FXUS62 KCHS 310347 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1047 PM EST Mon Jan 30 2023 .SYNOPSIS... A series of weak fronts will impact the region through mid-week. A stronger storm system will affect the area Thursday into Friday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Update: Seeing enough observation sites reporting visibilities of 3/4 of a mile or less and the trend certainly favors that to continue falling to 1/4 of a mile. Have gone with a Dense Fog Advisory for almost the entire forecast area. The only counties not included are Long, McIntosh, Liberty, Bryan, and Chatham. However, it is expected that the fog and low stratus will expand into these areas later on and the Dense Fog Advisory will likely need to be updated. Late this evening: Shower activity continues to dissipate and shift offshore along the Georgia coast. So far, only a few observation sites are reporting surface visibilities of a mile or less. Over the next several hours we still expect fog to increase in coverage and the potential for dense fog is certainly on the higher end. No change to the forecast at this point, still waiting for enough signs of fog to support Dense Fog Advisories. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... Tuesday: Morning low clouds/fog will linger through mid- morning. Zonal flow will remain in place aloft as subtropical ridging holds firm over Cuba. A weak cold front will stall over the area Tuesday. A few showers could develop in the vicinity of the boundary as weak warm air advection/isentropic ascent along the 295-305K surfaces persists. Major rainfall is unlikely with only a few hundredths likely to fall where showers occur. Pops 20-30% look reasonable for most areas. Warm/moist conditions will hold with highs warming into the upper 60s to mid 70s, warmest south of the I-16 corridor in Southeast Georgia. The stationary front will washout overnight, but increasing flow in the 1000-925 hPa layer ahead of yet another front will likely help to enhance isentropic forcing as weak warm air advection. Guidance shows a solid uptick in rain chances overnight and pops have been increased to 30-40% to reflect this. Another round of low clouds and possibly some fog due to stratus build-down could occur, but widespread dense fog is not currently expected due to increasing boundary layer winds. Patchy fog will be introduced to trend. It will be a somewhat warm and humid night with the area fully embedded in the pre-frontal warm sector. Lows will only drop into the mid-upper 50s which is about 15-20 degrees above normal. Wednesday: A cold front will drop south through the area Wednesday as high pressure begins to wedge down from the north. Guidance is fairly consistent in keeping the main corridor of channeled vorticity displaced well to the north coincident with the 500 hPa jet, so rain chances will remain somewhat limited with the lack of any meaningful deep layered UVVs. Weak isentropic forcing atop the developing wedge will keep a risk for isolated to perhaps scattered showers in place, but significant rainfall is unlikely. Highs Wednesday afternoon will be closely tied to how quickly the wedge can expand south. Highs look to warm into the lower-mid 60s north of the I-26 corridor to the upper 60s/lower 70s elsewhere, but confidence in this is only moderate at best given the wedge front could drive south quicker than expected. Overnight, the wedge will begin to steadily erode as the wedge front begins to lift north as a warm front. This is in response to cyclogenesis occurring along an approaching cold front as a potent shortwave digs across the Southern Plains. There will be a risk for isolated to scattered showers impacting the area as the warm front lifts north. Lows will range from the upper 40s/lower 50s across northern areas to the mid-upper 50s across the south. If the warm front sharpens more than expected, temperatures could rise late. Thursday: The southern stream shortwave moving across the Southern Plains will gradually phase with secondary shortwave energy propagating over the Great Lakes Thursday night. Strong forcing ahead of this mean trough coupled with a high theta-e airmass in place across much of Southeast U.S. will likely support a large swath of moderate to locally heavy rains extending from the Deep South into the Virginia Tidewater. Most of this activity will likely remain west of the local area through the day, only approaching the far western zones closer to sunset. However, a few showers could still occur in the vicinity of the retreating wedge/warm front across northern areas through the day. Highs will range from the upper 50s/lower 60s near the Santee River (near the retreating wedge/warm front) to mid-upper 60s over southern South Carolina with lower- mid 70s across Southeast Georgia. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A well-defined frontal band of moderate to locally heavy rain will push through the area Thursday night into Friday as a cold front works its way offshore Friday morning. Pre-frontal instability looks minimal and with the front taking on more of an anafrontal structure, it appears the chances for tstms is minimal given most of the rain will occur along/behind the frontal surface. Given the anafront structure, it may take much of the daytime hours Friday for the rain to finally clear the coast. Freezing temperatures are expected across the far interior Friday night, but any lingering showers should be offshore prior to the arrival of any risk for p- type issues. A coastal trough could bring another round of showers Saturday night into Sunday before another cold front clears the coast Monday. Temperatures will return to more seasonal levels for much of the extended period. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... The 00z TAF period begins with at least MVFR conditions everywhere across the forecast area, and much of the area is under IFR conditions. It might take a couple of hours for IFR ceilings to really settle in at the terminals, but once they do they will remain through the rest of the overnight and likely most of the morning. In fact, conditions appear quite supportive of stratus building down and helping to produce dense fog later tonight. The TAF's feature 1/2SM visibilities in fog beginning around 05-07z and continuing through mid morning. An improvement to MVFR isn't likely until midday, and it is possible conditions will remain sub-VFR through the end of the forecast period. Isolated showers will be possible as early as mid morning Tuesday, but the chances of direct impacts are too low to include explicitly in the forecast at this point. Extended Aviation Outlook: Widespread stratus with some vsby restrictions is likely Monday night/Tuesday morning. Rain is likely Thursday into Friday as a cold front pushes through the region. && .MARINE... Late evening update: Web cams around Charleston Harbor indicate that dense fog has moved in and there is no reason to think it will not stick around the rest of the night. Therefore, we have issued a Dense Fog Advisory for Charleston Harbor and the South Carolina waters. Dense fog might not be ongoing across the nearshore waters, but will very likely begin soon. The Dense Fog Advisory will likely need to be expanded to include the Georgia waters in the next few hours. Tonight: A stationary front will meander along the coastal waters. A minimal pressure gradient will cause winds to be very light and variable tonight. Likewise, seas will be 2-3 ft. The main concern is stratus building down to form sea fog this evening and overnight. Given the aforementioned winds and an inversion, areas of dense fog should be easy to form across the waters, including the Charleston Harbor as well. Marine Dense Fog Advisories may eventually be needed. Tuesday through Saturday: A series of weak fronts will affect the waters through mid-week, but no major impacts are expected. A strong cold front will push into the waters Thursday night into Friday. Northeast winds will prevail Friday night into Saturday. There is a chance both winds and seas could reach Small Craft Advisory levels Thursday night through Saturday, but confidence remains fairly low at this time. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Dense Fog Advisory until 10 AM EST Tuesday for GAZ087-088- 099>101-114-115. SC...Dense Fog Advisory until 10 AM EST Tuesday for SCZ040-042>045- 047>052. MARINE...Dense Fog Advisory until 10 AM EST Tuesday for AMZ330-350-352. && $$ NEAR TERM...BSH SHORT TERM... LONG TERM... AVIATION...BSH MARINE...