Area Forecast Discussion
Issued by NWS Charleston, SC

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000 FXUS62 KCHS 081925 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 325 PM EDT Sat Aug 8 2020 .SYNOPSIS... A stationary front will linger to the west through the weekend before dissipating. The region will then be positioned between Atlantic high pressure centered offshore and an inland area of broad low pressure. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Through Sunset: Afternoon temperatures in the 90s are combining with plenty of moisture (PWATs ~2") to fire off convection. CAMs seem to focus it in two different areas. One area is along the sea breeze as it moves inland. The other area is over central GA, with the convection shifting towards our GA counties and coast during the evening. We have this all accounted for in the POP grids, but should note that some of the models have trended a bit drier. Though, we kept the POPs in the chance category. SPC Mesoscale Analysis shows MLCAPEs peaking in the 2,500-3,000 J/kg range in the next few hours. Additionally, DCAPEs will be 1,000-1,200 J/kg. Marginally severe pulse thunderstorms with damaging winds gusts remain a concern into the evening. Additionally, weak steering flow aloft will equate to very little storm movement, so locally heavy rainfall is expected. Outflow boundaries and the sea breeze will drive the convection into this evening. Tonight: Very little change is anticipated in the mid-level pattern. Meanwhile, a stationary front will linger to the west of our area. Any remnant convection over land during the evening hours should dissipate. The focus for convection then shifts over the coastal waters. Though, the models differ on the coverage. We leaned more towards the CAMs, which show minimal coverage. This equates to slight chance POPs. Low temperatures should range from the low to mid 70s inland and the upper 70s at the immediate coast. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... Sunday: Short term guidance indicates that the axis of a H5 trough will ripple over the forecast area during the afternoon and evening. At the sfc, the CWA will remain between high pressure centered over the western Atlantic and a trough just east of the Fall Line. A sea breeze should develop during the late morning, sliding inland during the afternoon and evening hours. HREF indicates that showers and thunderstorms will develop along and west of the sea breeze and ahead of the H5 trough. Thunderstorms coverage appears the greatest during the late afternoon into the early evening, PoPs generally ranging between 50-70 percent. Given the broad area of llvl convergence and PW around 2 inches, high resolution guidance indicates that some areas could see rainfall amounts exceed 2 inches. High temperatures are forecast to range from around 90 along the coast to the mid 90s across inland GA. Peak Heat index may favor values around 105 degrees over the coastal counties. Convection should generally dissipate during the late evening hours. Low temperatures are forecast to range from the upper 70s along the coast to the mid 70s inland. Monday and Tuesday: The mid level trough will remain over the region and ridging builds to the west. The sfc pattern should support the formation of a sea breeze both days. Given a broad field of instability and deep moisture, the environment should yield scattered to numerous thunderstorms each afternoon. High temperatures are forecast to range from 90 near the coast to mid 90s inland. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Little change in the large scale pattern, with a deep layer Atlantic ridge situated to the east and deep layer trough of low pressure well to the west. Global models show that an upper trough may try to sharpen well to the west during this period, as well as an increase in deep layer moisture. With this combination, guidance continues to show likely afternoon/early evening PoPs each day. A little uncomfortable going with such high PoPs this far out, but blended PoPs have been consistently high, and those PoPs collaborate well with surrounding offices. Highs will continue near normal, around 90 to the lower 90s. Lows in the lower to mid 70s. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... 18Z TAFs: Both TAF sites start out with VFR. Hi-res models indicate thunderstorms could bring brief flight restrictions to either TAF site later this afternoon into this evening, possibly as late as 01-02Z. Given this large time window, we opted to maintain the VCTS until then. If radar trends indicate a direct impact, then an amendment will be made to add a TEMPO group. Otherwise, the thunderstorms are forecasted to dissipate this evening, followed by a dry night. Another round of convection is possible Sunday afternoon. Extended Aviation Outlook: Scattered to numerous thunderstorms will develop over the Coastal Plain each afternoon and evening. It is possible that brief flight restrictions could occur with the passage of any thunderstorm. Areas of heavy rain could see fog or stratus develop during the pre-dawn hours. && .MARINE... Tonight: S winds 10-15 kt in the evening will veer to the SW and ease to around 10 kt after midnight. Seas will be around 2 ft. Sunday through Wednesday: The sfc pattern will feature high pressure centered over the western Atlantic and broad low pressure inland. This pattern should generally support south winds between 10 to 15 kt and seas between 1-2 ft. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...NED LONG TERM...RFM AVIATION...NED MARINE...NED is the U.S. government's official web portal to all federal, state and local government web resources and services.