Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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384 FXUS62 KCHS 051459 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1059 AM EDT Wed Jun 5 2024 .SYNOPSIS... High pressure will extend across the area through today. A cold front will approach from the northwest on Thursday, then slowly move through on Friday. High pressure returns for the weekend, then another cold front will move through Monday. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, the axis of a ridge will remain placed offshore across the western Atlantic in advance of h5 shortwave energy nudging into the local area this afternoon. At the sfc, high pressure extending across the area from the western Atlantic will remain the primary feature throughout the day, limiting forcing mechanisms to trigger convective development late morning and perhaps into early afternoon. Latest hi-res models continue to indicate showers and thunderstorms developing across far interior GA zones and upstream of the local area early afternoon as h5 shortwave energy encounters deepening moisture (PWATS around 1.75 inches) and an axis of SBCAPE around 2500 J/kg during peak diurnal heating hours. Bulk shear remains rather weak as this occurs, but a few loosely organized thunderstorms could become strong and/or perhaps marginally severe mid-late afternoon across inland Georgia/South Carolina, with damaging wind gusts being the primary concern given low-lvl lapse rates near 8-8.5 C/km and DCAPE around 800 J/kg in the vicinity of convective development and expected tracking/motion. Outflow from this activity combined with a late day seabreeze circulation could drive some convection east-northeast across southeast South Carolina late day, but the general consensus is that activity will likely weaken/wane heading by early evening hours with the loss of stronger diurnal heating. High temps should range in the upper 80s to lower 90s today, warmest away from the immediate coast. Tonight: As the early evening begins, there will likely be ongoing thunderstorms that extend southward from between Allendale and Walterboro to the entire southeast Georgia coast. This activity could continue to spread eastward through the evening, especially if outflow boundaries can track into untapped area of southeast South Carolina. We will have to wait and see how thunderstorms evolve through the afternoon, but it is possible there could be more coverage through the evening into southeast South Carolina than currently depicted in the forecast. Any severe threat should steadily diminish with the loss of heating. The focus for showers and thunderstorms should then shift offshore for the latter part of the overnight. Look for mild temperatures, with lows likely not falling below 70 in most areas. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... A weak shortwave will move through Thursday afternoon and evening, then a cold front will cross the area Friday morning. Deep moisture will exist over the area Thursday with PWATs around 1.75". Decent instability will develop in the afternoon given high temps in the low to mid 90s, though some mixing out of dewpoints inland will somewhat reduce total buoyancy. Low- level flow out of the WSW will keep the sea breeze pinned near the coast for much of the day, then it may move slightly inland late in the afternoon. Weak mid-level subsidence may develop during the afternoon as the shortwave trough axis shifts to the coast. This may be why much of the guidance only shows scattered convection on Thursday. We bumped PoPs down a tad, though still anticipate at least 40-50% coverage at some point on Thursday. Considerably drier air will move in on Friday. Downslope flow will push highs into the low to mid 90s, but surface dewpoints dropping into the upper 50s inland to lower 60s coastal will make for a noticeable change in airmass. Another weak shortwave will drop through the area Friday afternoon. Although subsidence and drier air should severely limit the convective potential, we could have just enough moisture across the southern half of the area to support an isolated shower or tstm. Saturday looks dry. Downslope flow will again push highs into the lower 90s, though the air will feel relatively dry given surface dewpoints mixing down into the 50s during the day. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... Another cold front will approach on Sunday, then stall near the area Monday before eventually dissipating. Moisture will be on the increase late weekend into early next week. This, along with some shortwaves and decent sea breezes each afternoon, should support scattered convection. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... VFR conditions are expected to prevail at KCHS, KJZI, and KSAV through 12z Thursday. The main forecast challenge will be afternoon and evening shower and thunderstorm activity and if it can impact any of the terminals. KSAV seems to be the primary candidate and we have introduced VCTS with a TEMPO for TSRA in the 21-00z time period. For now we have kept the TEMPO MVFR, but it is likely that if a storm directly impacts the terminal the visibility will at least briefly drop to IFR. Gusty winds are also a concern. This thunderstorm activity could shift eastward into the vicinity of KCHS and KJZI later in the evening, but confidence is too low to add anything into the TAF`s at this time. Extended Aviation Outlook: Aside from brief flight restrictions in showers/tstms Thursday afternoon, VFR conditions expected. && .MARINE... Today and tonight: Southerly flow will prevail across the local waters through the period with speeds mostly in the 10-15 knot range. Gusts up to around 20 knots are expected along the land/sea interface with the afternoon sea breeze. Overnight, winds will pick up a bit thanks to modest nocturnal surging, with speeds around a solid 15 knots or even 15-20 knots at times. Seas are expected to average 2-3 feet. SW winds Thursday and Thursday night will transition to W on Friday, then a brief period of northerly flow expected Friday night and Saturday behind a cold front. Winds return to southerly by late weekend as Atlantic high pressure rebuilds. No headlines anticipated. && .TIDES/COASTAL FLOODING... Astronomical tides will remain elevated today and again on Thursday. Although the wind direction along the coast isn`t ideal for driving large positive tidal departures, conditions should still be sufficient to produce departures in the 0.4 to 0.6 ft. Therefore, the upcoming evening high tide and again Thursday evening could peak right around 7.0 ft MLLW in Charleston. Coastal Flood Advisories could be needed for Charleston and coastal Colleton counties. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...JRL LONG TERM...JRL AVIATION...BSH/JRL MARINE...DPB/JRL