Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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238 FXUS62 KCHS 011043 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 643 AM EDT Wed May 1 2024 .SYNOPSIS... A weak disturbance will move off the coast this morning. High pressure will then prevail through Friday. A series of disturbances will move through Saturday through Monday, then high pressure will rebuild. && .NEAR TERM /THROUGH TONIGHT/... Today: A well defined short wave that is easily observed on water vapor imagery will pull off the South Carolina coast early this morning. This is replaced by ridging that approaches from the west. The surface pattern is rather nebulous, with the western edges of the Atlantic high staying over the ocean, and a subtle surface trough nearby. Patchy dense fog will be around early this morning due to calm winds and plenty of low level moisture. This is generally far inland, and will mix out by 9 am. With the passage of the short wave, showers during the early morning across the Charleston quad-county district will come to an end. NVA in wake of that feature, subtle height rises, and a weak cap will keep things rainfree into early afternoon. However, once we reach our convective temperature in the lower 80s, which will be reached around 1-2 pm, convection will start initiating along almost pure sea breeze. While there is good low level lapse rates, the mid level lapse rates are only so-so, and CAPE and shear is on the weaker side. These conditions along with limited buoyancy will only be able to produce isolated to scattered showers and a few t-storms. This is mainly over the eastern half of the forecast counties, tied to the sea breeze inland motion. It`ll be another unseasonably warm day, and utilizing the low level thickness forecast with the MOS consensus and NBM, we arrive at highs in the mid and upper 80s away from the immediate coast. Tonight: Ridging aloft builds overhead, while a weak pressure pattern is found at the surface that shows Bermuda high pressure offshore, another high near the Appalachians and a broad, but weak trough in the local vicinity. The loss of heating will quickly allow for convection along the sea breeze to come to an end, and the rest of the night will be rainfree. The biggest concern will be in regards to fog. Light to calm winds, subsidence with a fairly strong inversion trapping moisture underneath, and favorable condensation pressure deficits will produce at least patchy coverage to the fog. However, some guidance is hitting it harder, and shows not only greater coverage, but also some potential for dense fog. There`s a little cooler air that moves in as skies clear, allowing for lows to get a few degrees cooler than it was this morning. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Deep layered ridging will prevail Thursday into Friday. Despite a robust afternoon sea breeze both days and decent moisture advection, strong mid-level subsidence should maintain dry conditions. Above normal temperatures expected with highs in the mid to upper 80s. The upper ridge axis will shift just off the coast Saturday morning, allowing upper shortwave energy to move into the area from the west. Prevailing onshore flow should allow a sea breeze to develop fairly early in the day and progress inland. The best convergence and forcing for convection will exist inland. Greater sky cover will knock a few degrees off high temps, with low/mid 80s expected. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... A quasi-zonal flow will exist Saturday night through Monday, with a series of upper shortwaves moving through. Fairly deep moisture will be in place, and a good sea breeze will develop each day. Isolated to scattered showers and thunderstorms expected during the period. Broad upper ridging Monday night through Tuesday will bring mainly dry conditions with temperatures climbing into the 90s in many areas. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... KCHS/KJZI/KSAV: Lingering showers near KCHS and KJZI early this morning associated with a short wave will come to an end. Meanwhile, some low stratus and light fog will impact KSAV early in the forecast cycle. The next chance for convection will be this afternoon and evening, as isolated to scattered SHRA/TSRA forms along the sea breeze. We will include VCTS at all terminals between 18Z and 23Z, with the potential for brief MVFR conditions should a direct impact occur. Late tonight there will be the formation of some low stratus and fog. Sub-VFR conditions are likely. Extended Aviation Outlook: Flight restrictions possible in overnight/early morning fog and stratus. Scattered showers and thunderstorms Saturday through Sunday. && .MARINE... Today and tonight: The local waters will lie under or near the western periphery of Bermuda high pressure, while a subtle trough is found over nearby land areas. The resulting pressure pattern is relaxed, and even with sea breeze circulations this afternoon and evening, wind speeds will mainly be no higher than 10 or perhaps 15 kt. Seas will be just 2 or 3 feet. Late tonight there will be the formation of some fog over land areas, some of which could move into the Charleston Harbor and the Atlantic waters very close to shore. No marine concerns expected Thursday through Monday. Atlantic high pressure will remain the dominant feature with a relatively weak gradient in the area. Wind speeds will generally stay below 10 kt except right along the coast with the afternoon sea breeze, and seas will mostly run 2-3 ft. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM...JRL LONG TERM...JRL AVIATION... MARINE...