|
Show Area Forecast Discussion - Charleston, SC (Charleston, SC Area) Selection: |
| #1232567 (Received by flhurricane at: 3:54 AM 30.May.2025) AFDCHS Area Forecast Discussion National Weather Service Charleston SC 348 AM EDT Fri May 30 2025 .SYNOPSIS... A cold front will sweep through our area this evening. High pressure will build in over the weekend and prevail through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... A shortwave will move east of the area by daybreak. Lingering debris cloudiness should burn off by mid-morning as NVA develops in its wake. Veering BL wind profiles will produce some compressional heating which, along with mostly sunny skies late morning into early afternoon, should push temps into the mid to upper 80s. With the mixed layer expanding to about 5 kft, surface dewpoints may mix out somewhat, though blended guidance still keeps values in the upper 60s in most areas. PWs will see a late morning minimum before increasing back above 1.75" later this afternoon. A shortwave will move through central and eastern NC later this afternoon with a weaker vort moving through SC/GA. A cold front is expected to drop southeast into our forecast area late this afternoon and move offshore by midnight. The main question is coverage and intensity of convection ahead of the cold front. The veering BL flow will result in winds relatively parallel to the front by the time it reaches our area. This decrease in low-level convergence may result in a thinning or weakening convective band as it moves through. However, if a particularly robust MCS develops upstream it could hold its momentum as it moves into our area. Convective indices are forecast to be fairly impressive. 0-6 km bulk shear approaches 50 kt along the SC/GA coast late this afternoon while SBCAPE could be pushing 2000 J/kg in spots. Damaging winds would be the primary threat, though Lifted Indices of -6C would support some hail risk, and 1-2 EHI wouldn`t completely rule out an isolated tornado. It appears the earliest we could see the storms moving into our northwestern zones would be 2-3pm with the greatest threat window 4-8pm. Cooler, drier air will spread in from the west late this evening and overnight. Saturday morning lows could dip into the upper 50s away from the coast. && .SHORT TERM /SATURDAY THROUGH MONDAY/... The mid-levels will consist of a longwave trough over the East Coast Saturday morning, with an embedded Low north of New England. These features should hover in place through Sunday. By Sunday night, the Low lifts further north and weakens, while a weak shortwave rounds the base of the trough, moving over our area late Sunday night or Monday morning. The trough axis should then shift offshore late Monday, followed by ridging building in from the west. At the surface, High pressure centered over the Southern Plains Saturday morning will shift over the Lower MS Valley Saturday evening, then near the FL Panhandle Sunday morning, while weakening and becoming diffuse. The weak High may be in the vicinity of our area Sunday evening. Additionally, a dissipating cold front may move through our area late Sunday night. Afterwards, High pressure is expected to strengthen over the Middle Appalachians Monday morning, then passing to our north by later Monday. The High is expected to be the primary synoptic feature in our area, limiting moisture. PWATs should drop below 1" on Saturday before rising back above 1" Saturday evening/night, then continuing to rise to ~1.25" by late Sunday. All of these values are below normal. Hence, the deterministic models keep our area dry on Saturday. Some models hint at upstream convection making it to our area late in the day Sunday and Monday. But given the PWATs, it might be hard to get any rainfall. So we kept the forecast dry. High temperatures will peak in the low to mid 80s Saturday, then rise to the mid to upper 80s Sunday and Monday, except cooler at the beaches due to the sea breeze. Saturday and Sunday night lows should range from the lower 60s far inland to the upper 60s/lower 70s at or near the beaches. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... Mid-level ridging will build over the East Coast Monday night into Tuesday, then possibly prevail through Thursday. Surface High pressure initially over the Middle Appalachians should shift into the Atlantic, all while being the dominant weather feature for our weather. This will lead to mostly dry conditions and gradually rising temperatures each day. && .AVIATION /07Z FRIDAY THROUGH TUESDAY/... MVFR or lower ceilings expected to develop at all terminals a few hours prior to daybreak today, then persist into mid to late morning before clearing out. A band of thunderstorms may precede a cold front late this afternoon or early this evening. The activity may be on a diminishing trend by the time it reaches the terminals so we only included VCTS in the 06Z TAFs. If we do see convection at the terminals, vsby and/or ceiling reductions would be quite short-lived. Extended Aviation Outlook: Gusty W winds are possible on Saturday. Otherwise, VFR should prevail. && .MARINE... SW to WSW winds will increase late this morning through the afternoon as a cold front approaches. Wind gusts in Charleston Harbor and the nearshore Charleston County waters could reach 25 kt for a few hours late this afternoon through early evening. For now we capped winds at 15-20 kt in both zones given the marginal nature and low-confidence, however later shifts may need to reassess for a possible Small Craft Advisory. Winds become W or NW later tonight. There should be a surge in SW winds later Saturday. But wind gusts should stay below 25 kt, so no Small Craft Advisories are expected. Conditions improve more on Sunday, with no major concerns later into the week. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ |
