744 FXUS62 KCHS 301051 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 651 AM EDT Tue Aug 30 2022 .SYNOPSIS... A trough of low pressure near the coast will move offshore later today, then a cold front will move through Wednesday. A series of disturbances will affect the area Friday through early next week. && .NEAR TERM /THROUGH TONIGHT/... A quick update has been issued to issue a Dense Fog Advisory from Allendale County to Long County. DOT webcams and surface observations show the dense fog has become widespread enough to justify a Dense Fog Advisory for the morning commute. The advisory goes through 9 AM. A weak low appears to have formed in the inverted trough this morning and was centered near Beaufort at 30/09z. The risk for measurable rainfall will be highest along/east of Highway 17 in Charleston County over the next few hours as this wave moves up the coast. There is a chance that the low will enhance convection along the middle South Carolina coast so there remains a risk for flooding across mainly Charleston County, including Downtown Charleston, through about 9 AM. Near term pops were adjusted slightly per KCLX reflectivity trends. Locally dense fog continues across far interior Southeast Georgia. Early morning water vapor imagery shows a persistent mid-level weakness and associated shear axis over the Southeast U.S. Coast along the western periphery of the large subtropical ridge centered well offshore. An inverted trough was noted along the Georgia and far southern South Carolina coasts. Numerous to widespread showers/tstms were in place from north coastal Georgia to just south of the Charleston Metro Area. The main forecast challenges center on how quickly ongoing morning convection and its near term heavy rain/minor flood threat will exit the coast later this morning with another round of showers/tstms possible this afternoon and evening. Today through This Evening: The bulk of the early morning convection will shift offshore by daybreak as the shear axis and associated vorticity center exit off the coast leaving much of the morning rain-free with the exception of a few lingering coastal showers. Later this afternoon, building mixed- layer instability coupled with a very moisture rich airmass will support yet another round of convection this afternoon and evening. Model theta-e progs and modified soundings show the deepest moisture and instability will be aligned along the Georgia coast and extending farther west roughly along/south south of the I-16 corridor. Farther north, moisture will still be plentiful, but lingering low-level cloud cover from morning convection will likely dampen temperatures rises through day yielding less net mixed-layer instability. Pops will range from 50-60% across coastal Georgia to 30-40% elsewhere elsewhere across Southeast South Carolina and Southeast Georgia. A risk for locally heavy rainfall/minor flooding will continue, mainly along coastal Georgia including the Savannah Metro Area where a quick 1-3" of rain could fall in a very short period of time. Highs will range from the lower-mid 80s across the Charleston Tri-County area to the upper 80s/near 90 elsewhere away from the beaches. Overnight: A strong shortwave digging southeast out of the Ohio Valley will reinforce the mid-level weakness across the Southeast U.S. tonight. Low-level winds over the Atlantic will respond which will increase convergence across the waters after midnight. Isolated to scattered showers/tstms are likely to develop in response to this with the mean steering flow pattern favoring keeping the bulk of this activity offshore. However, some of this may brush the coast, especially the middle South Carolina coast prior to daybreak. Pops will range 20-30% at the coast with pops below mentionable thresholds across the far interior. Some patches of fog and stratus could develop west of I-95 some of which could become locally dense. Lows will range from the lower 70s well inland to the upper 70s at the beaches and Downtown Charleston. && .SHORT TERM /WEDNESDAY THROUGH FRIDAY/... A broad upper ridge will expand over the eastern United States Wednesday into Thursday while a cold front pushes south into the area. A drier airmass will try to push in from the northwest late Wednesday, though low-level flow will quickly become onshore by Thursday morning, bringing moisture back into coastal areas. The expansion of the upper ridge will produce large scale subsidence, limiting the potential for convection. However, with the cold front nearby and a weak sea breeze each afternoon, we cannot rule out at least isolated convection through the period. A coastal trough could move inland on Friday, along with a plume of deep tropical moisture, likely yielding scattered to numerous showers and tstms, especially during the afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... A series of upper disturbances will move through during the weekend and early next week, maintaining above normal rain chances. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... KCHS/KJZI: Showers/tstms should be exiting both KCHS and KJZI right around 12z. A decision to include any mention of SHRA/TSRA for this morning will made right before issuance time. Otherwise, MVFR cigs will prevail this morning. VFR will return by early afternoon. Scattered showers/tstms are expected to develop this afternoon, but confidence is not high for impacts to justify a mention at either terminal at this time. Isolated showers could be near the terminals late tonight (especially KJZI), but most of this activity looks to remain over the Atlantic. KSAV: Satellite and surface observations show the leading edge of LIFR cigs is holding just west of the terminal. There is still a chance these cigs (below alternate minimums) will impact the terminal through 13z so a TEMPO will likely be needed to address this. Otherwise, MVFR cigs will prevail through late morning, then improving to VFR this afternoon. Scattered to numerous showers/tstms are expected over coastal Georgia this afternoon. A TEMPO for 4SM TSRA will be included 19-22z to account for any possible impacts. Extended Aviation Outlook: Although a shower or tstm could briefly restrict ceilings/vsbys at the terminals at any point, the best chance will be Friday through Saturday. && .MARINE... Through Tonight: There are no concerns. Southerly winds will prevail today, then veer to the southwest tonight. Speeds will be 15 kt or less with seas 2-4 ft. Wednesday through Sunday: A front will stall across the waters Wednesday into Thursday, then shift farther south on Friday. Winds will remain fairly weak until Friday when a northeast gradient develops. Even then, wind speeds will typically be no higher than 10-15 kt. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Dense Fog Advisory until 9 AM EDT this morning for GAZ087-088- 099-100-114-115-137. SC...Dense Fog Advisory until 9 AM EDT this morning for SCZ040. MARINE...None. && $$