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Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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238 FXUS62 KCHS 011153 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 753 AM EDT Mon Jul 1 2024 .SYNOPSIS... A cold front will impact the area today into Tuesday before dissipating offshore. High pressure will return for the latter half of the week. && .NEAR TERM /THROUGH TONIGHT/... Today: Aloft, a large ridge will extend across the Central United States while a trough shifts off the Northeast and Mid-Atlantic coast by late morning. At the sfc, a cold front will be forced south across the local area as the mid-upper trough advances further offshore, encountering a very moist environment and spawning numerous to widespread showers/thunderstorms locally heading into peak diurnal heating hours. PWATs around 2.50 inches and slow storm motions along/ahead of the slow moving front could produce rounds of heavy rainfall this afternoon into early evening hours, particularly across coastal areas where moisture convergence and forcing are enhanced for a few to potentially several hours. Given a concern for prolonged rainfall in a favorably moist environment along with guidance (HREF in particular) trending slightly higher in regards to rainfall totals, a Flood Watch will remain in effect from noon to 9 PM for much of the area, with a focus for greatest concern being urban areas closer to the coast. Rainfall amounts of 2-4 inches should be common along with the potential for localized amounts up to 5-6 inches, especially near the coast. However, high rainfall rates will bring some concern for flooding across locations away from the coast as well, primarily along and east of the I-95 corridor. In fact, recent guidance continues to suggest the cold front to slowly push south across the local area this afternoon, then begin to stall across southern areas late. Should this occur, there will be an increasing concern for flooding across the Allendale County, SC to Tattnall County, GA stretch where roughly 2-4 inches of rainfall fell the previous evening/night. Should this scenario unfold, the Flood Watch could need to be extended across all counties. Outside of heavy rainfall, there remains a Marginal Risk for severe weather across the local area. Although widespread convection could limit the potential for stronger and/or severe thunderstorms today, there is a limited concern for stronger convection to occur across southern areas (southeast Georgia) later today where a longer duration of strong sfc heating takes place south of the arriving front and before anticipated showers/thunderstorms. DCAPE is not particularly impressive late day, but clusters of thunderstorms should eventually progress south and encounter an environment marked by SBCAPE around 2500 J/kg and weak 0-6 km bulk shear. In this area, a few thunderstorms could produce damaging wind gusts. The combination of high temps in the lower 90s and sfc dewpts in the mid-upper 70s will also lead to heat indices approaching 103-107 this afternoon, but given the likelihood of widespread showers and thunderstorms, conditions should remain shy of Heat Advisory criteria. Tonight: By mid evening, convection will trend weaker and wane overnight, although some showers and thunderstorms could persist across far southern areas should the front stall and/or linger nearby prior to daybreak. A northeast wind post fropa and previous shower/thunderstorm activity will lead to noticeably cooler low temps. In general, lows will range in the upper 60s/lower 70s well inland to mid-upper 70s near the beaches. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... A stalled front will linger just off the coast and to the south near the Altamaha on Tuesday. The front is expected to become more diffuse through the day on Wednesday. Aloft, a mid level ridge centered over the Gulf coast states will expand over the local area with time as troughing offshore shifts further away. Scattered to numerous showers and thunderstorms will be possible each day, with highest coverage over southeast Georgia where deeper moisture of PWats >2 inches is expected to still reside. Locally heavy rainfall is possible. Areas further inland and to the north should not see as much activity. There will be notable relief from the heat, especially on Tuesday when highs only peak in the mid 80s. Lows both nights will mainly be in the low to mid 70s. Atlantic high pressure will prevail on Thursday, while a trough of low pressure develops inland. Upper ridge settling overhead will help limit convection with just isolated to scattered showers and thunderstorms possible with the sea breeze. Temperatures will rise back up to the low to mid 90s, but heat indices should remain in check below headline criteria (peaking 100-105F). && .LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... Strong upper level ridge initially overhead will transition offshore through the weekend. The surface will feature troughing inland and high pressure offshore. Main concern this period will be the heat. The pattern will favor increasing temperatures and humidity. Some interior locations could even see max temperatures hit triple digits. Excessive heat headlines are certainly possible. Otherwise, isolated to scattered diurnally-driven showers and thunderstorms are expected. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... KCHS/KJZI/KSAV: Lingering low clouds have resulted in the need for TEMPO MVFR cigs to be included at JZI/SAV between 12-14Z. VFR conditions should then prevail at all terminals into late morning hours. However, the next chance for convection and prolonged flight restrictions will occur Monday afternoon as a cold front slowly moves over and/or stalls across the area. Showers and thunderstorms, some possibly moderate to heavy rain producers, are expected to impact all terminals by 19Z Monday, then persist for at least a few hours into early evening. TSRA remains at all terminals during this time frame, followed by SHRA Monday evening. Tempo IFR cigs/vsbys are possible during thunderstorms and will likely be added in future TAF amendments as timing of direct impacts becomes more clear. Precip should come to an end by 03-04Z Tuesday, but flight restrictions will remain at all terminals with at least MVFR cigs through 12Z Tuesday. It`s possible some IFR cigs could occur at any terminal for a few hours prior to 12Z Tuesday. Extended Aviation Outlook: Flight restrictions in low clouds could linger into Tuesday. Otherwise, brief flight restrictions are possible in showers and thunderstorms, mainly in the afternoon and evenings through the period. && .MARINE... Today and Tonight: A cold front will shift south across the area this afternoon, turning south/southwest winds to east-northeast in its wake by tonight. Widespread showers and thunderstorms could also reduce vsbys across local waters to 1 NM of less at times and produce gusty winds, some of which could necessitate Special Marine Warnings. There will be a bit of a post-frontal surge tonight with speeds increasing to 15-20 kt over the South Santee to Edisto Beach nearshore leg and 10-15 kt elsewhere. Seas should also build upwards to 3-5 ft tonight (highest across Charleston County waters late). Tuesday through Saturday: Gusty northeast winds are expected on Tuesday in between high pressure inland and a stalled front offshore, especially across the Charleston county waters. Conditions look to hold below small craft advisory criteria. Gradient weakens for mid to late week with winds 15 knots or less and seas averaging 2-3 ft. && .CLIMATE... Daily Rainfall Records for July 1: KCHS: 2.66 set in 1948 KCXM: 1.64 set in 1966 KSAV: 2.76 set in 1871 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Flood Watch from noon EDT today through this evening for GAZ101-116>119-137>141. SC...Flood Watch from noon EDT today through this evening for SCZ042>045-047>052. MARINE...None. && $$ NEAR TERM...DPB SHORT TERM...ETM LONG TERM...ETM AVIATION...DPB/ETM MARINE...DPB/ETM