FXUS62 KCHS 270557 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 157 AM EDT Sat Jul 27 2024 .SYNOPSIS... A cold front will drop south across the area Saturday, followed by the return of broad high pressure for much of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As 155 AM, satellite nighttime microphysics RGB and ground based observations indicated an expanding area of stratus over portions of the CHS Tri-county. It is possible that some patchy fog may develop with stratus build down later tonight. At the time, the forecast update will feature adjustments to hourly sky. Otherwise, convection should remain over the adjacent Atlantic waters, with dry conditions over land. Lows are forecast to reach the low 70s inland, ranging to the mid to upper 70s along the coast. && .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/... Saturday: The region will be positioned under the broad cyclonic flow aloft between upper ridging centered over the Florida Panhandle and the sharpening trough propagating off the U.S. East Coast. A weak cold front will continue to slide south into Southeast Georgia during the morning hours, becoming situated south of the Altamaha River by late afternoon-early evening. Drier air characterized by lower 850 theta-e values will attempt to advect south during the afternoon hours, but surface dewpoints looks to remain elevated (70s) with PWATs holding around 2 inches. The deepest moisture, low- level convergence and better instability look to occur over Southeast Georgia, closer the front itself. CAMs have trended slightly drier over the past 24-hours and the forecast will feature lower pops again this cycle given this trend. Pops will range from 20% well inland to 30% over south coastal South Carolina with 30-50% over Southeast Georgia, highest across the middle/lower Georgia coastal counties. Further downward adjustments may be needed. A risk for locally heavy rain will exist, but storms look to remain progressive enough to limit any flooding to low- lying and poor drainage areas. Convection will quickly wane by early evening with dry conditions expected overnight. Highs will peak upper 80s/lower 90s away from the beaches with overnight lows ranging from the upper 60s/lower 70s well inland to the upper 70s/near 80 at the beaches. Sunday: Drier air from the north will further infiltrate the area with the front displaced well to the south and the upper ridge aloft builds. Dewpoints are expected to mix out into the mid-upper 60s as high pressure noses in from the northeast with a few lower 70s noted along the Altamaha River. This coupled with considerably lower mean moisture values and lower 850 hPa theta-e should support a considerably lower risk for showers/tstms--the lowest in some time. Pops will range from 10% across most of Southeast South Carolina with 20-40% over Southeast Georgia, highest near the Altamaha River. These too many prove too high if trends continue. Highs will warm into the lower 90s away from the beaches with overnight lows ranging from the upper 60s/near 70 well inland to the upper 70s/near 80 at the beaches. Monday: Moisture values will begin to creep up as high pressure slides farther offshore and the low-level flow becomes more onshore with time. The best chance for afternoon/evening showers/tstms will be confined across the interior given the sea breeze should be fairly progressive during the afternoon hours. Pops were limited to 20-40% away from the immediate coast with the highest pops clustered over far interior Southeast Georgia where net instability and low- level moisture will be the greatest. Highs will warm into the upper 80s/lower 90s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... The pattern will trend into a more typical diurnally driven convective pattern for much of next week. Models show a broad mid-level weakness developing by mid-week which could help enhance convection a bit with convection concentrating inland each afternoon/evening ahead of the sea breeze. Chance pops look reasonable through period, close to climatological normals for deep summer. Temperatures will generally run near seasonable normals, but there are signals the heat and humidity will begin to build Thursday into Friday. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... Prior to the 6Z TAFs, satellite nighttime microphysics RGB and ground based observations indicated an expanding area of stratus over or approaching the KCHS and KJZI terminals. Both TAFs will feature restrictive ceilings, as low as LIFR through the rest of tonight. KSAV is expected to see a period of IFR ceilings around dawn, highlighted with a TEMPO from 9-13Z. MVFR ceilings may linger until late this morning. A backdoor cold front is timed to pass over the terminals during the mid- day, followed with wind veering from the NE. Isolated to scattered showers, possibly a thunderstorm, may develop near the cold front. Each TAF will feature a mention of VCSH during the late afternoon into this evening. Extended Aviation Outlook: A typical late summer shower/tstm regime will dominate for much of the period with afternoon/evening showers/tstms potentially posing a risk to KCHS, KJZI and KSAV. && .MARINE... The surface pattern should support southwest winds between 10 to 15 kts across the marine zone this afternoon. Seas are forecast to range between 2-3 ft. A weak cold front is forecast to push over the coast waters before dawn Saturday. Ahead of the cold front, winds will remain from the southwest between 5 to 10 kts. In the wake of the front, winds will turn from the west around 10 kts. Seas should remain between 2 to 3 ft. Saturday: A cold front will slip south through the waters Saturday resulting in winds turning north to northeast during the day. Speeds in the South Santee-Edisto Beach nearshore leg could see speeds as high as 15 kt with gusts to 20 kt by Saturday night. Otherwise, speeds will hold less than 15 kt across all remaining waters. Sunday through Wednesday: Winds will turn easterly for Sunday as high pressure to the north slides offshore. More southerly winds return by mid-week as the waters become situated along the western flanks of Atlantic high pressure. Speeds look to remain less than 15 kt through the period with seas less than 4 ft, although a few 5 footer could brush the Georgia offshore waters near 60 NM at times Sunday into Sunday night. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM... LONG TERM... AVIATION...NED MARINE...