing chances for convection and restrictions, with relatively dry conditions continuing into the weekend. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...JDL/TW SHORT TERM...CSH LONG TERM...CSH/TW AVIATION...TW