Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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692 FXUS62 KCHS 011433 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1033 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/... Morning satellite and upper air charts reveal a well defined short-wave spinning off the North Carolina coast into the Atlantic and slightly lower heights/cooler air aloft across the coastal Carolinas into southeast Georgia. Early morning showers along the southern periphery of the wave have weakened and moved into the Atlantic. Morning fog/stratus is eroding/mixing out. Rest of today: Upper level troughiness will weaken as upstream ridging builds into the southeast coast through the afternoon, although modestly cooler mid level air will linger into tonight. With those cooler mid level temps, high resolution forecast guidance and soundings show the development of 500-1000 J/Kg MLCAPE this afternoon across the South Carolina counties...a bit lower through southeast Georgia where mid level temps will be warmer. Minimal larger scale forcing for ascent will exist across the region this afternoon. But prevailing westerly low level flow and development of the sea breeze will lead to respectable convergence along the coast this afternoon with RAP13 guidance suggesting the strongest convergence will be across the South Carolina counties. Upshot: Some pop-up showers and thunderstorms are a good bet along the inland pressing sea breeze after 2 pm with the higher probabilities looking to be across the South Carolina counties. Severe storm risk is low, although SPC RAP data does show just a touch (25-30 knots) of effective bulk shear across the SC coastal areas...owing to modestly stronger mid level northwesterly flow. This might support a stronger updraft or two. 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 /14Z 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 KCHS and KSAV between about 19Z and 23Z, with the potential for brief MVFR conditions should a direct impact occur. For the moment the sea breeze looks to be inland from KJZI before activity develops along it. 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...Adam SHORT TERM...JRL LONG TERM...JRL