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Area Forecast Discussion
617 FXUS62 KCHS 260005 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 805 PM EDT SAT JUN 25 2016 .SYNOPSIS... A cold front will shift slowly through the area tonight and Sunday before dissipating. Another front will impact the area beginning Tuesday, becoming nearly stationary into Wednesday then dissipating. Atlantic high pressure will rebuild Friday into the weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Main weather concern this evening will be the possibility of isolated severe thunderstorms as numerous mesoscale boundaries interact in an moderately unstable atmosphere with dry mid/upper levels which could lead to damaging winds. Otherwise, a weak cold front will advance slowly south through the area overnight while high pressure wedges inland across the Carolinas and into Georgia in its wake. A more stable air mass will gradually overspread the area from north to south, allowing convection to dwindle between sunset and midnight. Although the threat of severe weather will decline with sunset this evening, some showers and thunderstorms will be possible mainly near and south of the Savannah River and along the SC coast. Overnight low temps should cool into the low/mid 70s for most inland areas behind the front and some light fog will be possible. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... Sunday: A broad upper ridge will remain positioned over the central United States while surface high pressure sits off the New England coast. A diffuse frontal boundary will be pushing into the southern half of the area with slightly cooler and drier air moving in from the north. This will yield a high temperature map ranging from the lower 90s north to middle 90s south. The prevailing northeast flow will produce the best inland movement of the sea breeze across southeast GA. This is also where better low-level instability and boundary layer moisture will be present. We therefore show scattered showers and tstms, mainly in the afternoon, across far southern areas with lower coverage farther north. Severe potential appears nominal though an isolated severe storm is possible. Monday: Temperatures will rebound slightly as the in-situ front dissipates and Atlantic high pressure begins to rebuild. Dewpoints will likely mix out during the afternoon so only isolated convection is expected. Tuesday: Likely the most active day as the upper ridge flattens and a vort moves into the area during the day. A surface cold front is progged to move into the area from the west in the afternoon. Fairly deep westerly flow will precede the front so it may be dry for a portion of the day until the front draws closer. We therefore delayed the best pops until the afternoon. No convective indices are particularly impressive so the overall severe threat is low, but we could see some locally heavy rainfall. Highs will be in the low to mid 90s. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The long term forecast remains essentially unchanged and still revolves around the front that is expected to push into the area and become nearly stationary mid week. The front is then progged to remain in the vicinity of the forecast area through late in the week and will serve as a source of improved moisture and low level convergence to support increased coverage of showers and thunderstorms. For now, the forecast features mid to high range chance pops each day with lingering pops through the overnight. As the time draws closer and confidence grows in the placement of the lingering front, more detail can be put into the forecast for which periods are most likely to see the best rain chances. Highs will be around 90 each day with lows in the mid 70s. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... VCTS at KCHS around 00Z should end soon thereafter so we did not initialize with TS based on latest radar trends. Thunderstorms could impact KSAV through about 04Z but confidence too low to mention yet. Thunderstorms could produce strong winds and heavy rain. There is also a risk of mainly MVFR cigs and/or vsbys at both terms toward 12Z Sun as low- level moisture lingers behind a weak cold front, but again confidence too low to mention at this time. Extended Aviation Outlook: Low end chances for direct impacts from afternoon/evening thunderstorms on Sunday. Chances then will increase Tuesday through Thursday. && .MARINE... This Evening and Tonight: A cold front will slip into our South Carolina waters this evening, making it to Georgia waters late. Chances of showers and thunderstorms will be possible along/near the front, some possibly strong with damaging winds. High pressure will then wedge inland and push south/southeast in wake of the cold front. As a result, southerly flow at or below 10-15 kt should begin to back to the east/southeast late. Seas will range between 2-3 ft over most waters. Easterly winds Sunday will gradually shift to southeast on Monday, then south to southwest Tuesday and thereafter as Atlantic high pressure rebuilds. The strongest winds will be along the coast during the afternoon when a 10-15 kt sea breeze develops. && .CLIMATE... Charleston Airport tied the record high temperature of 99 degrees today set in 1977. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...RJB SHORT TERM...JRL LONG TERM...BSH AVIATION...DPB/RJB MARINE...DPB/JRL CLIMATE...