Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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004 FXUS62 KCHS 050826 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 426 AM EDT Fri Jul 5 2024 .SYNOPSIS... High pressure will persist through Friday, then a weak cold front will stall over the area this weekend and linger through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, subtle h5 vort energy will exit offshore and to the south along the eastern edge of a ridge while an upper low remains well offshore across the western Atlantic. At the sfc, high pressure across the western Atlantic will extend across the Southeast United States for much of the day, but should gradually nudge east while some lee troughing takes place inland. Despite large-scale subsidence associated with a the mid-upper lvl ridge and light west/southwest winds aloft in place, strong sfc heating co-located with PWATs around 2.0 inches and SBCAPE between 1500-2000 J/kg along with lee troughing, should be sufficient to initiate convection just inland to the local area, and eventually result in isolated to scattered showers/thunderstorms drifting east across far inland zones locally by mid-late afternoon. Shear remains weak throughout this time frame, so activity will be driven by daylight heating and be primarily pulse type in nature, but clustering of thunderstorms and/or outflow boundary interactions could allow convection to persist shortly after sunset. A stronger thunderstorm can not be ruled out given strong sfc heating. Showers and thunderstorms far inland could very well provide some relief to the heat mid-late afternoon for what appears to be the warmest area of the day based on 1000-850 mb thicknesses and ample sfc heating before convection occurs. However, sfc temps are still expected to approach the mid-upper 90s away from coastal areas today, and could even touch 100 degrees briefly across far interior locations along a stretch from Allendale County to Jenkins County. Low-lvl dry air depicted on soundings along with large-scale subsidence aloft suggests that some mixing out of sfc dewpts takes place heading into peak heating hours, and sufficiently so for heat indices to remain just below Heat Advisory criteria, generally in the 104-107 degree range. The exception could be well inland where warmest temps are expected this afternoon before the arrival of clouds/precip and/or along an inland advancing seabreeze, where moisture pools temporarily and sfc dewpts remain in the mid 70s during peak heating. However, the duration and coverage of these events appears too short to justify a Heat Advisory locally at this time. Tonight: Any convection that has developed and/or drifted across far inland zones should struggle to persist given a loss of diurnal heating and weak shear in place. Those that do persist, could last an hour or two post sunset, mainly due to outflow boundary interactions. The rest of the night will remain rather quiet, but mild ahead of a front approaching from the northwest this weekend. In general, lows should range in the mid-upper 70s inland to lower 80s at the beaches. && .SHORT TERM /SATURDAY THROUGH MONDAY/... The upper ridge will be centered over northern Florida on Saturday while a weak shortwave rotates around the northern periphery during the afternoon. A weak cold front is forecast to drop southeast into the area during the day, then stall nearby through early next week. The greatest moisture and instability will be across inland areas on Saturday which is where we show the greatest coverage of showers and thunderstorms. High temps in the mid 90s with mid/upper 70s dewpoints will produce heat indices 105-110F for several hours during the afternoon in most locations. Dewpoints could mix out just enough far inland to keep heat indices below 105 in those areas. A Heat Advisory will likely be needed for much of the area. Additional shortwaves moving in from the west Sunday and Monday will break down the upper ridge, reducing high temps by a couple degrees. The deep moisture is expected to expand eastward, with the entire area under at least 2.1" PWATs. Considerable coverage of showers/tstms expected both days. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... A fairly wet pattern likely to persist for much of next week due to deep tropical moisture in place, continual shortwaves, and a weak convergence axis along the decaying cold front. The greatest coverage should be during the afternoon and evening hours. Wednesday looks like the hottest day during this period, with the potential for Heat Advisories. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... VFR conditions are expected to prevail at CHS/JZI/SAV terminals through 06Z Saturday. Extended Aviation Outlook: Brief flight restrictions are possible in showers and thunderstorms, mainly in the afternoon and evenings, this weekend through the middle of next week. && .MARINE... Today and Tonight: After some nocturnal surging weakens early this morning, high pressure extending across local waters from the northeast along with lee troughing taking place well inland should favor a modest pressure gradient across local waters. In general, southwest winds will turn more south-southeast this afternoon, peaking around 15 kt, highest near the coast where a seabreeze develops and shifts inland. Overnight, a slightly weaker southerly wind takes place (10-15 kt) with high pressure continuing across local waters well in advance of the approaching front this weekend. Seas will range between 2-3 ft through tonight. Saturday through Wednesday, a typical summertime pattern will persist, with prevailing southerly flow and winds/seas well below advisory thresholds. Rip Currents: A swell of 2 feet every 10 seconds and proximity to the new moon will maintain a Moderate Risk for rip currents for all beaches today, and likely through Saturday due to lingering 2-3 feet swell every 9 seconds and onshore winds. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...JRL LONG TERM...JRL AVIATION...DPB/JRL MARINE...DPB/JRL